Malaria parasites require TLR9 signaling for immune evasion by activating regulatory T cells

The ultimate tradeoff: how red cell adaptations to malaria alter the host response during critical illness

The human immune system evolved in response to pathogens. Among these pathogens, malaria has proven to be one of the deadliest and has exerted the most potent selective pressures on its target cell, the red blood cell. Red blood cells have recently gained recognition for their immunomodulatory properties, yet how red cell adaptations contribute to the host response during critical illness remains understudied. This review will discuss how adaptations that may have been advantageous for host survival might influence immune responses in modern critical illness. We will highlight the current evidence for divergent host resilience arising from the adaptations to malaria and summarize how understanding evolutionary red cell adaptations to malaria may provide insight into the heterogeneity of the host response to critical illness, perhaps driving future precision medicine approaches to syndromes affecting the critically ill such as sepsis and acute respiratory distress syndrome (ARDS).

Newborn DNA methylation and asthma acquisition across adolescence and early adulthood

BACKGROUND

Little is known about the association of newborn DNA methylation (DNAm) with asthma acquisition across adolescence and early adult life.

OBJECTIVE

We aim to identify epigenetic biomarkers in newborns for asthma acquisition during adolescence or young adulthood.

METHODS

The Isle of Wight Birth Cohort (IOWBC) (n = 1456) data at ages 10, 18 and 26 years were assessed. To screen cytosine-phosphate-guanine site (CpGs) potentially associated with asthma acquisition, at the genome scale, we examined differentially methylated regions (DMR) using dmrff R package and individual CpG sites using linear regression on such associations. For CpGs that passed screening, we examined their enrichment in biological pathways using their mapping genes and tested their associations with asthma acquisitions using logistic regressions. Findings in IOWBC were tested in an independent cohort, the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort.

RESULTS

In total, 2636 unique CpGs passed screening, based on which we identified one biological pathway linked to asthma acquisition during adolescence in females (FDR adjusted p-value = .003 in IOWBC). Via logistic regressions, for females, four CpGs were shown to be associated with asthma acquisition during adolescence, and another four CpGs with asthma acquisition in young adulthood (FDR adjusted p-value < .05 in IOWBC) and these eight CpGs were replicated in ALSPAC (all p-values < .05). DNAm at all the identified CpGs was shown to be temporally consistent, and at six of the CpGs was associated with expressions of adjacent or mapping genes in females (all p-values < .05). For males, 622 CpGs were identified in IOWBC (FDR = 0.01), but these were not tested in ALSPAC due to small sample sizes.

CONCLUSION AND CLINICAL RELEVANCE

Eight CpGs on LHX5, IL22RA2, SOX11, CBX4, ACPT, CFAP46, MUC4, and ATP1B2 genes have the potential to serve as candidate epigenetic biomarkers in newborns for asthma acquisition in females during adolescence or young adulthood.

Crosstalk of Microorganisms and Immune Responses in Autoimmune Neuroinflammation: A Focus on Regulatory T Cells

Regulatory T cells (Tregs) are the major determinant of peripheral immune tolerance. Many Treg subsets have been described, however thymus-derived and peripherally induced Tregs remain the most important subpopulations. In multiple sclerosis, a prototypical autoimmune disorder of the central nervous system, Treg dysfunction is a pathogenic hallmark. In contrast, induction of Treg proliferation and enhancement of their function are central immune evasion mechanisms of infectious pathogens. In accordance, Treg expansion is compartmentalized to tissues with high viral replication and prolonged in chronic infections. In friend retrovirus infection, Treg expansion is mainly based on excessive interleukin-2 production by infected effector T cells. Moreover, pathogens seem also to enhance Treg functions as shown in human immunodeficiency virus infection, where Tregs express higher levels of effector molecules such as cytotoxic T-lymphocyte-associated protein 4, CD39 and cAMP and show increased suppressive capacity. Thus, insights into the molecular mechanisms by which intracellular pathogens alter Treg functions might aid to find new therapeutic approaches to target central nervous system autoimmunity. In this review, we summarize the current knowledge of the role of pathogens for Treg function in the context of autoimmune neuroinflammation. We discuss the mechanistic implications for future therapies and provide an outlook for new research directions.

Lessons Learned for Pathogenesis, Immunology, and Disease of Erythrocytic Parasites: Plasmodium and Babesia

Malaria caused by Plasmodium species and transmitted by Anopheles mosquitoes affects large human populations, while Ixodes ticks transmit Babesia species and cause babesiosis. Babesiosis in animals has been known as an economic drain, and human disease has also emerged as a serious healthcare problem in the last 20–30 years. There is limited literature available regarding pathogenesis, immunity, and disease caused by Babesia spp. with their genomes sequenced only in the last decade. Therefore, using previous studies on Plasmodium as the foundation, we have compared similarities and differences in the pathogenesis of Babesia and host immune responses. Sexual life cycles of these two hemoparasites in their respective vectors are quite similar. An adult Anopheles female can take blood meal several times in its life such that it can both acquire and transmit Plasmodia to hosts. Since each tick stage takes blood meal only once, transstadial horizontal transmission from larva to nymph or nymph to adult is essential for the release of Babesia into the host. The initiation of the asexual cycle of these parasites is different because Plasmodium sporozoites need to infect hepatocytes before egressed merozoites can infect erythrocytes, while Babesia sporozoites are known to enter the erythrocytic cycle directly. Plasmodium metabolism, as determined by its two- to threefold larger genome than different Babesia, is more complex. Plasmodium replication occurs in parasitophorous vacuole (PV) within the host cells, and a relatively large number of merozoites are released from each infected RBC after schizogony. The Babesia erythrocytic cycle lacks both PV and schizogony. Cytoadherence that allows the sequestration of Plasmodia, primarily P. falciparum in different organs facilitated by prominent adhesins, has not been documented for Babesia yet. Inflammatory immune responses contribute to the severity of malaria and babesiosis. Antibodies appear to play only a minor role in the resolution of these diseases; however, cellular and innate immunity are critical for the clearance of both pathogens. Inflammatory immune responses affect the severity of both diseases. Macrophages facilitate the resolution of both infections and also offer cross-protection against related protozoa. Although the immunosuppression of adaptive immune responses by these parasites does not seem to affect their own clearance, it significantly exacerbates diseases caused by coinfecting bacteria during coinfections.

Toll-like receptor 9 and 4 gene polymorphisms in susceptibility and severity of malaria: a meta-analysis of genetic association studies

BACKGROUND

Malaria is still a major public health problem in sub-Saharan Africa and South-east Asia. The clinical presentations of malaria infection vary from a mild febrile illness to life-threatening severe malaria. Toll like receptors (TLRs) are postulated to be involved in the innate immune responses to malaria. Individual studies showed inconclusive findings. This study aimed to assess the role of TLR4 (D299G, T399I) and TLR9 (T1237C, T1486C) in severity or susceptibility of malaria by meta-analysis of data from eligible studies.

METHODS

Relevant case-control studies that assessed the association between TLR 4/9 and malaria either in susceptibility or progression were searched in health-related electronic databases. Quality of included studies was evaluated with Newcastle-Ottawa scale. Pooled analyses for specific genetic polymorphisms were done under five genetic models. Stratified analysis was done by age and geographical region (Asian countries vs non-Asian countries).

RESULTS

Eleven studies (2716 cases and 2376 controls) from nine endemic countries were identified. Five studies (45.4%) obtained high score in quality assessment. Overall, a significant association between TLR9 (T1486C) and severity of malaria is observed in allele model (OR: 1.26, 95% CI: 1.08-1.48, I² = 0%) or homozygous model (OR: 1.55, 95% CI: 1.08-2.28, I² = 0%). For TLR9 (T1237C), a significant association with severity of malaria is observed in in heterozygous model (OR:1.89, 95% CI: 1.11-3.22, I² = 75%). On stratifications, TLR9 (T1486C) is only significantly associated with a subgroup of children of non-Asian countries under allele model (OR: 1.25, 95% CI: 1.02-1.38), while 1237 is with a subgroup of adults from Asian countries under heterozygous model (OR: 2.0, 95% CI: 1.09-3.64, I² = 39%). Regarding the susceptibility to malaria, TLR9 (T1237C) is significantly associated only with the children group under recessive model (OR: 2.21, 95% CI: 1.06-4.57, I²⁼85%) and homozygous model (OR: 1.49, 95% CI: 1.09-2.0, I² = 0%). For TLR4 (D299G, T399I), none is significantly associated with either severity of malaria or susceptibility to malaria under any genetic models.

CONCLUSIONS

The findings suggest that TLR 9 (T1486C and T1237C) seems to influence the progression of malaria, under certain genetic models and in specific age group of people from specific geographical region. TLR 9 (T1237C) also plays a role in susceptibility to malaria under certain genetic models and only with children of non-Asian countries. To substantiate these, future well designed studies with larger samples across endemic countries are needed.

Vaccines and the regulatory arm of the immune system. An overview from the Trypanosoma cruzi infection model

The knowledge that the immune system is composed of a regulatory/suppressor arm added a new point of view to better understand the nature of several pathologies including cancer, transplants, infections and autoimmune diseases. The striking discoveries concerning molecules and cells involved in this kind of regulation were followed by the elucidation of equally notable mechanisms used by several pathogens to manipulate the host immune system. Vaccines against pathogens are an invaluable tool developed to help the immune system cope with a potential infection or prevent disease pathology. Nowadays, there is accumulated evidence indicating that the powerful stimulation capacity of vaccines influences not only the effector arm of the immune system but also cells with regulatory/suppressor capacity, such as myeloid derived suppressor cells (MDSCs) and Foxp3+ regulatory T cells (Tregs). Trypanosoma cruzi (T. cruzi) is a protozoan parasite with a complex life cycle that has evolved several strategies to influence the regulatory immune response. Although diverse vaccine formulations have been able to stimulate the effector response, achieving non-sterilizing protection against T. cruzi, the influence of the vaccine candidates on the regulatory machinery has scarcely been assessed. This fact may not only reveal important information concerning how vaccines may influence cells with regulatory/suppressor capacity but also open the possibility to analyze whether vaccines are able to disrupt the mechanisms used by some pathogens to manipulate the host regulatory circuits. The aim of this review is to summarize and discuss available data related to the role of cellular components, like MDSCs and Foxp3+ Tregs, during T. cruzi infection, and the potential utility of those populations as additional targets for the rational design of vaccines.

Aberrant PD-1 ligand expression contributes to the myocardial inflammatory injury caused by Coxsackievirus B infection

Coxsackievirus group B (CVB) is considered as one of the most common pathogens of human viral myocarditis. CVB-induced myocarditis is mainly characterized by the persistence of the virus infection and immune-mediated inflammatory injury. Costimulatory signals are crucial for the activation of adaptive immunity. Our data reveal that the CVB type 3 (CVB3) infection altered the expression profile of costimulatory molecules in host cells. CVB3 infection caused the decrease of PD-1 ligand expression, partially due to the cleavage of AU-rich element binding protein AUF1 by the viral protease 3C^pro, leading to the exacerbated inflammatory injury of the myocardium. Moreover, systemic PD-L1 treatment, which augmented the apoptosis of proliferating lymphocytes, alleviated myocardial inflammatory injury. Our findings suggest that PD1-pathway can be a potential immunologic therapeutic target for CVB-induced myocarditis.

Characterization of T cell activation and regulation in children with asymptomatic Plasmodium falciparum infection

Background

Asymptomatic Plasmodium infections are characterized by the absence of clinical disease and the ability to restrict parasite replication. Increasing levels of regulatory T cells (Tregs) in Plasmodium falciparum infections have been associated with the risk of developing clinical disease, suggesting that individuals with asymptomatic infections may have reduced Treg frequency. However, the relationship between Tregs, cellular activation and parasite control in asymptomatic malaria remains unclear.

Methods

In a cross-sectional study, the levels of Tregs and other T cell activation phenotypes were compared using flow cytometry in symptomatic, asymptomatic and uninfected children before and after stimulation with infected red blood cell lysates (iRBCs). In addition, the association between these T cell phenotypes and parasitaemia were investigated.

Results

In children with asymptomatic infections, levels of Tregs and activated T cells were comparable to those in healthy controls but significantly lower than those in symptomatic children. After iRBC stimulation, levels of Tregs remained lower for asymptomatic versus symptomatic children. In contrast, levels of activated T cells were higher for asymptomatic children. Strikingly, the pre-stimulation levels of two T cell activation phenotypes (CD8+CD69+ and CD8+CD25+CD69+) and the post-stimulation levels of two regulatory phenotypes (CD4+CD25+Foxp3+ and CD8+CD25+Foxp3+) were significantly positively correlated with and explained 68% of the individual variation in parasitaemia. A machine-learning model based on levels of these four phenotypes accurately distinguished between asymptomatic and symptomatic children (sensitivity = 86%, specificity = 94%), suggesting that these phenotypes govern the observed variation in disease status.

Conclusion

Compared to symptomatic P. falciparum infections, in children asymptomatic infections are characterized by lower levels of Tregs and activated T cells, which are associated with lower parasitaemia. The results indicate that T cell regulatory and activation phenotypes govern both parasitaemia and disease status in paediatric malaria in the studied sub-Saharan African population.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2410-6) contains supplementary material, which is available to authorized users.

Mechanism of pattern recognition receptors (PRRs) and host pathogen interplay in bovine mastitis

Bacterial infection in the mammary gland parenchyma induces local and subsequently systemic inflammation that results in a complex disease. Mastitis in bovine is the result of various factors which function together. This review is aimed to analyze the factors involved in the pathogenesis of common bacterial species for bovine mastitis. The bacterial growth patterns, signaling pathway and the pathogen-associated molecular patterns (PAMPs) which activate immune responses is discussed. Clear differences in bacterial infection pattern are shown between bacterial species and illustrated TLRs, NLRs and RLGs molecular mechanism for the initiation of intramammary infection. The underlying reasons for the differences and the resulting host response are analyzed. Understandings of the mechanisms that activate and regulate these responses are central to the development of efficient anticipatory and treatment management. The knowledge of bovine mammary gland to common mastitis causing pathogens with possible immune mechanism could be a new conceptual understanding for the prospect of mastitis control program.

Association of TLR variants with susceptibility to Plasmodium vivax malaria and parasitemia in the Amazon region of Brazil

BACKGROUND

Plasmodium vivax malaria (Pv-malaria) is still considered a neglected disease despite an alarming number of individuals being infected annually. Malaria pathogenesis occurs with the onset of the vector-parasite-host interaction through the binding of pathogen-associated molecular patterns (PAMPs) and receptors of innate immunity, such as toll-like receptors (TLRs). The triggering of the signaling cascade produces an elevated inflammatory response. Genetic polymorphisms in TLRs are involved in susceptibility or resistance to infection, and the identification of genes involved with Pv-malaria response is important to elucidate the pathogenesis of the disease and may contribute to the formulation of control and elimination tools.

METHODOLOGY/PRINCIPAL FINDINGS

A retrospective case-control study was conducted in an intense transmission area of Pv-malaria in the state of Amazonas, Brazil. Genetic polymorphisms (SNPs) in different TLRs, TIRAP, and CD14 were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis in 325 patients infected with P. vivax and 274 healthy individuals without malaria history in the prior 12 months from the same endemic area. Parasite load was determined by qPCR. Simple and multiple logistic/linear regressions were performed to investigate association between the polymorphisms and the occurrence of Pv-malaria and parasitemia. The C/T (TLR5 R392StopCodon) and T/T (TLR9 -1486C/T) genotypes appear to be risk factors for infection by P. vivax (TLR5: C/C vs. C/T [OR: 2.116, 95% CI: 1.054-4.452, p = 0.031]; TLR9: C/C vs. T/T [OR: 1.919, 95% CI: 1.159-3.177, p = 0.010]; respectively). Fever (COEF = 7599.46, 95% CI = 3063.80-12135.12, p = 0.001) and the C/C genotype of TLR9 -1237C/T (COEF = 17006.63, 95% CI = 3472.83-30540.44, p = 0.014) were independently associated with increased parasitemia in patients with Pv-malaria.

CONCLUSIONS

Variants of TLRs may predispose individuals to infection by P. vivax. The TLR5 R392StopCodon and TLR9 -1486C/T variants are associated with susceptibility to Pv-malaria. Furthermore, the TLR9 variant -1237C/C correlates with high parasitemia.

Signaling Strategies of Malaria Parasite for Its Survival, Proliferation, and Infection during Erythrocytic Stage

Irrespective of various efforts, malaria persist the most debilitating effect in terms of morbidity and mortality. Moreover, the existing drugs are also vulnerable to the emergence of drug resistance. To explore the potential targets for designing the most effective antimalarial therapies, it is required to focus on the facts of biochemical mechanism underlying the process of parasite survival and disease pathogenesis. This review is intended to bring out the existing knowledge about the functions and components of the major signaling pathways such as kinase signaling, calcium signaling, and cyclic nucleotide-based signaling, serving the various aspects of the parasitic asexual stage and highlighted the Toll-like receptors, glycosylphosphatidylinositol-mediated signaling, and molecular events in cytoadhesion, which elicit the host immune response. This discussion will facilitate a look over essential components for parasite survival and disease progression to be implemented in discovery of novel antimalarial drugs and vaccines.

Malaria Parasites: The Great Escape

Parasites of the genus Plasmodium have a complex life cycle. They alternate between their final mosquito host and their intermediate hosts. The parasite can be either extra- or intracellular, depending on the stage of development. By modifying their shape, motility, and metabolic requirements, the parasite adapts to the different environments in their different hosts. The parasite has evolved to escape the multiple immune mechanisms in the host that try to block parasite development at the different stages of their development. In this article, we describe the mechanisms reported thus far that allow the Plasmodium parasite to evade innate and adaptive immune responses.

TLR4 and TLR9 signals stimulate protective immunity against blood-stage Plasmodium yoelii infection in mice

The mechanisms regulating the induction of protective immunity against blood-stage malaria remain unclear. Resistant DBA/2 mouse develops a higher Th1 response compared with a susceptible BALB/c strain during Plasmodium yoelii (Py) infection. It is known that the T helper cell response is initiated and polarized by dendritic cells (DCs) of the innate immune system, during which TLR4 and TLR9 are important receptors for the innate recognition of the malaria parasite and its products. We hypothesized that TLR4/9 may play critical roles in the induction of protective immunity against Py infection. We used TLR4/9 antagonists and agonists to study their effects on mouse resistance to Py infection. We found that the administration of an antagonist prior to infection aggravated disease outcomes, impaired DC functions and suppressed the pro-inflammatory response to Py infection in resistant DBA/2 mice. Treatment with the TLR4 agonist lipopolysaccharide (LPS) but not TLR9 agonist significantly improved the survival rate of susceptible Py-infected BALB/c mice. LPS administration promoted the activation and expansion of DCs and drove a Th1-biased response. Our data demonstrate the important roles of TLR4/9 signals in inducing resistance to malaria parasites and provide evidence for the rational use of TLR agonists to potentiate protective immunity against Plasmodium infection.

The role of regulatory T cells during Plasmodium chabaudi chabaudi AS infection in BALB/c mice

An inappropriate immune response to parasite infection is one of the primary drivers of malaria pathogenesis. Regulatory T cells (Tregs), an important subset of CD4(+) T cells, can maintain self-tolerance and prevent autoimmune diseases. However, there is little consensus about their role in malaria pathogenesis. In this study, we transiently depleted Tregs (CD25(+) T cells) using an anti-CD25 mAb (7D4 clone) at different time points following Plasmodium chabaudi chabaudi AS infection in BALB/c mice and investigated the effect of depletion of Tregs in this model. In control mice, Tregs proliferated significantly and their suppressive function was enhanced after infection. IL-10 was increased drastically during infection. Depletion of Tregs at various time points can lead to divergent outcomes. When Tregs were depleted prior to or during the early phase of infection, most mice survived and had a robust Th1 immune response. In contrast, when Tregs were depleted close to peak parasitemia, all mice died as a result of inflammation. Taken together, these data suggest that in P. c. chabaudi AS-infected BALB/c mice, Tregs inhibit the Th1 response and macrophage activation, leading to increased parasite load; however, they also control inflammation-mediated pathology by secreting high levels of IL-10.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

Immune Escape Mechanisms are Plasmodium's Secret Weapons Foiling the Success of Potent and Persistently Efficacious Malaria Vaccines

Despite decades of active research, an efficacious vaccine mediating long-term protection is still not available. This review highlights various mechanisms and the different facets by which the parasites outsmart the immune system. An understanding of how the parasites escape immune recognition and interfere with the induction of a protective immune response that provides sterilizing immunity will be crucial to vaccine design.

Toll-Like Receptor Gene Expression during Trichinella spiralis Infection

In Trichinella spiralis infection, type 2 helper T (Th2) cell-related and regulatory T (Treg) cell-related immune responses are the most important immune events. In order to clarify which Toll-like receptors (TLRs) are closely associated with these responses, we analyzed the expression of mouse TLR genes in the small intestine and muscle tissue during T. spiralis infection. In addition, the expression of several chemokine- and cytokine-encoding genes, which are related to Th2 and Treg cell mediated immune responses, were analyzed in mouse embryonic fibroblasts (MEFs) isolated from myeloid differentiation factor 88 (MyD88)/TIR-associated proteins (TIRAP) and Toll receptor-associated activator of interferons (TRIF) adapter protein deficient and wild type (WT) mice. The results showed significantly increased TLR4 and TLR9 gene expression in the small intestine after 2 weeks of T. spiralis infection. In the muscle, TLR1, TLR2, TLR5, and TLR9 gene expression significantly increased after 4 weeks of infection. Only the expression of the TLR4 and TLR9 genes was significantly elevated in WT MEF cells after treatment with excretory-secretory (ES) proteins. Gene expression for Th2 chemokine genes were highly enhanced by ES proteins in WT MEF cells, while this elevation was slightly reduced in MyD88/TIRAP(-/-) MEF cells, and quite substantially decreased in TRIF(-/-) MEF cells. In contrast, IL-10 and TGF-β expression levels were not elevated in MyD88/TIRAP(-/-) MEF cells. In conclusion, we suggest that TLR4 and TLR9 might be closely linked to Th2 cell and Treg cell mediated immune responses, although additional data are needed to convincingly prove this observation.

Regulatory T-Cells at the Interface between Human Host and Pathogens in Infectious Diseases and Vaccination

Regulatory T-cells (Tregs) act at the interface of host and pathogen interactions in human infectious diseases. Tregs are induced by a wide range of pathogens, but distinct effects of Tregs have been demonstrated for different pathogens and in different stages of infection. Moreover, Tregs that are induced by a specific pathogen may non-specifically suppress immunity against other microbes and parasites. Thus, Treg effects need to be assessed not only in homologous but also in heterologous infections and vaccinations. Though Tregs protect the human host against excessive inflammation, they probably also increase the risk of pathogen persistence and chronic disease, and the possibility of disease reactivation later in life. Mycobacterium leprae and Mycobacterium tuberculosis, causing leprosy and tuberculosis, respectively, are among the most ancient microbes known to mankind, and are master manipulators of the immune system toward tolerance and pathogen persistence. The majority of mycobacterial infections occur in settings co-endemic for viral, parasitic, and (other) bacterial coinfections. In this paper, we discuss recent insights in the activation and activity of Tregs in human infectious diseases, with emphasis on early, late, and non-specific effects in disease, coinfections, and vaccination. We highlight mycobacterial infections as important models of modulation of host responses and vaccine-induced immunity by Tregs.

L-arginine exacerbates experimental cerebral malaria by enhancing pro-inflammatory responses

L-Arginine (L-Arg), the substrate for nitric oxide (NO) synthase, has been used to treat malaria to reverse endothelial dysfunction in adults. However, the safety and efficacy of L-Arg remains unknown in malaria patients under the age of five, who are at the greatest risk of developing cerebral malaria (CM), a severe malaria complication. Here, we tested effects of L-Arg treatment on the outcomes of CM using a mouse model. Experimental cerebral malaria (ECM) was induced in female C57BL/6 mice infected with Plasmodium berghei ANKA, and L-Arg was administrated either prophylactically or after parasite infection. Surprisingly, both types of L-Arg administration caused a decline in survival time and raised CM clinical scores. L-Arg treatment increased the population of CD4(+)T-bet(+)IFN-γ(+) Th1 cells and the activated macrophages (F4/80(+)CD36(+)) in the spleen. The levels of pro-inflammatory cytokines, IFN-γ and TNF-α, in splenocyte cultures were also increased by L-Arg treatment. The above changes were accompanied with a rise in the number of dendritic cells (DCs) and an increase in their maturation. However, L-Arg did not affect the population of regulatory T cells or the level of IL-10 in the spleen. Taken together, these data suggest that L-Arg may enhance the Th1 immune response, which is essential for a protective response in uncomplicated malaria but could be lethal in CM patients. Therefore, the prophylactic use of L-Arg to treat CM, based on the assumption that restoring the bioavailability of endothelial NO improves the outcome of CM, may need to be reconsidered especially for children.

Plasmodium berghei infection ameliorates atopic dermatitis-like skin lesions in NC/Nga mice

Background

Atopic diseases are more prevalent in industrialized countries than in developing countries. In addition, significant differences in the prevalence of allergic diseases are observed between rural and urban areas within the same country. This difference in prevalence has been attributed to what is called the ‘hygiene hypothesis’. Although parasitic infections are known to protect against allergic reactions, the mechanism is still unknown. The aim of this study was to investigate whether or not malarial infections can inhibit atopic dermatitis (AD)-like skin lesions in a mouse model of AD.

Methods

We used NC/Nga mice which are a model for AD. The NC/Nga mice were intraperitoneally infected with 1 × 10⁵Plasmoduim berghei (Pb) XAT-infected erythrocytes.

Results

Malarial infections ameliorated AD-like skin lesions in the NC/Nga mice. This improvement was blocked by the administration of anti-asialo GM1 antibodies, which are anti-natural killer (NK) cells. Additionally, adoptive transfer of NK cells markedly improved AD-like skin lesions in conventional NC/Nga mice; these suggest that the novel protective mechanism associated with malaria parasitic infections is at least, in part, dependent on NK cells.

Conclusions

We have experimentally demonstrated for the first time that malarial infections ameliorated AD-like skin lesions in a mouse model of AD. Our study could explain in part the mechanism of the ‘hygiene hypothesis’, which states that parasitic infections can inhibit the development of allergic diseases.

Plasmodium falciparum induces Foxp3hi CD4 T cells independent of surface PfEMP1 expression via small soluble parasite components

Elevated levels of regulatory T cells following Plasmodium infection are a well-reported phenomenon that can influence both protective and pathological anti-parasite responses, and might additionally impact on vaccine responses in acutely malaria infected individuals. The mechanisms underlying their induction or expansion by the parasite, however, are incompletely understood. In a previous study, Plasmodium falciparum infected red blood cells (iRBCs) were shown to induce effector-cytokine producing Foxp3int CD4+ T cells, as well as regulatory Foxp3hi CD4+ T cells in vitro. The aim of the present study was to determine the contribution of parasite components to the induction of Foxp3 expression in human CD4+ T cells. Using the surface PfEMP1-deficient parasite line 1G8, we demonstrate that induction of Foxp3hi and Foxp3int CD4+ T cells is independent of PfEMP1 expression on iRBCs. We further demonstrate that integrity of iRBCs is no requirement for the induction of Foxp3 expression. Finally, transwell experiments showed that induction of Foxp3 expression, and specifically the generation of Foxp3hi as opposed to Foxp3int CD4 T cells, can be mediated by soluble parasite components smaller than 20 nm and thus likely distinct from the malaria pigment hemozoin. These results suggest that the induction of Foxp3hi T cells by P. falciparum is largely independent of two key immune modulatory parasite components, and warrant future studies into the nature of the Foxp3hi inducing parasite components to potentially allow their exclusion from vaccine formulations.

Relationship of regulatory T cells to Plasmodium falciparum malaria symptomatology in a hypoendemic region

BACKGROUND

Previous data have suggested that regulatory T cells (Tregs) balance protective immune responses with immune mediated pathology in malaria. This study aimed to determine to test the hypothesis that Treg proportions or absolute levels are associated with parasitaemia and malaria symptoms.

METHODS

Treg cells were quantified by flow cytometry as CD4+ CD25+, Foxp3+, CD127(low) T cells. Three patient groups were assessed: patients with symptomatic Plasmodium falciparum malaria (S), subjects with asymptomatic P. falciparum parasitaemia (AS) and uninfected control individuals (C).

RESULTS

S, AS and C groups had similar absolute numbers and percentage of Tregs (3.9%, 3.5% and 3.5% respectively). Levels of parasitaemia were not associated with Treg percentage (p = 0.47).

CONCLUSION

Neither relative nor absolute regulatory T cell numbers were found to be associated with malaria-related symptomatology in this study. Immune mechanisms other than Tregs are likely to be responsible for the state of asymptomatic P. falciparum parasitaemia in the Peruvian Amazon; but further study to explore these mechanisms is needed.

Association of cytokine and Toll-like receptor gene polymorphisms with severe malaria in three regions of Cameroon

P. falciparum malaria is one of the most widespread and deadliest infectious diseases in children under five years in endemic areas. The disease has been a strong force for evolutionary selection in the human genome, and uncovering the critical human genetic factors that confer resistance to the disease would provide clues to the molecular basis of protective immunity that would be invaluable for vaccine development. We investigated the effect of single nucleotide polymorphisms (SNPs) on malaria pathology in a case- control study of 1862 individuals from two major ethnic groups in three regions with intense perennial P. falciparum transmission in Cameroon. Twenty nine polymorphisms in cytokine and toll-like receptor (TLR) genes as well as the sickle cell trait (HbS) were assayed on the Sequenom iPLEX platform. Our results confirm the known protective effect of HbS against severe malaria and also reveal a protective effect of SNPs in interleukin-10 (IL10) cerebral malaria and hyperpyrexia. Furthermore, IL17RE rs708567 GA and hHbS rs334 AT individuals were associated with protection from uncomplicated malaria and anaemia respectively in this study. Meanwhile, individuals with the hHbS rs334 TT, IL10 rs3024500 AA, and IL17RD rs6780995 GA genotypes were more susceptible to severe malarial anaemia, cerebral malaria, and hyperpyrexia respectively. Taken together, our results suggest that polymorphisms in some immune response genes may have important implications for the susceptibility to severe malaria in Cameroonians. Moreover using uncomplicated malaria may allow us to identify novel pathways in the early development of the disease.

HLA class II (DR0401) molecules induce Foxp3+ regulatory T cell suppression of B cells in Plasmodium yoelii strain 17XNL malaria

Unlike human malaria parasites that induce persistent infection, some rodent malaria parasites, like Plasmodium yoelii strain 17XNL (Py17XNL), induce a transient (self-curing) malaria infection. Cooperation between CD4 T cells and B cells to produce antibodies is thought to be critical for clearance of Py17XNL parasites from the blood, with major histocompatibility complex (MHC) class II molecules being required for activation of CD4 T cells. In order to better understand the correspondence between murine malaria models and human malaria, and in particular the role of MHC (HLA) class II molecules, we studied the ability of humanized mice expressing human HLA class II molecules to clear Py17XNL infection. We showed that humanized mice expressing HLA-DR4 (DR0401) molecules and lacking mouse MHC class II molecules (EA(0)) have impaired production of specific antibodies to Py17XNL and cannot cure the infection. In contrast, mice expressing HLA-DR4 (DR0402), HLA-DQ6 (DQ0601), HLA-DQ8 (DQ0302), or HLA-DR3 (DR0301) molecules in an EA(0) background were able to elicit specific antibodies and self-cure the infection. In a series of experiments, we determined that the inability of humanized DR0401.EA(0) mice to elicit specific antibodies was due to expansion and activation of regulatory CD4(+) Foxp3(+) T cells (Tregs) that suppressed B cells to secrete antibodies through cell-cell interactions. Treg depletion allowed the DR0401.EA(0) mice to elicit specific antibodies and self-cure the infection. Our results demonstrated a differential role of MHC (HLA) class II molecules in supporting antibody responses to Py17XNL malaria and revealed a new mechanism by which malaria parasites stimulate B cell-suppressogenic Tregs that prevent clearance of infection.

Pre-existing Schistosoma japonicum infection alters the immune response to Plasmodium berghei infection in C57BL/6 mice

BACKGROUND

Since helminths and malaria parasites are often co-endemic, it is important to clarify the immunoregulatory mechanism that occurs during the process of co-infection. A previous study confirmed that dendritic cells (DCs) are involved in the establishment and regulation of the T-cell-mediated immune response to malaria infection. In the current study, distinct response profiles for splenic DCs and regulatory T cell (Treg) responses were assessed to evaluate the effects of a pre-existing Schistosoma japonicum infection on malaria infection.

METHODS

Malaria parasitaemia, survival rate, brain histopathology and clinical experimental cerebral malaria (ECM) were assessed in both Plasmodium berghei ANKA-mono-infected and S. japonicum-P. berghei ANKA-co-infected mice. Cell surface/intracellular staining and flow cytometry were used to analyse the level of splenic DC subpopulations, toll-like receptors (TLRs), DC surface molecules, Tregs (CD4⁺CD25⁺Foxp3⁺), IFN-γ/IL-10-secreting Tregs, and IFN-γ⁺/IL-10⁺-Foxp3⁻CD4⁺ T cells. IFN-γ, IL-4, IL-5, IL-10 and IL-13 levels were determined in splenocyte supernatants using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The co-infected mice had significantly higher malaria parasitaemia, compared with the mono-infected mice, on days 2, 3, 7 and 8 after P. berghei ANKA infection. Mono-infected mice had a slightly lower survival rate, while clinical ECM symptoms, and brain pathology, were significantly more severe during the period of susceptibility to ECM. On days 5 and 8 post P. berghei ANKA infection, co-infected mice had significantly lower levels of CD11c⁺CD11b⁺, CD11c⁺CD45R/B220⁺, CD11c⁺TLR4⁺, CD11c⁺TLR9⁺, CD11c⁺MHCII⁺, CD11c⁺CD86⁺, IFN-γ-secreting Tregs, and IFN-γ⁺Foxp3⁻CD4⁺ T cells in single-cell suspensions of splenocytes when compared with P. berghei ANKA-mono-infected mice. Co-infected mice also had significantly lower levels of IFN-γ and higher levels of IL-4, IL-5, and IL-13 in splenocyte supernatants compared to mono-infected mice. There were no differences in the levels of IL-10-secreting Tregs or IL-10⁺Foxp3⁻CD4⁺ T cells between co-infected and mono-infected mice.

CONCLUSIONS

A Tregs-associated Th2 response plays an important role in protecting against ECM pathology. Pre-existing S. japonicum infection suppressed TLR ligand-induced DC maturation and had an anti-inflammatory effect during malaria infection not only by virtue of its ability to induce Th2 responses, but also by directly suppressing the ability of DC to produce pro-inflammatory mediators.

IL-23 protection against Plasmodium berghei infection in mice is partially dependent on IL-17 from macrophages

Although IL-12 is believed to contribute to protective immune responses, the role played by IL-23 (a member of the IL-12 family) in malaria is elusive. Here, we show that IL-23 is produced during infection with Plasmodium berghei NK65. Mice deficient in IL-23 (p19KO) had higher parasitemia and died earlier than wild-type (WT) controls. Interestingly, p19KO mice had lower numbers of IL-17-producing splenic cells than their WT counterparts. Furthermore, mice deficient in IL-17 (17KO) suffered higher parasitemia than the WT controls, indicating that IL-23-mediated protection is dependent on induction of IL-17 during infection. We found that macrophages were responsible for IL-17 production in response to IL-23. We observed a striking reduction in splenic macrophages in the p19KO and 17KO mice, both of which became highly susceptible to infection. Thus, IL-17 appears to be crucial for maintenance of splenic macrophages. Adoptive transfer of macrophages into macrophage-depleted mice confirmed that macrophage-derived IL-17 is required for macrophage accumulation and parasite eradication in the recipient mice. We also found that IL-17 induces CCL2/7, which recruit macrophages. Our findings reveal a novel protective mechanism whereby IL-23, IL-17, and macrophages reduce the severity of infection with blood-stage malaria parasites.

Foxp3+ regulatory T cells are required for recovery from severe sepsis

The role of regulatory T cells (Tregs) in bacterial sepsis remains controversial because antibody-mediated depletion experiments gave conflicting results. We employed DEREG mice (DEpletion of REGulatory T cells) and a caecal ligation and puncture model to elucidate the role of CD4⁺Foxp3⁺ Tregs in sepsis. In DEREG mice natural Tregs can be visualized easily and selectively depleted by diphtheria toxin because the animals express the diphtheria toxin receptor and enhanced green fluorescent protein as a fusion protein under the control of the foxp3 locus. We confirmed rapid Treg-activation and an increased ratio of Tregs to Teffs in sepsis. Nevertheless, 24 h after sepsis induction, Treg-depleted and control mice showed equally strong inflammation, immune cell immigration into the peritoneum and bacterial dissemination. During the first 36 h of disease survival was not influenced by Treg-depletion. Later, however, only Treg-competent animals recovered from the insult. We conclude that the suppressive capacity of Tregs is not sufficient to control overwhelming inflammation and early mortality, but is a prerequisite for the recovery from severe sepsis.

Co-activation through TLR4 and TLR9 but not TLR2 skews Treg-mediated modulation of Igs and induces IL-17 secretion in Treg: B cell co-cultures

Whereas Th17 cells are associated with aggravated inflammation, regulatory T cells (Tregs) provide an environment to control overt responses. Nevertheless, Tregs display a certain degree of plasticity demonstrating that T cell differentiation processes are not absolute. Previously, we showed that human Treg clones induced B cells to produce IgG4. Here we focus on the actions of freshly isolated CD4(+)CD25(+)Foxp3(+)CD127(dim) Tregs on Ig production by B cells and the consequences of prior TLR activation of B cells. In the absence of TLR stimuli, Tregs, but not conventional T cells, dampened B cell proliferation, plasma cell formation and, with the exception of IgG4, all other Ig production. Although IgG4 levels were unchanged in total B cell:Treg co-cultures, levels were increased in Treg co-cultures of naive, but not memory, B cells. Triggering TLR on B cells skewed both Ig and cytokine secretion patterns and, surprisingly, Tregs within TLR4- and TLR9- but not TLR2-triggered B cell co-cultures up-regulated retinoic acid related orphan receptor (RORC) and produced IL-17. These data indicate that under conditions like bacterial or viral infections, B cells can escape Treg control, and provides an explanation as to why patients suffering from allergy or helminth infections display polar immunopathological symptoms despite being exposed to the same agent.

Supplement of L-Arg improves protective immunity during early-stage Plasmodium yoelii 17XL infection

L-arginine (L-Arg), the precursor of nitric oxide (NO), plays multiple important roles in nutrient metabolism and immune regulation. L-Arg supplement serves as a potential adjunctive therapy for severe malaria, because it improves NO bioavailability and reverses endothelial dysfunction in severe malaria patients. In this study, we investigated the effect of dietary L-Arg supplement on host immune responses during subsequent malaria infection using the Plasmodium yoelii 17XL - BALB/c mouse model. We have shown that pretreatment of mice with L-Arg significantly decreased parasitemia and prolonged the survival time of mice after infection. L-Arg supplement led to significant increases in activated CD4(+)T-bet(+)IFN-γ(+) T cells and F4/80(+)CD36(+) macrophages during early-stage infection, which were accompanied by enhanced synthesis of IFN-γ, TNF-α and NO by spleen cells. Moreover, L-Arg-pretreated mice developed more splenic myeloid and plasmacytoid dendritic cells with up-regulated expression of MHC II, CD86 and TLR9. In comparison, L-Arg treatment did not change the number of regulatory T cells and the level of anti-inflammatory cytokine IL-10. Taken together, our results showed that L-Arg pretreatment could improve the protective immune response in experimental malaria infection in mice, which underlines potential importance of L-Arg supplement in malaria-endemic human populations.

Freeze-thaw lysates of Plasmodium falciparum-infected red blood cells induce differentiation of functionally competent regulatory T cells from memory T cells

In addition to naturally occurring regulatory T (nTreg) cells derived from the thymus, functionally competent Treg cells can be induced in vitro from peripheral blood lymphocytes in response to TCR stimulation with cytokine costimulation. Using these artificial stimulation conditions, both naïve as well as memory CD4⁺ T cells can be converted into induced Treg (iTreg) cells, but the cellular origin of such iTreg cells in vivo or in response to more physiologic stimulation with pathogen-derived antigens is less clear. Here, we demonstrate that a freeze/thaw lysate of Plasmodium falciparum schizont extract (PfSE) can induce functionally competent Treg cells from peripheral lymphocytes in a time- and dose-dependent manner without the addition of exogenous costimulatory factors. The PfSE-mediated induction of Treg cells required the presence of nTreg cells in the starting culture. Further experiments mixing either memory or naïve T cells with antigen presenting cells and CFSE-labeled Treg cells identified CD4⁺CD45RO⁺CD25⁻ memory T cells rather than Treg cells as the primary source of PfSE-induced Treg cells. Taken together, these data suggest that in the presence of nTreg cells, PfSE induces memory T cells to convert into iTreg cells that subsequently expand alongside PfSE-induced effector T cells.

TLR7 and TLR9 in SLE: when sensing self goes wrong

Autoreactive B and T cells are present in healthy, autoimmunity-free individuals, but they are kept in check by various regulatory mechanisms. In systemic lupus erythematosus (SLE) patients, however, autoreactive cells are expanded, activated, and produce large quantities of autoantibodies, directed especially against nuclear antigens. These antibodies form immune complexes with self-nucleic acids present in SLE serum. Since self-DNA and self-RNA in the form of protein complexes can act as TLR9 and TLR7 ligands, respectively, TLR stimulation is suggested as an additional signal contributing to activation and/or modulation of the aberrant adaptive immune response. Data from mouse models suggest a pathogenic role for TLR7 and a protective role for TLR9 in the pathogenesis of SLE. Future investigations are needed to elucidate the underlying modulatory mechanisms and the role of TLR7 and TLR9 in the complex pathogenesis of human SLE.

Allicin enhances host pro-inflammatory immune responses and protects against acute murine malaria infection

Background

During malaria infection, multiple pro-inflammatory mediators including IFN-γ, TNF and nitric oxide (NO) play a crucial role in the protection against the parasites. Modulation of host immunity is an important strategy to improve the outcome of malaria infection. Allicin is the major biologically active component of garlic and shows anti-microbial activity. Allicin is also active against protozoan parasites including Plasmodium, which is thought to be mediated by inhibiting cysteine proteases. In this study, the immunomodulatory activities of allicin were assessed during acute malaria infection using a rodent malaria model Plasmodium yoelii 17XL.

Methods

To determine whether allicin modulates host immune responses against malaria infection, mice were treated with allicin after infection with P. yoelii 17XL. Mortality was checked daily and parasitaemia was determined every other day. Pro-inflammatory mediators and IL-4 were quantified by ELISA, while NO level was determined by the Griess method. The populations of dendritic cells (DCs), macrophages, CD4⁺ T and regulatory T cells (Treg) were assessed by FACS.

Results

Allicin reduced parasitaemia and prolonged survival of the host in a dose-dependent manner. This effect is at least partially due to improved host immune responses. Results showed that allicin treatment enhanced the production of pro-inflammatory mediators such as IFN-γ, TNF, IL-12p70 and NO. The absolute numbers of CD4⁺ T cells, DCs and macrophages were significantly higher in allicin-treated mice. In addition, allicin promoted the maturation of CD11c⁺ DCs, whereas it did not cause major changes in IL-4 and the level of anti-inflammatory cytokine IL-10.

Conclusions

Allicin could partially protect host against P. yoelii 17XL through enhancement of the host innate and adaptive immune responses.

Targeting Toll-like receptors by chloroquine protects mice from experimental cerebral malaria

Excessive production of proinflammatory cytokines, elicited mostly by Th1 cells, is an important cause of cerebral malaria (CM). Dendritic cells (DCs), a critical link between innate and adaptive immune responses, rely heavily on Toll-like receptor (TLR) signaling. Using C57BL/6 mice infected with Plasmodium berghei ANKA (PbA) as an experimental CM model, we first confirmed that inhibition of TLR9 by suppressive oligodeoxynucleotides protected mice from CM. In addition to being a well-known antimalarial, chloroquine (CQ) has been used as an immunomodulator of endocytic TLRs because it inhibits endosomal acidification. We found that immediately before and shortly after infection by PbA, treatment with a single dose of 50 mg/kg of CQ protected mice from experimental CM. Both CQ treatments significantly inhibited expression of TLR9 and MHC-II on DCs, and reduced the number of myeloid and plasmatocytoid DCs at 3 and 5 days after infection. Consequently, activation of CD4+ T cells, especially the expansion of the Th1 subsets, was dramatically inhibited in CQ treated groups, which was accompanied by a remarkable decline in the production of Th1 type proinflammatory mediators IFN-γ, TNF-α, and nitric oxide. Taken together, these results corroborated the involvement of TLR9 in CM pathogenesis and suggest that interference with the activation of this receptor is a promising strategy to prevent deleterious inflammatory response mediating pathogenesis and severity of malaria.

Polysaccharides from the Chinese medicinal herb Achyranthes bidentata enhance anti-malarial immunity during Plasmodium yoelii 17XL infection in mice

BACKGROUND

Clinical immunity to malaria in human populations is developed after repeated exposure to malaria. Regulation and balance of host immune responses may lead to optimal immunity against malaria parasite infection. Polysaccharides (ABPS) derived from the Chinese herb ox knee Achyranthes bidentata possess immuno-modulatory functions. The aim of this study is to use the rodent malaria model Plasmodium yoelii 17XL (P. y17XL) to examine whether pretreatment with ABPS will modulate host immunity against malaria infection and improve the outcome of the disease.

METHODS

To determine whether ABPS could modulate immunity against malaria, mice were pretreated with ABPS prior to blood-stage infection by P. y17XL. Host survival and parasitaemia were monitored daily. The effect of pretreatment on host immune responses was studied through the quantitation of cytokines, dendritic cell populations, and natural regulatory T cells (Treg).

RESULTS

Pretreatment with ABPS prior to infection significantly extended the survival time of mice after P. y17XL infection. At three and five days post-infection, ABPS pretreated mice developed stronger Th1 immune responses against malaria infection with the number of F4/80+CD36+ macrophages and levels of IFN-γ, TNF-α and nitric oxide being significantly higher than in the control group. More importantly, ABPS-treated mice developed more myeloid (CD11c+CD11b+) and plasmacytoid dendritic cells (CD11c+CD45R+/B220+) than control mice. ABPS pretreatment also resulted in modulated expression of MHC-II, CD86, and especially Toll-like receptor 9 by CD11c+ dendritic cells. In comparison, pretreatment with ABPS did not alter the number of natural Treg or the production of the anti-inflammatory cytokine IL-10.

CONCLUSION

Pretreatment with the immuno-modulatory ABPS selectively enhanced Th1 immune responses to control the proliferation of malaria parasites, and prolonged the survival of mice during subsequent malaria infection.

Haematological parameters, natural regulatory CD4 + CD25 + FOXP3+ T cells and γδ T cells among two sympatric ethnic groups having different susceptibility to malaria in Burkina Faso

BACKGROUND

Fulani ethnic group individuals are less susceptible than sympatric Mossi ethnic group, in term of malaria infection severity, and differ in antibody production against malaria antigens. The differences in susceptibility to malaria between Fulani and Mossi ethnic groups are thought to be regulated by different genetic backgrounds and offer the opportunity to compare haematological parameters, Tregs and γδT cell profiles in seasonal and stable malaria transmission settings in Burkina Faso. The study was conducted at two different time points i.e. during the high and low malaria transmission period.

RESULTS

Two cross-sectional surveys were undertaken in adults above 20 years belonging either to the Fulani or the Mossi ethnic groups 1) at the peak of the malaria transmission season and 2) during the middle of the low malaria transmission season. Full blood counts, proportions of Tregs and γδ T cells were measured at both time-points.As previously shown the Fulani and Mossi ethnic groups showed a consistent difference in P. falciparum infection rates and parasite load. Differential white blood cell counts showed that the absolute lymphocyte counts were higher in the Mossi than in the Fulani ethnic group at both time points. While the proportion of CD4+CD25high was higher in the Fulani ethnic group at the peak of malaria transmission season (p = 0.03), no clear pattern emerged for T regulatory cells expressing FoxP3+ and CD127low. However CD3+γδ+ subpopulations were found to be higher in the Fulani compared to the Mossi ethnic group, and this difference was statistically significant at both time-points (p = 0.004 at low transmission season and p = 0.04 at peak of transmission).

CONCLUSION

Our findings on regulatory T cell phenotypes suggest an interesting role for immune regulatory mechanisms in response to malaria. The study also suggests that TCRγδ + cells might contribute to the protection against malaria in the Fulani ethnic group involving their reported parasite inhibitory activities.

Analysis of CD83 antigen expression in human breast fibroadenoma and adjacent tissue

CONTEXT AND OBJECTIVE

Dendritic cell maturation is considered essential for starting an immune response. The CD83 antigen is an important marker of dendritic cell maturation. The objectives here were to analyze CD83 antigen expression in human breast fibroadenoma and breast tissue adjacent to the lesion and to identify clinical factors that might influence this expression.

DESIGN AND SETTING

This was a retrospective study at a public university hospital, in which 29 histopathological samples of breast fibroadenoma and adjacent breast tissue, from 28 women of reproductive age, were analyzed.

METHODS

The immunohistochemistry method was used to analyze the cell expression of the antigen. The antigen expression in the cells was evaluated by means of random manual counting using an optical microscope.

RESULTS

Positive expression of the CD83 antigen in the epithelial cells of the fibroadenoma (365.52; standard deviation ± 133.13) in relation to the adjacent breast tissue cells (189.59; standard deviation ± 140.75) was statistically larger (P < 0.001). Several clinical features were analyzed, but only parity was shown to influence CD83 antigen expression in the adjacent breast tissue, such that positive expression was more evident in nulliparous women (P = 0.042).

CONCLUSIONS

The expression of the CD83 antigen in the fibroadenoma was positive and greater than in the adjacent breast tissue. Positive expression of the antigen in the adjacent breast tissue was influenced by parity, and was significantly more evident in nulliparous women.

Role of interleukin-10 in malaria: focusing on coinfection with lethal and nonlethal murine malaria parasites

Interleukin- (IL-) 10, anti-inflammatory cytokine, is known to inhibit the protective immune responses against malaria parasites and to be involved in exacerbating parasitemia during Plasmodium infection. In contrast, IL-10 is regarded as necessary for suppressing severe pathology during Plasmodium infection. Here, we summarize the role of IL-10 during murine malaria infection, focusing especially on coinfection with lethal and nonlethal strains of malaria parasites. Recent studies have demonstrated that the major sources of IL-10 are subpopulations of CD4⁺ T cells in humans and mice infected with Plasmodium. We also discuss the influence of innate immunity on the induction of CD4⁺ T cells during murine malaria coinfection.

Insufficiently defined genetic background confounds phenotypes in transgenic studies as exemplified by malaria infection in Tlr9 knockout mice

The use of genetically modified mice, i.e. transgenic as well as gene knockout (KO) and knock-in mice, has become an established tool to study gene function in many animal models for human diseases . However, a gene functions in a particular genomic context. This implies the importance of a well-defined homogenous genetic background for the analysis and interpretation of phenotypes associated with genetic mutations. By studying a Plasmodium chabaudi chabaudi AS (PcAS) malaria infection in mice bearing a TLR9 null mutation, we found an increased susceptibility to infection, i.e. higher parasitemia levels and increased mortality. However, this was not triggered by the deficient TLR9 gene itself. Instead, this disease phenotype was dependent on the heterogeneous genetic background of the mice, which appeared insufficiently defined as determined by single nucleotide polymorphism (SNP) analysis. Hence, it is of critical importance to study gene KO phenotypes on a homogenous genetic background identical to that of their wild type (WT) control counterparts. In particular, to avoid problems related to an insufficiently defined genetic background, we advocate that for each study involving genetically modified mice, at least a detailed description of the origin and genetic background of both the WT control and the altered strain of mice is essential.

Mechanisms underlying the induction of regulatory T cells and its relevance in the adaptive immune response in parasitic infections

To fulfill its function, the immune system must detect and interpret a wide variety of signals and adjust the magnitude, duration, and specific traits of each response during the complex host-parasite relationships in parasitic infections. Inflammation must be tightly regulated since uncontrolled inflammation may be as destructive as the triggering stimulus and leads to immune-mediated tissue injury.

During recent years, increasing evidence points to regulatory T cells (Tregs) as key anti-inflammatory cells, critically involved in limiting the inflammatory response. Herein, we review the published information on the induction of Tregs and summarize the most recent findings on Treg generation in parasitic diseases.

Virus infection stages and distinct Th1 or Th17/Th22 T-cell responses in malaria/SHIV coinfection correlate with different outcomes of disease

BACKGROUND

Malaria and AIDS represent 2 leading causes of death from infectious diseases worldwide, and their high geographic overlap means coinfection is prevalent. It remains unknown whether distinct immune responses during coinfection with malaria and human immunodeficiency virus (HIV) affect clinical outcomes.

METHODS

We tested this hypothesis by employing macaque models of coinfection with malaria and simian-human immunodeficiency virus (SHIV).

RESULTS

Plasmodium fragile malaria coinfection of acutely SHIV-infected macaques induced hyperimmune activation and remarkable expansion of CD4+ and CD8+ T effector cells de novo producing interferon γ or tumor necrosis factor α. Malaria-driven cellular hyperactivation/expansion and high-level Th1-cytokines enhanced SHIV disease characterized by increasing CD4+ T-cell depletion, profound lymphoid depletion or destruction, and even necrosis in lymph nodes and spleens. Importantly, malaria/SHIV-mediated depletion, destruction, and necrosis in lymphoid tissues led to bursting parasite replication and fatal virus-associated malaria. Surprisingly, chronically SHIV-infected macaques without AIDS employed different defense mechanisms during malaria coinfection, and mounted unique ∼200-fold expansion of interleukin 17+/interleukin 22+ T effectors with profound Th1 suppression. Such remarkable expansion of Th17/Th22 cells and inhibition of Th1 response coincided with development of immunity against fatal virus-associated malaria without accelerating SHIV disease.

CONCLUSIONS

These novel findings suggest that virus infection status and selected Th1 or Th17/Th22 responses after malaria/AIDS-virus coinfection correlate with distinct outcomes of virus infection and malaria.

Foxp3+ regulatory T cells impede the priming of protective CD8+ T cells

T cell activation is controlled by incompletely defined opposing stimulation and suppression signals that together sustain the balance between optimal host defense against infection and peripheral tolerance. In this article, we explore the impacts of Foxp3(+) regulatory T cell (Treg) suppression in priming Ag-specific T cell activation under conditions of noninfection and infection. We find the transient ablation of Foxp3(+) Tregs unleashes the robust expansion and activation of peptide-stimulated CD8(+) T cells that provide protection against Listeria monocytogenes infection in an Ag-specific fashion. By contrast, Treg ablation had nonsignificant impacts on the CD8(+) T cell response primed by infection with recombinant L. monocytogenes. Similarly, nonrecombinant L. monocytogenes administered with peptide stimulated the expansion and activation of CD8(+) T cells that paralleled the response primed by Treg ablation. Interestingly, these adjuvant properties of L. monocytogenes did not require CD8(+) T cell stimulation by IL-12 produced in response to infection, but instead were associated with sharp reductions in Foxp3(+) Treg suppressive potency. Therefore, Foxp3(+) Tregs impose critical barriers that, when overcome naturally during infection or artificially with ablation, allow the priming of protective Ag-specific CD8(+) T cells.

Toll-like receptors and their crosstalk with other innate receptors in infection and immunity

Toll-like receptors (TLRs) are germline-encoded pattern recognition receptors (PRRs) that play a central role in host cell recognition and responses to microbial pathogens. TLR-mediated recognition of components derived from a wide range of pathogens and their role in the subsequent initiation of innate immune responses is widely accepted; however, the recent discovery of non-TLR PRRs, such as C-type lectin receptors, NOD-like receptors, and RIG-I-like receptors, suggests that many aspects of innate immunity are more sophisticated and complex. In this review, we will focus on the role played by TLRs in mounting protective immune responses against infection and their crosstalk with other PRRs with respect to pathogen recognition.

A critical role for phagocytosis in resistance to malaria in iron-deficient mice

Both iron-deficient anemia (IDA) and malaria remain a threat to children in developing countries. Children with IDA are resistant to malaria, but the reasons for this are unknown. In this study, we addressed the mechanisms underlying the protection against malaria observed in IDA individuals using a rodent malaria parasite, Plasmodium yoelii (Py). We showed that the intra-erythrocytic proliferation and amplification of Py parasites were not suppressed in IDA erythrocytes and immune responses specific for Py parasites were not enhanced in IDA mice. We also found that parasitized IDA cells were more susceptible to engulfment by phagocytes in vitro than control cells, resulting in rapid clearance of parasitized cells and that protection of IDA mice from malaria was abrogated by inhibiting phagocytosis. One possible reason for this rapid clearance might be increased exposure of phosphatidylserine at the outer leaflet of parasitized IDA erythrocytes. The results of this study suggest that parasitized IDA erythrocytes are eliminated by phagocytic cells, which sense alterations in the membrane structure of parasitized IDA erythrocytes.

Detecting mutations in PfCRT and PfMDR1 genes among Plasmodium falciparum isolates from Saudi Arabia by pyrosequencing

The emergence of chloroquine resistance in Plasmodium falciparum is a significant public health problem where malaria is endemic. We aimed to evaluate the efficacy of pyrosequencing to assess chloroquine resistance among P. falciparum isolates from the southwestern region of Saudi Arabia by analyzing the K76T and N86Y mutations in the P. falciparum chloroquine resistance transporter (PfCRT) and P. falciparum multidrug resistance 1 (PfMDR1) genes, respectively. Blood samples (n = 121) from microscopically positive P. falciparum cases were collected. DNA was extracted, and fragments from each of the genes were amplified by PCR using new sets of primers. The amplicons were sequenced using a pyrosequencer. All of the 121 samples were amplified for assessment of the PfCRT K76T and PfMDR1 N86Y mutations. All of the samples amplified for the PfCRT 76T mutation harbored the ACA codon (121/121; 100%), indicating the presence of the 76T mutation. For the PfMDR1 N86Y mutation, 72/121 samples (59.5%) had the sequence AAT at that position, indicating the presence of the wild-type allele (86N). However, 49/121 samples (40.5%) had a TAT codon, indicating the mutant allele (Y) at position 86. This study shows that pyrosequencing could be useful as a high throughput, rapid, and sensitive assay for the detection of specific single nucleotide polymorphisms in drug-resistant P. falciparum strains. This will help health authorities in malaria-endemic regions to adopt new malaria control strategies that will be applicable for diagnostic and drug resistance assays for malaria and other life-threatening pathogens that are endemic in their respective countries.

Regulatory T cells in infection

Infectious agents have intimately co-evolved with the host immune system, acquiring a portfolio of highly sophisticated mechanisms to modulate immunity. Among the common strategies developed by viruses, bacteria, protozoa, helminths, and fungi is the manipulation of the regulatory T cell network in order to favor pathogen survival and transmission. Treg activity also benefits the host in many circumstances by controlling immunopathogenic reactions to infection. Interestingly, some pathogens are able to directly induce the conversion of naive T cells into suppressive Foxp3-expressing Tregs, while others activate pre-existing natural Tregs, in both cases repressing pathogen-specific effector responses. However, Tregs can also act to promote immunity in certain settings, such as in initial stages of infection when effector cells must access the site of infection, and subsequently in ensuring generation of effector memory. Notably, there is little current information on whether infections selectively drive pathogen-specific Tregs, and if so whether these cells are also reactive to self-antigens. Further analysis of specificity, together with a clearer picture of the relative dynamics of Treg subsets over the course of disease, should lead to rational strategies for immune intervention to optimize immunity and eliminate infection.

TLR9 and endogenous adjuvants of the whole blood-stage malaria vaccine

Vaccination has been a successful tool in the protection against many infectious diseases, and recent advances in biotechnology have created new techniques and strategies to produce safe and efficacious vaccines for human use. However, developing a protective vaccine against malaria has been a challenge. In this article, we focus on an old approach with some new modifications, the so-called whole-parasite vaccination strategy against blood-stage Plasmodium falciparum, the deadliest human malarial agent. In addition, we discuss recent developments in our understanding of how the endogenous adjuvant activity in the parasites, which functions via Toll-like receptor 9, acts as a double-edged sword between protective vaccination and pathological responses against malaria infection.