Filarial infection suppresses malaria-specific multifunctional Th1 and Th17 responses in malaria and filarial coinfections

Subclinical Inflammation in Asymptomatic Schoolchildren With Plasmodium falciparum Parasitemia Correlates With Impaired Cognition

BACKGROUND

Subclinical inflammation and cognitive deficits have been separately associated with asymptomatic Plasmodium falciparum infections in schoolchildren. However, whether parasite-induced inflammation is associated with worse cognition has not been addressed. We conducted a cross-sectional pilot study to better assess the effect of asymptomatic P. falciparum parasitemia and inflammation on cognition in Kenyan schoolchildren.

METHODS

We enrolled 240 children aged 7-14 years residing in high malaria transmission in Western Kenya. Children performed five fluid cognition tests from a culturally adapted NIH toolbox and provided blood samples for blood smears and laboratory testing. Parasite densities and plasma concentrations of 14 cytokines were determined by quantitative PCR and multiplex immunoassay, respectively. Linear regression models were used to determine the effects of parasitemia and plasma cytokine concentrations on each of the cognitive scores as well as a composite cognitive score while controlling for age, gender, maternal education, and an interaction between age and P. falciparum infection status.

RESULTS

Plasma concentrations of TNF, IL-6, IL-8, and IL-10 negatively correlated with the composite score and at least one of the individual cognitive tests. Parasite density in parasitemic children negatively correlated with the composite score and measures of cognitive flexibility and attention. In the adjusted model, parasite density and TNF, but not P. falciparum infection status, independently predicted lower cognitive composite scores. By mediation analysis, TNF significantly mediated ~29% of the negative effect of parasitemia on cognition.

CONCLUSIONS

Among schoolchildren with PCR-confirmed asymptomatic P. falciparum infections, the negative effect of parasitemia on cognition could be mediated, in part, by subclinical inflammation. Additional studies are needed to validate our findings in settings of lower malaria transmission and address potential confounders that could affect both inflammation and cognitive performance.

CD4+ Th1 and Th17 responses and multifunctional CD8 T lymphocytes associated with cure or disease worsening in human visceral leishmaniasis

Introduction

In VL, a proinflammatory phenotype is typically associated with enhanced phagocytosis and a Th1 mediated immune response resulting in infection control. In contrast, an anti-inflammatory phenotype, associated with a predominant regulatory response, typically enables intracellular multiplication of Leishmania parasites and disease progression.

Methods

To investigate the impact of chemotherapy on Th2 and Th17 immune responses in patients with visceral leishmaniasis (VL), we assessed all combinations of intracellular expression of IFN-γ, IL-10, IL-4 and IL-17 in the CD4+ and CD8+ T cell populations of peripheral blood mononuclear cell (PBMC) samples from patients, after antigenic stimulation with Leishmania lysate, throughout treatment and follow-up. As increases in spleen and liver sizes and decreases in hematocrit, hemogloblin, erythrocytes, monocytes, leukocytes and platelets levels are strongly related to the disease, we studied the correlations between the frequencies of T cells producing the afore mentioned cytokines, individually and in combination, and these variables, as markers of disease or cure.

Results

We found that the frequency of IFN-γ-producingCD4+ T cells increased until the end of chemotherapy with Glucantime® or AmBisome ®, while IL-10, IL-4 and IL-17-producing CD4+ T cells peaked on day 7 following the start of treatment. Although the frequency of CD4+IL-17+ cells decreased during treatment an increase was observed after clinical cure. The frequency of CD4+ T cells producing only IFN-γ or IL-17 correlated with blood monocytes levels. Frequencies of double-producers of IFN-γ and IL-10 or IL-4 correlated positively with eosinophils and platelets levels. Together, this suggest that IFN-γ drives the immune response towards Th1 at cure. In contrast, and associated with disease or Th2 response, the frequency of CD4+ IL-10+ cells correlated positively with spleen sizes and negatively with circulating monocyte levels, while the frequency of CD4+ producing both IL-4 and IL-10 correlated negatively with platelets levels. The frequency of CD8+ single-producers of IFN-γ increased from day 21 to 90 while that of single-producers of IL-10 peaked on day 7, of IL-4 on day 30 and of IL-17, on day 180. IFN-γ expression in CD8+ single- and double-producers of cytokines was indicative of an immune response associated with cure. In contrast, frequencies of CD8+ double-producers of IL-4 and IL-10, IL-4 and IL-17 and IL-10 and IL-17 and producers of three and four cytokines, were associated with disease and were low after the cure. Frequencies of CD8+ T cells producing IFN-γ alone or with IL-17 were positively correlated with platelets levels. In contrast, as markers of disease: 1) frequencies of single producers of IL-10 correlated negatively with leukocytes levels, 2) frequencies of double producers of IL-4 and IL-10 correlated negatively with platelet, leukocyte, lymphocyte and circulating monocyte levels, 3) frequencies of triple-producers of IFN-γ, IL-4 and IL-10 correlated negatively with platelet, leukocyte and neutrophil levels and 4) frequencies of producers of IFN-γ, IL-4, IL-10 and IL-17 simultaneously correlated positively with spleen size, and negatively with leukocyte and neutrophil levels.

Discussion

Our results confirmed that the clinical improvement of VL patients correlates with the decrease of an IL-4 and IL-10 CD4+Th2 response, the recovery of CD4+ Th1 and Th17 responses and the frequency of CD8+ single-producers of IFN-γ and double producers of IFN-γ and IL-17.

Prevalence, probability, and characteristics of malaria and filariasis co-infections: A systematic review and meta-analysis

BACKGROUND

Malaria and filariasis are significant vector-borne diseases that are co-endemic in the same human populations. This study aims to collate the evidence, probability, and characteristics of malaria and filariasis co-infections in participants among studies reporting the co-occurrence of both diseases.

METHODS

We searched for potentially relevant articles reporting the co-occurrence of malaria and filariasis in five electronic databases (Embase, PubMed, Scopus, Medline, and CENTRAL) from inception to May 22, 2022. We estimated the pooled prevalence and probability of malaria and filariasis co-infections among study participants using random-effects meta-analyses and synthesized the characteristics of patients with co-infections narratively.

RESULTS

We identified 951 articles, 24 of which (96,838 participants) met eligibility criteria and were included in the systematic review. Results of the meta-analysis showed a pooled prevalence of malaria and filariasis co-infections among participants of 11%. The prevalence of co-infections was 2.3% in Africa, 0.2% in Asia, and 1.6% in South America. The pooled prevalences of malaria and Wuchereria bancrofti, malaria and Loa loa, malaria and Mansonella perstans co-infections were 0.7%, 1.2%, and 1.0%, respectively. The meta-analysis results showed that the co-infections between two parasites occurred by probability (P = 0.001). Patients with co-infections were at increased risk of having an enlarged spleen, a lower rate of severe anemia, lower parasite density, and more asymptomatic clinical status. Patients with co-infections had decreased levels of C-X-C motif chemokine 5, tumor necrosis factor-α, interleukin-4, c4 complement, and interleukin-10. In addition, patients with co-infections had a lower interleukin-10/tumor necrosis factor-α ratio and higher interleukin-10/interleukin-6 ratio.

CONCLUSION

The present study showed that the prevalence of malaria and filariasis co-infections was low and varied between geographical areas in the selected articles. Co-infections tended to occur with a low probability. Further studies investigating the outcomes and characteristics of co-infections are needed.

A filarial parasite-encoded human IL-10 receptor antagonist reveals a novel strategy to modulate host responses

Interleukin (IL)-10 is the primary cytokine driving the modulation of the host response in filarial infections. We performed binding assays with Brugia malayi antigen extracts and human IL-10R1. Bm5539 was the top-binding hit. We identified a short sequence, termed truncated Bm5339, that has structural similarities to the human IL-10 functional dimer. Sequence comparisons revealed that other filarial parasites possess Bm5539 orthologues. Using recombinant Bm5539 in a modified Luciferase Immunoprecipitation System assay, we confirmed that both the truncated and full-length forms of the protein can bind to human IL-10R1. Truncated Bm5539 could inhibit human IL-10-driven phosphorylation of STAT3, thereby demonstrating that Bm5539 acts as an IL-10 antagonist, most likely through competitive binding to the receptor. We provide a structural basis for these observations using computational modeling and simulations. This parasite-encoded cytokine receptor antagonist provides an additional lens through which parasite-induced modulation of the host immune response can be examined.

Spleen nodules in Loa loa infection: re-emerging knowledge and future perspectives

Loiasis, the infection with the vector-borne filarial nematode Loa loa, is widely distributed in central and west Africa. Long considered a rather benign infection, recently loiasis with high microfilarial burden was associated with increased mortality risk. Eyeworm and Calabar swelling are pathognomonic signs of the infection, but other atypical, non-specific manifestations can also occur. For instance, splenic nodules have been seldom reported. In this Grand Round, we report two cases of loiasis in migrants who presented with spleen nodules, which could be followed up over time (up to 27 months) with multiple imaging techniques until their resolution. We comment on the clinical implications of these observations, including differential diagnosis with similar imaging findings, and critically review the evidence of spleen involvement in loiasis and other filarial infections.

Whole blood transcriptome analysis in onchocerciasis

Identifying the molecular mechanisms controlling the host’s response to infection with Onchocerca volvulus is important to understand how the human host controls such parasitic infection. Little is known of the cellular immune response upon infection with O. volvulus. We performed a transcriptomic study using PAXgene-preserved whole blood from 30 nodule-positive individuals and 21 non-endemic controls. It was found that of the 45,042 transcripts that were mapped to the human genome, 544 were found to be upregulated and 447 to be downregulated in nodule-positive individuals (adjusted P-value < 0.05). Pathway analysis was performed on this set of differentially expressed genes, which demonstrated an impact on oxidative phosphorylation and protein translation. Upstream regulator analysis showed that the mTOR associated protein RICTOR appears to play an important role in inducing the transcriptional changes in infected individuals. Functional analysis of the genes affected by infection indicated a suppression of antibody response, Th17 immune response and proliferation of activated T lymphocytes. Multiple regression models were used to select 22 genes that could contribute significantly in the generation of a classifier to predict infection with O. volvulus. For these 22 genes, as well as for 8 reference target genes, validated RT-qPCR assays were developed and used to re-analyze the discovery sample set. These data were used to perform elastic net regularized logistic regression and a panel of 7 genes was found to be the best performing classifier. The resulting algorithm returns a value between 0 and 1, reflecting the predicted probability of being infected. A validation panel of 69 nodule-positive individuals and 5 non-endemic controls was used to validate the performance of this classifier. Based on this validation set only, a sensitivity of 94.2% and a specificity of 60.0% was obtained. When combining the discovery test set and validation set, a sensitivity of 96.0% and a specificity of 92.3% was obtained. Large-scale validation approaches will be necessary to define the intended use for this classifier. Besides the use as marker for infection in MDA efficacy surveys and epidemiological transmission studies, this classifier might also hold potential as pharmacodynamic marker in macrofilaricide clinical trials.

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Whole blood transcriptome analysis was performed in onchocerciasis patients.

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Suppression of antibodies, Th17, and proliferation of activated T cells.

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RICTOR plays an important role in inducing the transcriptional changes.

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A 7-gene expression classifier was built as a tool for onchocerciasis detection.

Inflammatory cytokine responses in children with asymptomatic malaria infection living in rural, semi-urban and urban areas in south-eastern Gabon

Cytokines are soluble mediators of the immune response, and their evolution influences the disease outcome. Gaining knowledge on cytokines has become important, as they can constitute biomarkers allowing the diagnosis of malaria and preventing severe forms of the disease. Here, we investigated 10 cytokines and their circulating levels in asymptomatic Gabonese children with Plasmodium falciparum infection living in urban, semi-urban and rural areas. Blood samples were collected from 273 schoolchildren (153 uninfected and 120 infected) aged 6 to 192 months. Hematological parameters were determined and P. falciparum diagnosis was performed using a rapid diagnosis test, microscopy and nested polymerase chain reaction (PCR). Plasma pro- [interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-12p70, IL-17A and IL-22] and anti-inflammatory [IL-10, IL-4, IL-13 and transforming growth factor (TGF)-β] cytokine levels were measured by enzyme-linked immunosorbent assay (ELISA) and compared between asymptomatic-infected and uninfected children. Results revealed that without distinction of area, IL-10 and IL-6 levels were higher in infected compared to uninfected children; however, the pro- and anti-inflammatory ratios (IL-6/IL-10 and TNF-α/IL-10) were similar. Furthermore, with area distinction significantly elevated levels of IL-10 in these asymptomatic children were always accompanied by either significantly low or high levels of a proinflammatory cytokine. Also, comparison between asymptomatic-infected children from the three areas showed significantly lower IL-17A, IL-22 and TGF-β levels in urban area compared to semi-urban and rural areas. These results suggest that asymptomatic malaria infections induce significantly high inflammatory cytokine levels without modifying the balanced between pro- and anti-inflammatory cytokines and underline the higher exposure to infections of children in rural areas.

IL-10 and Its Related Superfamily Members IL-19 and IL-24 Provide Parallel/Redundant Immune-Modulation in Loa loa Infection

BACKGROUND

Interleukin-10 (IL-10) has been implicated as the major cytokine responsible for the modulation of parasite-specific responses in filarial infections; however, the role of other IL-10 superfamily members in filarial infection is less well studied.

METHODS

Peripheral blood mononuclear cells from loiasis patients were stimulated with or without filarial antigen. Cytokine production was quantified using a Luminex platform and T-cell expression patterns were assessed by flow cytometry.

RESULTS

All patients produced significant levels of IL-10, IL-13, IL-5, IL-4, and IL-9 in response to filarial antigen, indicating a common infection-driven response. When comparing microfilaria (mf)-positive and mf-negative patients, there were no significant differences in spontaneous cytokine nor in parasite-driven IL-10, IL-22, or IL-28a production. In marked contrast, mf-positive individuals had significantly increased filarial antigen-driven IL-24 and IL-19 compared to mf-negative subjects. mf-positive patients also demonstrated significantly higher frequencies of T cells producing IL-19 in comparison to mf-negative patients. T-cell expression of IL-19 and IL-24 was positively regulated by IL-10 and IL-1β. IL-24 production was also regulated by IL-37.

CONCLUSION

These data provide an important link between IL-10 and its related family members IL-19 and IL-24 in the modulation of the immune response in human filarial infections.

CLINICAL TRIALS REGISTRATION

NCT00001230.

Altered Ex-Vivo Cytokine Responses in Children With Asymptomatic Plasmodium falciparum Infection in Burkina Faso: An Additional Argument to Treat Asymptomatic Malaria?

Introduction

Patients with clinical malaria have an increased risk for bacterial bloodstream infections. We hypothesized that asymptomatic malaria parasitemia increases susceptibility for bacterial infections through an effect on the innate immune system. We measured circulating cytokine levels and ex-vivo cytokine production capacity in asymptomatic malaria and compared with controls.

Methods

Data were collected from asymptomatic participants <5 years old with and without positive malaria microscopy, as well as from hospitalized patients <5 years old with clinical malaria, bacteremia, or malaria/bacteremia co-infections in a malaria endemic region of Burkina Faso. Circulating cytokines (TNF-α, IFN-γ, IL-6, IL-10) were measured using multiplex assays. Whole blood from asymptomatic participants with and without positive malaria microscopy were ex-vivo stimulated with S. aureus, E. coli LPS and Salmonella Typhimurium; cytokine concentrations (TNF-α, IFN-γ, IL-1β, IL-6, IL-10) were measured on supernatants using ELISA.

Results

Included were children with clinical malaria (n=118), bacteremia (n=22), malaria and bacteremia co-infection (n=9), asymptomatic malaria (n=125), and asymptomatic controls (n=237). Children with either clinical or asymptomatic malaria had higher plasma cytokine concentrations than controls. Cytokine concentrations correlated positively with malaria parasite density with the strongest correlation for IL-10 in both asymptomatic (r=0.63) and clinical malaria (r=0.53). Patients with bacteremia had lower circulating IL-10, TNF-α and IFN-γ and higher IL-6 concentrations, compared to clinical malaria. Ex-vivo whole blood cytokine production to LPS and S. aureus was significantly lower in asymptomatic malaria compared to controls. Whole blood IFN-γ and IL-10 production in response to Salmonella was also lower in asymptomatic malaria.

Interpretation

In children with asymptomatic malaria, cytokine responses upon ex-vivo bacterial stimulation are downregulated. Further studies are needed to explore if the suggested impaired innate immune response to bacterial pathogens also translates into impaired control of pathogens such as Salmonella spp.

Extracellular vesicles released from the filarial parasite Brugia malayi downregulate the host mTOR pathway

We have previously shown that the microfilarial (mf) stage of Brugia malayi can inhibit the mammalian target of rapamycin (mTOR; a conserved serine/threonine kinase critical for immune regulation and cellular growth) in human dendritic cells (DC) and we have proposed that this mTOR inhibition is associated with the DC dysfunction seen in filarial infections. Extracellular vesicles (EVs) contain many proteins and nucleic acids including microRNAs (miRNAs) that might affect a variety of intracellular pathways. Thus, EVs secreted from mf may elucidate the mechanism by which the parasite is able to modulate the host immune response during infection. EVs, purified from mf of Brugia malayi and confirmed by size through nanoparticle tracking analysis, were assessed by miRNA microarrays (accession number GSE157226) and shown to be enriched (>2-fold, p-value<0.05, FDR = 0.05) for miR100, miR71, miR34, and miR7. The microarray analysis compared mf-derived EVs and mf supernatant. After confirming their presence in EVs using qPCR for these miRNA targets, web-based target predictions (using MIRPathv3, TarBAse and MicroT-CD) predicted that miR100 targeted mTOR and its downstream regulatory protein 4E-BP1. Our previous data with live parasites demonstrated that mf downregulate the phosphorylation of mTOR and its downstream effectors. Additionally, our proteomic analysis of the mf-derived EVs revealed the presence of proteins commonly found in these vesicles (data are available via ProteomeXchange with identifier PXD021844). We confirmed internalization of mf-derived EVs by human DCs and monocytes using confocal microscopy and flow cytometry, and further demonstrated through flow cytometry, that mf-derived EVs downregulate the phosphorylation of mTOR in human monocytes (THP-1 cells) to the same degree that rapamycin (a known mTOR inhibitor) does. Our data collectively suggest that mf release EVs that interact with host cells, such as DC, to modulate host responses.

Lymphatic filariasis, a neglected tropical disease caused by parasitic worms which affects millions of individuals, represents an important public health concern due to its high morbidity that significantly diminishes quality of life. The parasite is able to establish a chronic infection by manipulating its host’s immune responses. The larval mf stage of the parasite is of particular interest as the parasites are present in the peripheral blood and in constant contact with the host’s immune cells. We decided to investigate the role of mf-derived EVs in the modulation of human antigen presenting cells during infection. We showed that mf release EVs that are similar to exosomes, and these parasite vesicles are readily internalized by human DC. The mf-derived EVs possess a unique miRNA profile and are enriched in miRNAs that can target the mTOR pathway. We have also demonstrated that purified mf-derived EVs are capable of inhibiting mTOR signaling in human monocytes. Collectively, our results suggest that mf release exosome-like vesicles that modulate the immune metabolism of host antigen presenting cells.

Beneficial effects of Strongyloides venezuelensis antigen extract in acute experimental toxoplasmosis

BACKGROUND

Toxoplasma gondii is a protozoan with worldwide distribution and triggers a strong Th1 immune response in infected susceptible hosts. On the contrary, most helminth infections are characterized by Th2 immune response and the use of helminth-derived antigens to regulate immune response in inflammatory disorders has been broadly investigated.

OBJECTIVES

The aim of this study was to investigate whether treatment with Strongyloides venezuelensis antigen extract (SvAg) would alter immune response against T gondii.

METHODS

C57BL/6 mice were orally infected with T gondii and treated with SvAg, and parasitological, histological and immunological parameters were investigated.

RESULTS

It was observed that SvAg treatment improved survival rates of T gondii-infected mice. At day 7 post-infection, the parasite load was lower in the lung and small intestine of infected SvAg-treated mice than untreated infected mice. Remarkably, SvAg-treated mice infected with T gondii presented reduced inflammatory lesions in the small intestine than infected untreated mice and decreased intestinal and systemic levels of IFN-γ, TNF-α and IL-6. In contrast, SvAg treatment increased T gondii-specific IgA serum levels in infected mice.

CONCLUSIONS

S venezuelensis antigen extract has anti-parasitic and anti-inflammatory properties during T gondii infection suggesting as a possible alternative to parasite and inflammation control.

Implications of asymptomatic infection for the natural history of selected parasitic tropical diseases

Progress has been made in the control or elimination of tropical diseases, with a significant reduction of incidence. However, there is a risk of re-emergence if the factors fueling transmission are not dealt with. Although it is essential to understand these underlying factors for each disease, asymptomatic carriers are a common element that may promote resurgence; their impact in terms of proportion in the population and role in transmission needs to be determined. In this paper, we review the current evidence on whether or not to treat asymptomatic carriers given the relevance of their role in the transmission of a specific disease, the efficacy and toxicity of existing drugs, the Public Health interest, and the benefit at an individual level, for example, in Chagas disease, to prevent irreversible organ damage. In the absence of other control tools such as vaccines, there is a need for safer drugs with good risk/benefit profiles in order to change the paradigm so that it addresses the complete infectious process beyond manifest disease to include treatment of non-symptomatic infected persons.

T cell-mediated immunity to malaria

Immunity to malaria has been linked to the availability and function of helper CD4⁺ T cells, cytotoxic CD8⁺ T cells and γδ T cells that can respond to both the asymptomatic liver stage and the symptomatic blood stage of Plasmodium sp. infection. These T cell responses are also thought to be modulated by regulatory T cells. However, the precise mechanisms governing the development and function of Plasmodium-specific T cells and their capacity to form tissue-resident and long-lived memory populations are less well understood. The field has arrived at a point where the push for vaccines that exploit T cell-mediated immunity to malaria has made it imperative to define and reconcile the mechanisms that regulate the development and functions of Plasmodium-specific T cells. Here, we review our current understanding of the mechanisms by which T cell subsets orchestrate host resistance to Plasmodium infection on the basis of observational and mechanistic studies in humans, non-human primates and rodent models. We also examine the potential of new experimental strategies and human infection systems to inform a new generation of approaches to harness T cell responses against malaria.

Understanding P. falciparum Asymptomatic Infections: A Proposition for a Transcriptomic Approach

Malaria is still a significant public health burden in the tropics. Infection with malaria causing parasites results in a wide range of clinical disease presentations, from severe to uncomplicated or mild, and in the poorly understood asymptomatic infections. The complexity of asymptomatic infections is due to the intricate interplay between factors derived from the human host, parasite, and environment. Asymptomatic infections often go undetected and provide a silent natural reservoir that sustains malaria transmission. This creates a major obstacle for malaria control and elimination efforts. Numerous studies have tried to characterize asymptomatic infections, unanimously revealing that host immunity is the underlying factor in the maintenance of these infections and in the risk of developing febrile malaria infections. An in-depth understanding of how host immunity and parasite factors interact to cause malaria disease tolerance is thus required. This review primarily focuses on understanding anti-inflammatory and pro-inflammatory responses to asymptomatic infections in malaria endemic areas, to present the view that it is potentially the shift in host immunity toward an anti-inflammatory profile that maintains asymptomatic infections after multiple exposures to malaria. Conversely, symptomatic infections are skewed toward a pro-inflammatory immune profile. Moreover, we propose that these infections can be better interrogated using next generation sequencing technologies, in particular RNA sequencing (RNA-seq), to investigate the immune system using the transcriptome sampled during a clearly defined asymptomatic infection.

Inflammatory and regulatory CCL and CXCL chemokine and cytokine cellular responses in patients with patent Mansonella perstans filariasis

Mansonella perstans (Mp) filariasis is present in large populations in sub-Saharan Africa, and to what extent patent Mp infection modulates the expression of immunity in patients, notably their cellular cytokine and chemokine response profile, remains not well known. We studied the spontaneous and inducible cellular production of chemokines (C-X-C motif) ligand 9 (CXCL9) [monokine induced by interferon (IFN)-γ (MIG)], CXCL-10 [inducible protein (IP)-10], chemokine (C-C motif) ligand 24 (CCL24) (eotaxin-2), CCL22 [macrophage-derived chemokine (MDC)], CCL13 [monocyte chemotactic protein-4 (MCP-4)], CCL18 [pulmonary and activation-regulated chemokine (PARC)], CCL17 [thymus- and activation-regulated chemokine (TARC)] and interleukin (IL)-27 in mansonelliasis patients (Mp-PAT) and mansonelliasis-free controls (CTRL). Freshly isolated peripheral mononuclear blood cells (PBMC) were stimulated with helminth, protozoan and bacterial antigens and mitogen [phytohaemagglutinin (PHA)]. PBMC from Mp-PAT produced spontaneously (without antigen stimulation) significantly higher levels of eotaxin-2, IL-27, IL-8, MCP-4 and MDC than cells from CTRL, while IFN-γ-IP-10 was lower in Mp-PAT. Helminth antigens activated IL-27 and MCP-4 only in CTRL, while Ascaris antigen, Onchocerca antigen, Schistosoma antigen, Entamoeba antigen, Streptococcus antigen, Mycobacteria antigen and PHA stimulated MIG release in CTRL and Mp-PAT. Notably, Entamoeba antigen and PHA strongly depressed (P < 0·0001) eotaxin-2 (CCL24) production in both study groups. Multiple regression analyses disclosed in Mp-PAT and CTRL dissimilar cellular chemokine and cytokine production levels being higher in Mp-PAT for CCL24, IL-27, IL-8, MCP-4, MDC and PARC (for all P < 0·0001), at baseline (P < 0·0001), in response to Entamoeba histolytica strain HM1 antigen (EhAg) (P < 0·0001), Onchocerca volvulus adult worm-derived antigen (OvAg) (P = 0·005), PHA (P < 0·0001) and purified protein derivative (PPD) (P < 0·0001) stimulation. In Mp-PAT with hookworm co-infection, the cellular chemokine production of CXCL10 (IP-10) was diminished. In summary, the chemokine and cytokine responses in Mp-PAT were in general not depressed, PBMC from Mp-PAT produced spontaneously and selectively inducible inflammatory and regulatory chemokines and cytokines at higher levels than CTRL and such diverse and distinctive reactivity supports that patent M. perstans infection will not polarize innate and adaptive cellular immune responsiveness in patients.

The Influence of Parasite Infections on Host Immunity to Co-infection With Other Pathogens

Parasites have evolved a wide range of mechanisms that they use to evade or manipulate the host's immune response and establish infection. The majority of the in vivo studies that have investigated these host-parasite interactions have been undertaken in experimental animals, especially rodents, which were housed and maintained to a high microbiological status. However, in the field situation it is increasingly apparent that pathogen co-infections within the same host are a common occurrence. For example, chronic infection with pathogens including malarial parasites, soil-transmitted helminths, Mycobacterium tuberculosis and viruses such as HIV may affect a third of the human population of some developing countries. Increasing evidence shows that co-infection with these pathogens may alter susceptibility to other important pathogens, and/or influence vaccine efficacy through their effects on host immune responsiveness. Co-infection with certain pathogens may also hinder accurate disease diagnosis. This review summarizes our current understanding of how the host's immune response to infection with different types of parasites can influence susceptibility to infection with other pathogenic microorganisms. A greater understanding of how infectious disease susceptibility and pathogenesis can be influenced by parasite co-infections will enhance disease diagnosis and the design of novel vaccines or therapeutics to more effectively control the spread of infectious diseases.

Helminth parasites and immune regulation

Helminth parasites are complex metazoans that belong to different taxonomic families but that collectively share the capacity to downregulate the host immune response directed toward themselves (parasite-specific immunoregulation). During long-standing chronic infection, these helminths appear able to suppress immune responses to bystander pathogens/antigens and atopic, autoimmune, and metabolic disorders. Helminth-induced immunoregulation occurs through the induction of regulatory T cells or Th2-type cells (or both). However, secreted or excreted parasite metabolites, proteins, or extracellular vesicles (or a combination of these) may also directly induce signaling pathways in host cells. Therefore, the focus of this review will be to highlight recent advances in understanding the immune responses to helminth infection, emphasizing the strategies/molecules and some of the mechanisms used by helminth parasites to modulate the immune response of their hosts.

Plasmodium and intestinal parasite perturbations of the infected host's inflammatory responses: a systematic review

Co-infection of malaria and intestinal parasites is widespread in sub-Saharan Africa and causes severe disease especially among the poorest populations. It has been shown that an intestinal parasite (helminth), mixed intestinal helminth or Plasmodium parasite infection in a human induces a wide range of cytokine responses, including anti-inflammatory, pro-inflammatory as well as regulatory cytokines. Although immunological interactions have been suggested to occur during a concurrent infection of helminths and Plasmodium parasites, different conclusions have been drawn on the influence this co-infection has on cytokine production. This review briefly discusses patterns of selected cytokine (IL-6, IL-8, IL-10, TNF-α and INF-γ) responses associated with infections caused by Plasmodium, intestinal parasites as well as a Plasmodium-helminth co-infection.

Seroepidemiology of helminths and the association with severe malaria among infants and young children in Tanzania

The disease burden of Wuchereria bancrofti and Plasmodium falciparum malaria is high, particularly in Africa, and co-infection is common. However, the effects of filarial infection on the risk of severe malaria are unknown. We used the remaining serum samples from a large cohort study in Muheza, Tanzania to describe vector-borne filarial sero-reactivity among young children and to identify associations between exposure to filarial parasites and subsequent severe malaria infections. We identified positive filarial antibody responses (as well as positive antibody responses to Strongyloides stercoralis) among infants as young as six months. In addition, we found a significant association between filarial seropositivity at six months of age and subsequent severe malaria. Specifically, infants who developed severe malaria by one year of age were 3.9 times more likely (OR = 3.9, 95% CI: 1.2, 13.0) to have been seropositive for filarial antigen at six months of age compared with infants who did not develop severe malaria.

Long-term Maintenance of CD4 T Cell Memory Responses to Malaria Antigens in Malian Children Coinfected with Schistosoma haematobium

Polyparasitism is common in the developing world. We have previously demonstrated that schistosomiasis-positive (SP) Malian children, aged 4-8 years, are protected from malaria compared to matched schistosomiasis-negative (SN) children. The effect of concomitant schistosomiasis upon acquisition of T cell memory is unknown. We examined antigen-specific T cell frequencies in 48 Malian children aged 4-14 to a pool of malaria blood stage antigens, and a pool of schistosomal antigens, at a time point during a malaria episode and at a convalescent time point ~6 months later, following cessation of malaria transmission. CD4+ T cell-derived memory responses, defined as one or more significant cytokine (IFN-γ, TNF-α, IL-2, and/or IL-17A) responses, was measured to schistoma antigens in 18/23 SP children at one or both time points, compared to 4/23 SN children (P < 0.0001). At the time of malaria infection, 12/24 SN children and 15/23 SP children (P = 0.29) stimulated with malaria antigens demonstrated memory recall as defined by CD4-derived cytokine production. This compares to 7/23 SN children and 16/23 SP children (P = 0.009) at the convalescent timepoint. 46.2% of cytokine-producing CD4+ T cells expressed a single cytokine after stimulation with malaria antigen during the malaria episode. This fell to 40.9% at follow-up with a compensatory rise of multifunctional cytokine secretion over time, a phenomenon consistent with memory maturation. The majority (53.2-59.5%) of responses derived from CD45RA-CD62L- effector memory T cells with little variation in the phenotype depending upon the time point or the study cohort. We conclude that detectable T cell memory responses can be measured against both malaria and schistosoma antigens and that the presence of Schistosoma haematobium may be associated with long-term maintenance of T memory to malaria.

Immunopathological response of leukocytes against microfilariae and adult worms in white rats infected with Setaria cervi

AIM

Aim of this study was to see the immunopathological changes against the microfilariae (Mf) and adult worms of a bovine filarid, Setaria cervi in the tissues of vital organs of experimentally infected white rats. The effect of diethylcarbamazine (DEC) was also observed on the Mf, as leukocytes especially lymphocytes produce immunoglobulins which opsonize and increase the efficacy of DEC against circulating Mf. Effect of this drug was also assessed on liver enzymes in the microfilaremic rats.

MATERIALS AND METHODS

Microfilaremia was established by implanting adult worms intraperitoneally and by the infusion of Mf recovered from the uterus of gravid female worms. DEC was administered orally for six consecutive days in the rats having patent infection. Differential leukocyte count was recorded every 3rd day, and liver enzymes were estimated every 10th day in both treated and untreated rats. Pathological changes were observed in HE stained sections of vital organs where Mf or adult worms were trapped.

RESULTS

Destruction and reduction in microfilarial density were noticed in microfilaremic rats treated with DEC. Trapped Mf and embedded worms revealed heavy cellular infiltrations by defensive cells which surrounded and attached with the body surface of the Mf as well as adult worms for their destruction and piece meal clearance. Immune-mediated pathology was observed in the tissue sections of lungs, spleen, and liver. Liver enzymes were elevated during the period of higher parasitemia.

CONCLUSIONS

There was a moderate level of immunopathology against the Mf and adult worms by the leukocytes in experimentally infected microfilaremic rats. Mf were in the process of degeneration where they got trapped. Moderate increase in liver enzyme was noticed which was slightly more in untreated group. Although a fraction of Mf gets killed in the peritoneum, majority of them successfully enter the systemic circulation and survive for about 54 days, which is sufficient enough for conducting immunological and chemotherapeutic studies.

Recognition of Plasmodium falciparum mature gametocyte-infected erythrocytes by antibodies of semi-immune adults and malaria-exposed children from Gabon

BACKGROUND

Transmission of malaria from man to mosquito depends on the presence of gametocytes, the sexual stage of Plasmodium parasites in the infected host. Naturally acquired antibodies against gametocytes exist and may play a role in controlling transmission by limiting the gametocyte development in the circulation or by interrupting gamete development and fertilization in the mosquito following ingestion. So far, most studies on antibody responses to sexual stage antigens have focused on a subset of gametocyte-surface antigens, even though inhibitory Ab responses to other gametocyte antigens might also play a role in controlling gametocyte density and fertility. Limited information is available on natural antibody response to the surfaces of gametocyte-infected erythrocytes.

METHODS

Ab responses to surface antigens of erythrocytes infected by in vitro differentiated Plasmodium falciparum mature gametocytes were investigated in sera of semi-immune adults and malaria-exposed children. In addition, the effect of immunization with GMZ2, a blood stage malaria vaccine candidate, and the effect of intestinal helminth infection on the development of immunity to gametocytes of P. falciparum was evaluated in malaria-exposed children and adults from Gabon. Serum samples from two Phase I clinical trials conducted in Gabon were analysed by microscopic and flow-cytometric immunofluorescence assay.

RESULTS

Adults had a higher Ab response compared to children. Ab reactivity was significantly higher after fixation and permeabilization of parasitized erythrocytes. Following vaccination with the malaria vaccine candidate GMZ2, anti-gametocyte Ab concentration decreased in adults compared to baseline. Ab response to whole asexual stage antigens had a significant but weak positive correlation to anti-gametocyte Ab responses in adults, but not in children. Children infected with Ascaris lumbricoides had a significantly higher anti-gametocyte Ab response compared to non-infected children.

CONCLUSION

The current data suggest that antigens exposed on the gametocyte-infected red blood cells are recognized by serum antibodies from malaria-exposed children and semi-immune adults. This anti-gametocyte immune response may be influenced by natural exposure and vaccination. Modulation of the natural immune response to gametocytes by co-infecting parasites should be investigated further and may have an important impact on malaria control strategies.

Schistosoma mansoni Infection Can Jeopardize the Duration of Protective Levels of Antibody Responses to Immunizations against Hepatitis B and Tetanus Toxoid

BACKGROUND

Schistosomiasis is a disease of major public health importance in sub-Saharan Africa. Immunoregulation begins early in schistosome infection and is characterized by hyporesponsiveness to parasite and bystander antigens, suggesting that a schistosome infection at the time of immunization could negatively impact the induction of protective vaccine responses. This study examined whether having a Schistosoma mansoni infection at the time of immunization with hepatitis B and tetanus toxoid (TT) vaccines impacts an individual's ability to achieve and maintain protective antibody levels against hepatitis B surface antigen or TT.

METHODS

Adults were recruited from Kisumu Polytechnic College in Western Kenya. At enrollment, participants were screened for schistosomiasis and soil transmitted helminths (STHs) and assigned to groups based on helminth status. The vaccines were then administered and helminth infections treated a week after the first hepatitis B boost. Over an 8 month period, 3 blood specimens were obtained for the evaluation of humoral and cytokine responses to the vaccine antigens and for immunophenotyping.

RESULTS

146 individuals were available for final analysis and 26% were S. mansoni positive (Sm+). Schistosomiasis did not impede the generation of initial minimum protective antibody levels to either hepatitis B or TT vaccines. However, median hepatitis B surface antibody levels were significantly lower in the Sm+ group after the first boost and remained lower, but not significantly lower, following praziquantel (PZQ) treatment and final boost. In addition, 8 months following TT boost and 7 months following PZQ treatment, Sm+ individuals were more likely to have anti-TT antibody levels fall below levels considered optimal for long term protection. IL-5 levels in response to in vitro TT stimulation of whole blood were significantly higher in the Sm+ group at the 8 month time period as well.

CONCLUSIONS

Individuals with schistosomiasis at the start the immunizations were capable of responding appropriately to the vaccines as measured by antibody responses. However, they may be at risk of a more rapid decline in antibody levels over time, suggesting that treating schistosome infections with praziquantel before immunizations could be beneficial. The timing of the treatment as well as its full impact on the maintenance of antibodies against vaccine antigens remains to be elucidated.

Community deworming alleviates geohelminth-induced immune hyporesponsiveness

In cross-sectional studies, chronic helminth infections have been associated with immunological hyporesponsiveness that can affect responses to unrelated antigens. To study the immunological effects of deworming, we conducted a cluster-randomized, double-blind, placebo-controlled trial in Indonesia and assigned 954 households to receive albendazole or placebo once every 3 mo for 2 y. Helminth-specific and nonspecific whole-blood cytokine responses were assessed in 1,059 subjects of all ages, whereas phenotyping of regulatory molecules was undertaken in 121 school-aged children. All measurements were performed before and at 9 and 21 mo after initiation of treatment. Anthelmintic treatment resulted in significant increases in proinflammatory cytokine responses to Plasmodium falciparum-infected red blood cells (PfRBCs) and mitogen, with the largest effect on TNF responses to PfRBCs at 9 mo-estimate [95% confidence interval], 0.37 [0.21-0.53], P value over time (P_time) < 0.0001. Although the frequency of regulatory T cells did not change after treatment, there was a significant decline in the expression of the inhibitory molecule cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) on CD4⁺ T cells of albendazole-treated individuals, -0.060 [-0.107 to -0.013] and -0.057 [-0.105 to -0.008] at 9 and 21 mo, respectively; P_time = 0.017. This trial shows the capacity of helminths to up-regulate inhibitory molecules and to suppress proinflammatory immune responses in humans. This could help to explain the inferior immunological responses to vaccines and lower prevalence of inflammatory diseases in low- compared with high-income countries.

Associations Between Helminth Infections, Plasmodium falciparum Parasite Carriage and Antibody Responses to Sexual and Asexual Stage Malarial Antigens

Infections with helminths and Plasmodium spp. overlap in their geographical distribution. It has been postulated that helminth infections may influence malarial transmission by altering Plasmodium falciparum gametocytogenesis. This cross-sectional study assessed the effect of helminth infections on P. falciparum gametocyte carriage and on humoral immune responses to sexual stage antigens in Gabon. Schistosoma haematobium and filarial infections as well as P. falciparum asexual forms and gametocyte carriage were determined. The antibody responses measured were to sexual (Pfs230, Pfs48/45) and asexual P. falciparum antigens (AMA1, MSP1, and GLURP). A total of 287 subjects were included. The prevalence of microscopically detectable P. falciparum asexual parasites was higher in S. haematobium-infected subjects in comparison to their uninfected counterparts (47% versus 26%, P = 0.003), but this was not different when filarial infections were considered. Plasmodium falciparum gametocyte carriage was similar between Schistosoma- or filaria-infected and uninfected subjects. We observed a significant decrease of Pfs48/45 immunoglobulin G titer in S. haematobium-infected subjects (P = 0.037), whereas no difference was seen for Pfs230 antibody titer, nor for antibodies to AMA1, MSP1, or GLURP. Our findings suggest an effect of S. haematobium on antibody responses to some P. falciparum gametocyte antigens that may have consequences for transmission-blocking immunity.

Cytokine modulation of human blood viscosity from vivax malaria patients

Malaria is a major infectious disease in several countries and is caused by protozoa of the genus Plasmodium. In vivax malaria patients, inflammatory processes occur, as well as changes in cytokines and blood flow. The present study analyzed the cytokine modulation of blood viscosity from patients infected with Plasmodium vivax (P. vivax). Blood samples were collected from 42 non-infected individuals (control group) and 37 individuals infected with P. vivax. The IL-2, IL-4, IL-6, IL-10, TNFα, TGF-β and IL-17 cytokine concentrations in the serum were assessed, and the blood rheological properties were determined. The analysis of blood viscosity for shear rates revealed that the blood viscosity of the infected patients was significantly greater than that of the non-infected individuals. The viscosity of the blood was greater in the infected individuals than in the non-infected subjects. The serum from individuals with P. vivax infections exhibited higher IFN-γ and IL-17 concentrations and lower TGF-β levels. Incubation of the blood from infected individuals with IL-17 or IL-17 associated with IFN-γ reduced the viscosity to rates equivalent to the blood from non-infected individuals. Independently of cytokine modulation, no correlation was found between the parasitemia and blood viscosity of the infected patients. These data suggest that the alterations of blood viscosity are relevant as an auxiliary tool for the clinical diagnosis of disease. In malaria, erythrocytes are more sensitive to osmotic shock, and the reduction of viscosity by IL-17 may be related to a possible immunomodulator agent during infection.

Is the infectiousness of dogs naturally infected with Trypanosoma cruzi associated with poly-parasitism?

Interactions among different species of parasites co-infecting the same host could be synergistic or antagonistic. These interactions may modify both the frequency of infected hosts and their infectiousness, and therefore impact on transmission dynamics. This study determined the infectiousness of Trypanosoma cruzi-seropositive dogs (using xenodiagnosis) and their parasite load (quantified by qPCR), and tested the association between both variables and the presence of concomitant endoparasites. A cross-sectional serosurvey conducted in eight rural villages from Pampa del Indio and neighboring municipalities (northeastern Argentina) detected 32 T. cruzi-seropositive dogs out of 217 individuals examined for infection. Both the infectiousness to the vector Triatoma infestans and parasite load of T. cruzi-seropositive dogs examined were heterogeneous. A statistically significant, nine-fold higher mean infectiousness was registered in T. cruzi-seropositive dogs co-infected with Ancylostoma caninum and a trematode than in T. cruzi-seropositive dogs without these infections. The median parasite load of T. cruzi was also significantly higher in dogs co-infected with these helminths. An opposite trend was observed in T. cruzi-seropositive dogs that were serologically positive to Toxoplasma gondii or Neospora caninum relative to dogs seronegative for these parasites. Using multiple logistic regression analysis with random effects, we found a positive and significant association between the infectiousness of T. cruzi-seropositive dogs and co-infections with A. caninum and a trematode. Our results suggest that co-infections may be a modifier of host infectiousness in dogs naturally infected with T. cruzi.

Effects of Pregnancy-associated Malaria on T Cell Cytokines in Cameroonian Women

Although Th17 cells subsets improve immunity against extra and intracellular pathogens, and in modulating Th1 and other immune responses, its role on pregnancy-associated malaria (PAM) is unknown. This study aims to investigate the effects of PAM on Th1 (IFN-γ, TNF-α), IL-10 family (IL-10, IL-19, IL-22), Th17 (IL-17A, IL-23) cytokines and on CXCL-10 chemokine profiles in pregnant women. Between 2010 and 2011, venous blood specimens from 107 volunteer pregnant Cameroonian women was used to determine parasitaemia microscopically and haemoglobin levels using HemoCue analyzer. Plasma levels of the biomarkers were determined by ELISA. Parasitaemia was higher in women with low haemoglobin levels, parity and mother's age. IL-10 and CXCL-10 plasma levels were higher in the malaria infected and in anaemic women while IFN-γ and IL-17A levels were higher in malaria non-infected and in non-anaemic women. Parasitaemia correlated positively with IL-10 and CXCL-10 levels but inversely with IFN-γ and IL-17A. Haemoglobin levels were higher in women with low IL-10 and CXCL-10 levels, and in group with high IFN-γ, IL-17A and IL-23 levels. Only IL-10 levels associated negatively with parity. Positive correlations were observed between Th17 (IL-17A) and Th1 (IFN-γ, TNF-α), IL-10 family (IL-19 and IL-22) and Th17 (IL-23) cytokines. Multivariate analysis showed association between: mother's age and IFN-γ levels, parasitaemia and IL-10 and CXCL-10 levels and haemoglobin levels, gestational age and IL-17A levels. In conclusion, during PAM, CXCL-10 and IL-10 responses are implicated in the pathogenesis while Th17 and Th1 immune responses, via IL-17A and IFN-γ might play protective roles.

Reductions in microfilaridermia by repeated ivermectin treatment are associated with lower Plasmodium-specific Th17 immune responses in Onchocerca volvulus-infected individuals

BACKGROUND

37 million individuals are currently infected with Onchocerca volvulus (O. volvulus), a parasitic nematode that elicits various dermal manifestations and eye damage in man. Disease control is primarily based on distributing ivermectin in mass drug administration (MDA) programmes which aim at breaking transmission by eliminating microfilariae (MF), the worm's offspring. The majority of infected individuals present generalized onchocerciasis, which is characterized by hyporesponsive immune responses and high parasite burden including MF. Recently, in areas that have been part of MDA programmes, individuals have been identified that present nodules but are amicrofilaridermic (a-MF) and our previous study showed that this group has a distinct immune profile. Expanding on those findings we determined the immune responses of O. volvulus-infected individuals to a Plasmodium-derived antigen MSP-1 (merozoite surface protein-1), which is required by the parasite to enter erythrocytes.

METHODS

Isolated PBMCs from O. volvulus-infected individuals (164 MF(+) and 46 a-MF) and non-infected volunteers from the same region (NEN), were stimulated with MSP-1 and the resulting supernatant screened for the presence of IL-5, IL-13, IFN-γ, TNF-α, IL-6, IL-17A and IL-10. These findings were then further analyzed following regression analysis using the covariates MF, ivermectin (IVM) and region. The latter referred to the Central or Ashanti regions of Ghana, which, at the time sampling, had received 8 or 1 round of MDA respectively.

RESULTS

IL-5, IL-13 and IFN-γ responses to MSP-1 were not altered between NEN and O. volvulus-infected individuals nor were any associations revealed in the regression analysis. IL-10, IL-6 and TNF-α MSP-1 responses were, however, significantly elevated in cultures from infected individuals. Interestingly, when compared to a-MF individuals, MSP-induced IL-17A responses were significantly higher in MF(+) patients. Following multivariable regression analysis these IL-10, IL-6, TNF-α and IL-17A responses were all dominantly associated with the regional covariate.

CONCLUSIONS

Consequently, areas with a lowered infection pressure due to IVM MDA appear to influence bystander responses to Plasmodium-derived antigens in community members even if they have not regularly participated in the therapy.

Cytokine and chemokine profile of the innate and adaptive immune response of Schistosoma haematobium and Plasmodium falciparum single and co-infected school-aged children from an endemic area of Lambaréné, Gabon

BACKGROUND

Helminths and malaria are among the most prevalent infectious diseases in the world. They both occur in tropical area where they often affect the same populations. There are studies suggesting an effect of helminths on malariometric indices. For example, malaria attacks as well as disease severity has been shown to be influenced by a concurrent chronic helminth infection. However, there are also studies that show no effect of concurrent helminth infections on malarial outcomes. To start addressing this issue, the effect of chronic Schistosoma haematobium infection on both the innate and adaptive immune response of Plasmodium falciparum-infected subjects was assessed in an area endemic for both these infections in Gabon.

METHOD

Subjects infected with S. haematobium and or P. falciparum, as well as a control group with neither of these infections, were recruited. For innate immune response, heparinized blood was obtained and cultured for 24 hours with a panel of TLR ligands. For adaptive immune response, PBMC was isolated and stimulated with SEB for 72 hours. Cytokines and chemokines were measured in supernatants using a multiplex beads array immunoassay. Principal Component analysis was used to assess pattern of cytokine and chemokine responses representing the innate and adaptive components of the immune system.

RESULTS

Overall it was observed that the presence of P. falciparum infection was marked by an increase in innate and adaptive immune responsiveness while S. haematobium infection was characterized by an increased chemokine profile, with at the same time, lower pro inflammatory markers. When the study subjects were split into single infected and co-infected groups no effect of S. haematobium on the immune response of P. falciparum infected subjects was observed, neither for the innate nor for the adaptive component of the immune response.

CONCLUSION

This study provides original information on the cellular immune response of S. haematobium and/or P. falciparum in infected subjects. It rules out an effect of S. haematobium on the cytokine profile of subjects co-infected with P. falciparum.

CD4 T-cell subsets in malaria: TH1/TH2 revisited

CD4⁺ T-cells have been shown to play a central role in immune control of infection with Plasmodium parasites. At the erythrocytic stage of infection, IFN-γ production by CD4⁺ T-cells and CD4⁺ T-cell help for the B-cell response are required for control and elimination of infected red blood cells. CD4⁺ T-cells are also important for controlling Plasmodium pre-erythrocytic stages through the activation of parasite-specific CD8⁺ T-cells. However, excessive inflammatory responses triggered by the infection have been shown to drive pathology. Early classical experiments demonstrated a biphasic CD4⁺ T-cell response against erythrocytic stages in mice, in which T helper (Th)1 and antibody-helper CD4⁺ T-cells appear sequentially during a primary infection. While IFN-γ-producing Th1 cells do play a role in controlling acute infections, and they contribute to acute erythrocytic-stage pathology, it became apparent that a classical Th2 response producing IL-4 is not a critical feature of the CD4⁺ T-cell response during the chronic phase of infection. Rather, effective CD4⁺ T-cell help for B-cells, which can occur in the absence of IL-4, is required to control chronic parasitemia. IL-10, important to counterbalance inflammation and associated with protection from inflammatory-mediated severe malaria in both humans and experimental models, was originally considered be produced by CD4⁺ Th2 cells during infection. We review the interpretations of CD4⁺ T-cell responses during Plasmodium infection, proposed under the original Th1/Th2 paradigm, in light of more recent advances, including the identification of multifunctional T-cells such as Th1 cells co-expressing IFN-γ and IL-10, the identification of follicular helper T-cells (Tfh) as the predominant CD4⁺ T helper subset for B-cells, and the recognition of inherent plasticity in the fates of different CD4⁺ T-cells.

Role of some biomarkers in placental malaria in women living in Yaoundé, Cameroon

Despite intensive research on the immunpathology of placental malaria (PM), the role of some β-chemokines known to attract inflammatory cells is less known. This study sought to determine the role of CXCL-10, IL-10, IL-19, IL-17A and IL-23 in placental malaria in women at delivery. Between 2010 and 2011, paired peripheral and placental blood specimens were collected from 139 Cameroonian women at delivery. Differential white blood cell counts and malaria parasitaemia were determined microscopically while the accumulation of parasites in the placenta was investigated through histological studies. Plasma levels of CXCL-10, IL-10, IL-17A, IL-19 and Il-23 were determined by ELISA. The cytokines IL-10, IL-17A and IL-23 were predominant in peripheral plasma from both infected and non-infected women. While IL-10 associated negatively with parity, IL-23 showed a positive correlation (p<0.05). The production of CXCL-10 was independent of parity and higher in placental plasma. There was an association between the plasma levels of IL-10 and CXCL-10 with malaria parasitaemia in the placenta impression smears, placental and peripheral blood and the presence of malaria pigments in the placenta tissue. Leukocyte accumulation into the intervillous space correlated positively with plasma levels of placental IL-17A (p<0.001). Parity also associated with peripheral IL-17A (p=0.016). The peripheral and placental plasma levels of CXCL-10 and IL-10 also correlated positively with monocyte counts (p=0.011-0.042) while a negative correlation was found with lymphocyte counts (p=0.017 to <0.001) of the impression smear. However, the levels of IL-10 in both peripheral and placental plasma and CXCL-10 in placental plasma only, were higher in low birth weight baby. With regards to IL-17A, its placental plasma level correlated positively with lymphocyte counts of placental blood (p=0.045). During PM, CXCL-10 might attract monocytes and lymphocytes into the placenta where they produce inflammatory cytokines such as IL-10 and IL-17A to modulate the disease, which affect baby weight.

Helminths in the lungs

Parasitic helminths infect well over one billion people and typically cause chronic and recurrent infections that exert a considerable toll on human health and productivity. A significant number of important intestinal- and tissue-dwelling helminth parasites have evolved a scripted migration through select organ systems. Of specific interest here are the helminth parasites that interact with respiratory tissues and the pulmonary immune system. This review will consider the nature of the interactions between helminth parasites and the lung environment, as well as the consequences of these interactions on the evolution of parasitism and host immunity.

Vaccination against helminth parasite infections

Helminth parasites infect over one fourth of the human population and are highly prevalent in livestock worldwide. In model systems, parasites are strongly immunomodulatory, but the immune system can be driven to expel them by prior vaccination. However, no vaccines are currently available for human use. Recent advances in vaccination with recombinant helminth antigens have been successful against cestode infections of livestock and new vaccines are being tested against nematode parasites of animals. Numerous vaccine antigens are being defined for a wide range of helminth parasite species, but greater understanding is needed to define the mechanisms of vaccine-induced immunity, to lay a rational platform for new vaccines and their optimal design. With human trials underway for hookworm and schistosomiasis vaccines, a greater integration between veterinary and human studies will highlight the common molecular and mechanistic pathways, and accelerate progress towards reducing the global health burden of helminth infection.

Parasite virulence, co-infections and cytokine balance in malaria

Strong early inflammatory responses followed by a timely production of regulatory cytokines are required to control malaria parasite multiplication without inducing major host pathology. Here, we briefly examine the homeostasis of inflammatory responses to malaria parasite species with varying virulence levels and discuss how co-infections with bacteria, viruses, and helminths can modulate inflammation, either aggravating or alleviating malaria-related morbidity.

Highly heterogeneous, activated, and short-lived regulatory T cells during chronic filarial infection

The mechanisms underlying the increase in the numbers of regulatory T (Treg) cells in chronic infection settings remain unclear. Here we have delineated the phenotype and transcriptional profiles of Treg cells from 18 filarial-infected (Fil(+) ) and 19 filarial-uninfected (Fil(-) ) subjects. We found that the frequencies of Foxp3(+) Treg cells expressing CTLA-4, GITR, LAG-3, and IL-10 were significantly higher in Fil(+) subjects compared with that in Fil(-) subjects. Foxp3-expressing Treg-cell populations in Fil(+) subjects were also more heterogeneous and had higher expression of IL-10, CCL-4, IL-29, CTLA-4, and TGF-β than Fil(-) subjects, each of these cytokines having been implicated in immune suppression. Moreover, Foxp3-expressing Treg cells from Fil(+) subjects had markedly upregulated expression of activation-induced apoptotic genes with concomitant downregulation of those involved in cell survival. To determine whether the expression of apoptotic genes was due to Treg-cell activation, we found that the expression of CTLA-4, CDk8, RAD50, TNFRSF1A, FOXO3, and RHOA were significantly upregulated in stimulated cells compared with unstimulated cells. Taken together, our results suggest that in patent filarial infection, the expanded Treg-cell populations are heterogeneous, short-lived, activated, and express higher levels of molecules known to modulate immune responsiveness, suggesting that filarial infection is associated with high Treg-cell turnover.

Co-infection restrains Litomosoides sigmodontis filarial load and plasmodial P. yoelii but not P. chabaudi parasitaemia in mice

Infection with multiple parasite species is clearly the norm rather than the exception, in animals as well as in humans. Filarial nematodes and Plasmodium spp. are important parasites in human public health and they are often co-endemic. Interactions between these parasites are complex. The mechanisms underlying the modulation of both the course of malaria and the outcome of filarial infection are poorly understood. Despite increasing activity in recent years, studies comparing co- and mono-infections are very much in their infancy and results are contradictory at first sight. In this study we performed controlled and simultaneous co-infections of BALB/c mice with Litomosoides sigmodontis filaria and with Plasmodium spp. (Plasmodium yoelii 17 XNL or Plasmodium chabaudi 864VD). An analysis of pathological lesions in the kidneys and lungs and a parasitological study were conducted at different times of infection. Whatever the plasmodial species, the filarial recovery rate was strongly decreased. The peak of parasitaemia in the plasmodial infection was decreased in the course of P. yoelii infection but not in that of P. chabaudi. Regarding pathological lesions, L. sigmodontis can reverse lesions in the kidneys due to the presence of both Plasmodium species but does not modify the course of pulmonary lesions. The filarial infection induces granulomas in the lungs.

IFNγ/IL-10 co-producing cells dominate the CD4 response to malaria in highly exposed children

Although evidence suggests that T cells are critical for immunity to malaria, reliable T cell correlates of exposure to and protection from malaria among children living in endemic areas are lacking. We used multiparameter flow cytometry to perform a detailed functional characterization of malaria-specific T cells in 78 four-year-old children enrolled in a longitudinal cohort study in Tororo, Uganda, a highly malaria-endemic region. More than 1800 episodes of malaria were observed in this cohort, with no cases of severe malaria. We quantified production of IFNγ, TNFα, and IL-10 (alone or in combination) by malaria-specific T cells, and analyzed the relationship of this response to past and future malaria incidence. CD4⁺ T cell responses were measurable in nearly all children, with the majority of children having CD4⁺ T cells producing both IFNγ and IL-10 in response to malaria-infected red blood cells. Frequencies of IFNγ/IL10 co-producing CD4⁺ T cells, which express the Th1 transcription factor T-bet, were significantly higher in children with ≥2 prior episodes/year compared to children with <2 episodes/year (P<0.001) and inversely correlated with duration since malaria (Rho = −0.39, P<0.001). Notably, frequencies of IFNγ/IL10 co-producing cells were not associated with protection from future malaria after controlling for prior malaria incidence. In contrast, children with <2 prior episodes/year were significantly more likely to exhibit antigen-specific production of TNFα without IL-10 (P = 0.003). While TNFα-producing CD4⁺ T cells were not independently associated with future protection, the absence of cells producing this inflammatory cytokine was associated with the phenotype of asymptomatic infection. Together these data indicate that the functional phenotype of the malaria-specific T cell response is heavily influenced by malaria exposure intensity, with IFNγ/IL10 co-producing CD4⁺ T cells dominating this response among highly exposed children. These CD4⁺ T cells may play important modulatory roles in the development of antimalarial immunity.

Despite reports of decreasing malaria morbidity across many parts of Africa, the incidence of malaria among children continues to be very high in Uganda, even in the setting of insecticide-treated bednets and artemisinin-based combination therapy. Additional control measures, including a vaccine, are sorely needed in these settings, but progress has been limited by our lack of understanding of immunologic correlates of exposure and protection. T cell responses to malaria are thought to be important for protection in experimental models, but their role in protecting against naturally acquired infection is not clear. In this study, we performed detailed assessments of the malaria-specific T cell response among 4-year-old children living in Tororo, Uganda, an area of high malaria transmission. We found that recent malaria infection induces a malaria-specific immune response dominated by Th1 T cells co-producing IFNγ and IL-10, and that these cells are not associated with protection from future infection. IFNγ/IL-10 co-producing cells have been described in several parasitic infections and are hypothesized to be important in limiting CD4-mediated pathology, but they may also prevent the development of sterilizing immunity. These observations have important implications for understanding the pathophysiology of malaria in humans and for malaria vaccine development.

Recent progress in host immunity to avian coccidiosis: IL-17 family cytokines as sentinels of the intestinal mucosa

The molecular and cellular mechanisms leading to immune protection against coccidiosis are complex and include multiple aspects of innate and adaptive immunities. Innate immunity is mediated by various subpopulations of immune cells that recognize pathogen associated molecular patterns (PAMPs) through their pattern recognition receptors (PRRs) leading to the secretion of soluble factors with diverse functions. Adaptive immunity, which is important in conferring protection against subsequent reinfections, involves subtypes of T and B lymphocytes that mediate antigen-specific immune responses. Recently, global gene expression microarray analysis has been used in an attempt to dissect this complex network of immune cells and molecules during avian coccidiosis. These new studies emphasized the uniqueness of the innate immune response to Eimeria infection, and directly led to the discovery of previously uncharacterized host genes and proteins whose expression levels were modulated following parasite infection. Among these is the IL-17 family of cytokines. This review highlights recent progress in IL-17 research in the context of host immunity to avian coccidiosis.

Regulatory T cell subsets in filarial infection and their function

Filarial infections in humans are chronic infections that cause significant morbidity. The chronic nature of these infections with continuous antigen release is associated with a parasite-specific T cell hypo-responsiveness that may over time also affect the immune responses to bystander antigens. Previous studies have shown the filarial parasite antigen-specific T cells hypo-responsiveness is mediated by regulatory cytokines – IL-10 and TGF-β in particular. Recent studies have suggested that the modulated/regulated T cell responses associated with patent filarial infection may reflect an expansion of regulatory T cells (Tregs) that include both Tregs induced in peripheral circulation or pTregs and the thymus-derived Tregs or tTregs. Although much is known about the phenotype of these regulatory populations, the mechanisms underlying their expansion and their mode of action in filarial and other infections remain unclear. Nevertheless there are data to suggest that while many of these regulatory cells are activated in an antigen-specific manner the ensuing effectors of this activation are relatively non-specific and may affect a broad range of immune cells. This review will focus on the subsets and function of regulatory T cells in filarial infection.

Decreased prevalence of sepsis but not mild or severe P. falciparum malaria is associated with pre-existing filarial infection

Background

Enhanced inflammatory host responses have been attributed as the cellular basis for development of severe malaria as well as sepsis. In contrast to this, filarial infections have been consistently reported to be associated with an immunological hypo-responsive phenotype. This suggests that successful control of filariasis by employing mass drug administration, could potentially contribute to an increase in incidence of sepsis and cerebral malaria in human communities. A case control study was undertaken to address this critical and urgent issue.

Methods

Eighty-nine patients with sepsis and one hundred and ninety-six patients with P. falciparum malaria all originating from Odisha, were tested for prevalence of circulating filarial antigens - a quantitative marker of active filarial infection. Antibodies to four stage specific malarial recombinant proteins were measured by solid phase immunoassays and circulating CD4+CD25^high T-cells were quantified by flow cytometry with an objective to study if pre-existing filarial infections influence antibody responses to malarial antigens or the levels of circulating T-regulatory cells in P. falciparum infected patients.

Results

Prevalence of filarial antigenemia was significantly less in sepsis patients as compared to controls suggesting that pre-existing filariasis could influence development of sepsis. On the other hand, levels of circulating filarial antigen were comparable in severe malaria cases and healthy controls suggesting that development of severe malaria is independent of pre-existing W. bancrofti infections. Plasma TNF-a, RANTES and antibodies to recombinant malarial proteins as well as levels of circulating CD4+ CD25^high cells were comparable in malaria patients with or without filarial infections.

Conclusions

These observations imply that successful control of filariasis could have adverse consequences on public health by increasing the incidence of sepsis, while the incidence of severe malaria may not adversely increase as a consequence of elimination of filariasis.

Immunomodulation in Plasmodium falciparum malaria: experiments in nature and their conflicting implications for potential therapeutic agents

Effective Plasmodium falciparum immunity requires a precisely timed and balanced response of inflammatory and anti-inflammatory immune regulators. These responses begin with innate immune effectors and are modulated over the course of an infection and between episodes to limit inflammation. To date, there are no effective immunomodulatory therapies for severe malaria. Some of the most potent immunomodulators are naturally occurring infections, including helminthic and chronic viral infections. This review examines malaria coinfection with these organisms, and their impact on malaria morbidity and immune responses. Overall, there is compelling evidence to suggest that chronic coinfections can modulate deleterious malaria-specific immune responses, suggesting that therapeutic agents may be effective if utilized early in infection. Examination of the mechanisms of these effects may serve as a platform to identify more targeted and effective malaria immunomodulatory therapeutics.

Helminth infection in populations undergoing epidemiological transition: a friend or foe?

Helminth infections are highly prevalent in developing countries, especially in rural areas. With gradual development, there is a transition from living conditions that are dominated by infection, poor sanitation, manual labor, and traditional diet to a situation where burden of infections is reduced, infrastructure is improved, sedentary lifestyle dominates, and processed food forms a large proportion of the calorie intake. The combinations of some of the changes in lifestyle and environment are expected to result in alteration of the landscape of diseases, which will become dominated by non-communicable disorders. Here we review how the major helminth infections affect a large proportion of the population in the developing world and discuss their impact on the immune system and the consequences of this for other infections which are co-endemic in the same areas. Furthermore, we address the issue of decreasing helminth infections in many parts of the world within the context of increasing inflammatory, metabolic, and cardiovascular diseases.

Filariasis attenuates anemia and proinflammatory responses associated with clinical malaria: a matched prospective study in children and young adults

Background

Wuchereria bancrofti (Wb) and Mansonella perstans (Mp) are blood-borne filarial parasites that are endemic in many countries of Africa, including Mali. The geographic distribution of Wb and Mp overlaps considerably with that of malaria, and coinfection is common. Although chronic filarial infection has been shown to alter immune responses to malaria parasites, its effect on clinical and immunologic responses in acute malaria is unknown.

Methodology/Principal Findings

To address this question, 31 filaria-positive (FIL+) and 31 filaria-negative (FIL−) children and young adults, matched for age, gender and hemoglobin type, were followed prospectively through a malaria transmission season. Filarial infection was defined by the presence of Wb or Mp microfilariae on calibrated thick smears performed between 10 pm and 2 am and/or by the presence of circulating filarial antigen in serum. Clinical malaria was defined as axillary temperature ≥37.5°C or another symptom or sign compatible with malaria infection plus the presence of asexual malaria parasites on a thick blood smear. Although the incidence of clinical malaria, time to first episode, clinical signs and symptoms, and malaria parasitemia were comparable between the two groups, geometric mean hemoglobin levels were significantly decreased in FIL− subjects at the height of the transmission season compared to FIL+ subjects (11.4 g/dL vs. 12.5 g/dL, p<0.01). Plasma levels of IL-1ra, IP-10 and IL-8 were significantly decreased in FIL+ subjects at the time of presentation with clinical malaria (99, 2145 and 49 pg/ml, respectively as compared to 474, 5522 and 247 pg/ml in FIL− subjects).

Conclusions/Significance

These data suggest that pre-existent filarial infection attenuates immune responses associated with severe malaria and protects against anemia, but has little effect on susceptibility to or severity of acute malaria infection. The apparent protective effect of filarial infection against anemia is intriguing and warrants further study in a larger cohort.

In many regions of the world, including sub-Saharan Africa, concomitant infection with multiple parasites is common. In order to examine the effects of filariasis, a chronic helminth infection, on immune responses and clinical manifestations of acute malaria infection, the authors followed 31 filaria-infected (FIL+) and 31 filaria-uninfected (FIL–) individuals living in a malaria-endemic area of Mali through an entire malaria transmission season for the development of clinical malaria (fever or other symptoms of malaria in the setting of detectable blood parasites). Serum levels of inflammatory cytokines previously associated with severe malaria were decreased in FIL+ subjects at the time of acute clinical malaria. Although there were no differences between FIL+ and FIL– subjects with respect to the time of first episode of malaria or the number or severity of malaria episodes, filarial infection appeared to protect against the development of anemia during the malaria transmission season. These findings demonstrate that chronic filarial infection modulates the immune response to acute malaria. The apparent effect on anemia is intriguing and deserves further study.

Malaria and lymphatic filariasis: the case for integrated vector management

The global programmes to eliminate both malaria and lymphatic filariasis are facing operational and technical challenges. Available data show that the use of treated or untreated bednets and indoor residual spraying for malaria control concomitantly reduced filarial rates. In turn, mass drug administration campaigns against lymphatic filariasis can be combined with the distribution of insecticide-treated bednets. Combining these disease control efforts could lead to more efficient use of resources, more accurate attribution of effects, and more effective control of both diseases. Systematic integration requires coordination at all levels, mapping of coendemic areas, and comprehensive monitoring and evaluation.

Helminth infections and host immune regulation

Helminth parasites infect almost one-third of the world's population, primarily in tropical regions. However, regions where helminth parasites are endemic record much lower prevalences of allergies and autoimmune diseases, suggesting that parasites may protect against immunopathological syndromes. Most helminth diseases are spectral in nature, with a large proportion of relatively asymptomatic cases and a subset of patients who develop severe pathologies. The maintenance of the asymptomatic state is now recognized as reflecting an immunoregulatory environment, which may be promoted by parasites, and involves multiple levels of host regulatory cells and cytokines; a breakdown of this regulation is observed in pathological disease. Currently, there is much interest in whether helminth-associated immune regulation may ameliorate allergy and autoimmunity, with investigations in both laboratory models and human trials. Understanding and exploiting the interactions between these parasites and the host regulatory network are therefore likely to highlight new strategies to control both infectious and immunological diseases.

Differential induction of Th2- and Th1-associated responses by filarial antigens and endosymbiotic Wolbachia in a murine model of river blindness

Immune responses to filarial parasites like the river blindness inducing Onchocerca volvulus are obscured by combined reactions to the filarial nematodes themselves and their endosymbiont bacteria Wolbachia. Overall, infection with filarial nematodes induces a strong Th2 response characterized by IL-5 production and to a lesser degree a Th1 response and IFNγ production. Neutrophil and eosinophil infiltration into the corneal stroma are hallmark features of Onchocerca volvulus stimulation in a mouse model of river blindness. To determine the splenic and corneal response to filarial antigens in the absence of Wolbachia, C57BL/6 mice were immunized subcutaneously with either endosymbiotic Wolbachia alone, a soluble extract from the filaria Acanthocheilonema viteae that does not contain Wolbachia, or both, and injected into the corneal stroma. Neutrophil and eosinophil infiltration into the cornea was assessed by immunohistochemistry. In addition, Th1- and Th2-associated responses to filaria or Wolbachia were investigated by determining IL-5 and IFN-γ production by splenocytes. We found that A. viteae in the absence of Wolbachia induced IL-5 production and eosinophil infiltration, but not IFN-γ. Conversely, Wolbachia induced IFN-γ production and no migration of eosinophils. There was no difference in neutrophil infiltration. Together, these findings demonstrate a distinct Th-associated phenotype induced by filaria and Wolbachia.