Influence of tumor necrosis factor-alpha on the ability of monocytes and lymphocytes to destroy intraerythrocytic Plasmodium falciparum in vitro

Trichinella spiralis excretory/secretory products from adult worms inhibit NETosis and regulate the production of cytokines from neutrophils

Upon encountering exogenous pathogens, polymorphonucleocytes (PMNs) engage in various processes to destroy them, including releasing neutrophil extracellular traps (NETs) that trap pathogens and induce phagocytosis and cytokine production. Parasites have unique strategies with which to evade the host's immune response. However, the strategy employed by Trichinella spiralis in response to the reaction of PMNs has yet to be elucidated. This study explored the effect of excretory/secretory products (ESP) on three major functions: NETs, phagocytosis, and cytokine production. Specifically, PMNs were pre-treated with the ESP of 3-day-old adults and then stimulated with phorbol 12-myristate 13-acetate (PMA). We found that in PMNs pretreated with ESP, PMA-induced NET generation was suppressed by ESP. ROS production is a hallmark of PMA-induced NETosis. The LDH assay results showed that ESP inhibits NETs by suppressing ROS rather than promoting PMN death. Furthermore, ESP enhanced Escherichia coli engulfment by PMNs, improving overall phagocytic function. Finally, cytokine analysis revealed an increase in pro-inflammatory cytokine IL-1β, and other cytokines (IL-10, TNF-α), while IL-4 displayed a significant reduction. In conclusion, this study has unraveled T. spiralis' evasion and regulation mechanisms against innate immune cells, providing insights into parasite strategies to manipulate host immunity, potentially informing new treatments for NET-related autoimmune diseases.

Quantification of lipid bodies in monocytes from patients with periodontitis

OBJECTIVES

For the first time in the history of periodontics, the production of lipid bodies by monocytes was assessed from blood of patients with periodontitis in comparison to systemically healthy individuals. The purpose of this study was to compare the lipid body frequency within monocytes between healthy patients and those with periodontal disease.

MATERIALS AND METHODS

A total of 30 participants (11 males and 19 females), were divided between orally healthy control subjects (C, n = 16) and periodontitis subjects (P, n = 14), in a cross-sectional study. Both groups were systemically healthy. The following clinical periodontal parameters were assessed: probing depth, clinical attachment level, visible plaque index and gingival bleeding on probing index. Blood samples were collected to obtain monocytes containing lipid bodies, which were analyzed by light microscopy.

RESULTS

The periodontitis group demonstrated a higher corpuscular index than the control group (nonopsonized p = .0296 or opsonized p = .0459; Mann-Whitney). The frequency of monocyte cells containing lipid bodies (basal p = .0147, opsonized p = .0084 or nonopsonized, p = .026; Mann-Whitney) was also higher compared to those observed in healthy individuals.

CONCLUSIONS

The data suggest that periodontitis may contribute to a higher production of lipid bodies. It was also hypothesized that a major production of lipid bodies by monocytes in severe periodontitis, compared to orally healthy subjects, could interfere with the innate immune response or represents a higher reservoir of cholesterol esters within macrophages and a major risk to systemic implications, such as atherosclerosis.

Vaccination With Sporozoites: Models and Correlates of Protection

Despite continuous efforts, the century-old goal of eradicating malaria still remains. Multiple control interventions need to be in place simultaneously to achieve this goal. In addition to effective control measures, drug therapies and insecticides, vaccines are critical to reduce mortality and morbidity. Hence, there are numerous studies investigating various malaria vaccine candidates. Most of the malaria vaccine candidates are subunit vaccines. However, they have shown limited efficacy in Phase II and III studies. To date, only whole parasite formulations have been shown to induce sterile immunity in human. In this article, we review and discuss the recent developments in vaccination with sporozoites and the mechanisms of protection involved.

Environmental aspects related to tuberculosis and intestinal parasites in a low-income community of the Brazilian Amazon

We carried out a cross-sectional study from January to December 2015 on 1,425 inhabitants from a floating population in the Brazilian Amazon (Murinin district, Pará State) to describe the population-based prevalence of tuberculosis (TB) from 2011 to 2014, recent TB contacts (rCts) latently infected with Mycobacterium tuberculosis (LTBI) , the coverage of the local health network, socio-environmental factors, and frequency of intestinal parasitic infection (IPI). We found that the sanitary structure was inadequate, with latrines being shared with other rooms within the same accommodation; well water was the main source of water, and 48% of families had low incomes. The average rate of TB was 105/100, 000 inhabitants per year; one third of TB patients had been household contacts of infected individuals in the past, and 23% of rCts were LTBI. More than half (65%) of 44% of the stools examined (representing 76% of the housing) had IPIs; the highest prevalence was of fecal-oral transmitted protozoa (40%, Giardia intestinalis ), followed by soil-transmitted helminths (23%). TB transmission may be related to insufficient disease control of rCts, frequent relocation, and underreporting. Education, adopting hygienic habits, improving sanitation, provision of a treated water supply and efficient sewage system, further comprehensive epidemiological surveillance of those who enter and leave the community and resources for basic treatment of IPIs are crucial in combating the transmission of these neglected diseases.

IgG opsonization of merozoites: multiple immune mechanisms for malaria vaccine development

Global eradication of the human-infecting malaria parasite Plasmodium falciparum, the major cause of malaria mortality, is unlikely to be achieved without an effective vaccine. However, our limited understanding of how protective immune responses target malaria parasites in humans, and how to best elicit these immune responses through vaccination, has hampered vaccine development. The red blood cell invading stage of the parasite lifecycle (merozoite) displays antigens that are attractive vaccine candidates as they are accessible to antibodies and raise high antibody titres in naturally immune individuals. The number of merozoite antigens that elicit an immune response, and their structural and functional diversity, has led to a large number of lead antigens being pursued as vaccine candidates. Despite being seemingly spoilt for choice in terms of vaccine candidates, there is still a lack of consensus on exactly how merozoite antibodies reduce parasitemia and malaria disease. In this review we describe the various immune mechanisms that can result from IgG opsonization of merozoites, and highlight recent developments that support a role for these functional antibodies in naturally acquired and vaccine-induced immunity.

Differences in the modulation of reactive species, lipid bodies, cyclooxygenase-2, 5-lipoxygenase and PPAR-γ in cerebral malaria-susceptible and resistant mice

Proinflammatory responses are associated with the severity of cerebral malaria. NO, H₂O₂, eicosanoid and PPAR-γ are involved in proinflammatory responses, but regulation of these factors is unclear in malaria. This work aimed to compare the expression of eicosanoid-forming-enzymes in cerebral malaria-susceptible CBA and C57BL/6 and -resistant BALB/c mice. Mice were infected with Plasmodium berghei ANKA, and the survival rates and parasitemia curves were assessed. On the sixth day post-infection, cyclooxygenase-2 and 5-lipoxygenase in brain sections were assessed by immunohistochemistry, and, NO, H₂O₂, lipid bodies, and PPAR-γ expression were assessed in peritoneal macrophages. The C57BL/6 had more severe disease with a lower survival time, higher parasitemia and lower production of plasmodicidal NO and H₂O₂ molecules than BALB/c. Enhanced COX-2 and 5-LOX expression were observed in brain tissue cells and vessels from C57BL/6 mice, and these mice expressed higher constitutive PPAR-γ levels. There was no translocation of PPAR-γ from cytoplasm to nucleus in macrophages from these mice. CBA mice had enhanced COX-2 expression in brain tissue cells and vessels and also lacked PPAR-γ cytoplasm-to-nucleus translocation. The resistant BALB/c mice presented higher survival time, lower parasitemia and higher NO and H₂O₂ production on the sixth day post-infection. These mice did not express either COX-2 or 5-LOX in brain tissue cells and vessels. Our data showed that besides the high parasite burden and lack of microbicidal molecules, an imbalance with high COX-2 and 5-LOX eicosanoid expression and a lack of regulatory PPAR-γ cytoplasm-to-nucleus translocation in macrophages were observed in mice that develop cerebral malaria.

Ambivalent Outcomes of Cell Apoptosis: A Barrier or Blessing in Malaria Progression

The life cycle of Plasmodium in two evolutionary distant hosts, mosquito, and human, is a complex process. It is regulated at various stages of developments by a number of diverged mechanisms that ultimately determine the outcome of the disease. During the development processes, Plasmodium invades a variety of cells in two hosts. The invaded cells tend to undergo apoptosis and are subsequently removed from the system. This process also eliminates numerous parasites along with these apoptotic cells as a part of innate defense against the invaders. Plasmodium should escape the invaded cell before it undergoes apoptosis or it should manipulate host cell apoptosis for its survival. Interestingly, both these phenomena are evident in Plasmodium at different stages of development. In addition, the parasite also exhibits altruistic behavior and triggers its own killing for the selection of the best ‘fit’ progeny, removal of the ‘unfit’ parasites to conserve the nutrients and to support the host survival. Thus, the outcomes of cell apoptosis are ambivalent, favorable as well as unfavorable during malaria progression. Here we discuss that the manipulation of host cell apoptosis might be helpful in the regulation of Plasmodium development and will open new frontiers in the field of malaria research.

The Plasmodium bottleneck: malaria parasite losses in the mosquito vector

Nearly one million people are killed every year by the malaria parasite Plasmodium. Although the disease-causing forms of the parasite exist only in the human blood, mosquitoes of the genus Anopheles are the obligate vector for transmission. Here, we review the parasite life cycle in the vector and highlight the human and mosquito contributions that limit malaria parasite development in the mosquito host. We address parasite killing in its mosquito host and bottlenecks in parasite numbers that might guide intervention strategies to prevent transmission.

Enhanced neutrophil phagocytic capacity in rheumatoid arthritis related to the autoantibodies rheumatoid factor and anti-cyclic citrullinated peptides

Background

There is no consensus on the mechanisms by which anti-cyclic citrullinated peptide antibodies (anti-CCP) and rheumatoid factor (RF) influence the pathogenesis of rheumatoid arthritis (RA). The current study verified if the presence of RF or anti-CCP is associated with phagocytic capacity and reactive oxygen species (ROS) production by phagocytes in RA patients to better clarify the role played by these antibodies in pathogenesis of the disease.

Methods

A cohort of 30 RA patients followed from early stages of the disease were characterized by positivity for RF or anti-CCP, disease activity score (DAS-28), health assessment questionnaire (HAQ), use of synthetic or biologic therapy, lifestyle, comorbidities and radiographic erosions. Phagocytic capacity against Saccharomyces cerevisiae and superoxide anion production were assessed in RA patients and compared with 20 healthy controls. Phagocytic capacity and superoxide anion production were also compared between RF- and anti-CCP-positive and -negative RA patients.

Results

Anti-CCP- and RF-positive RA patients had higher neutrophil phagocytic capacity than anti-CCP- (p = 0.005) and RF (p = 0.005)-negative individuals through pattern-recognition receptors. As assessed via pattern recognition or opsonin receptors, neutrophils and monocytes from RA patients presented overall higher phagocytic capacity than neutrophils and monocytes from healthy controls (p < 0.05). Furthermore, RA patients also showed a higher capacity for producing cytotoxic oxygen radicals (p = 0.0026). Phagocytosis and superoxide anion production did not correlate with any of the clinical variables analyzed in this study.

Conclusions

This study showed increased phagocytosis by neutrophils in RA patients who were positive for anti-CCP and RF autoantibodies. Furthermore, there was an overall hyperactivation of the phagocytes in RA patients. Our data suggest that anti-CCP and RF may indirectly enhance the inflammation cascade involving neutrophils and may indirectly sustain tissue damage in RA. Targeting the production of these autoantibodies may be a promising strategy in the management of RA.

An autochthonous case of severe Plasmodium knowlesi malaria in Thailand

A 58-year-old Thai man was infected with Plasmodium knowlesi in Chantaburi Province, eastern Thailand. In addition to pyrexia, the patient developed hypotension, renal failure, jaundice, and severe thrombocytopenia. The parasitemia at the time of admission was 16.67% or ∼503,400 parasites/μL. With artesunate treatment and supportive care, the patient recovered uneventfully. The occurrence of complicated knowlesi malaria in a low-endemic area underscores the risk of high morbidity from this simian malaria.

Opsonic phagocytosis of Plasmodium falciparum merozoites: mechanism in human immunity and a correlate of protection against malaria

BACKGROUND

An understanding of the mechanisms mediating protective immunity against malaria in humans is currently lacking, but critically important to advance the development of highly efficacious vaccines. Antibodies play a key role in acquired immunity, but the functional basis for their protective effect remains unclear. Furthermore, there is a strong need for immune correlates of protection against malaria to guide vaccine development.

METHODS

Using a validated assay to measure opsonic phagocytosis of Plasmodium falciparum merozoites, we investigated the potential role of this functional activity in human immunity against clinical episodes of malaria in two independent cohorts (n = 109 and n = 287) experiencing differing levels of malaria transmission and evaluated its potential as a correlate of protection.

RESULTS

Antibodies promoting opsonic phagocytosis of merozoites were cytophilic immunoglobulins (IgG1 and IgG3), induced monocyte activation and production of pro-inflammatory cytokines, and were directed against major merozoite surface proteins (MSPs). Consistent with protective immunity in humans, opsonizing antibodies were acquired with increasing age and malaria exposure, were boosted on re-infection, and levels were related to malaria transmission intensity. Opsonic phagocytosis was strongly associated with a reduced risk of clinical malaria in longitudinal studies in children with current or recent infections. In contrast, antibodies to the merozoite surface in standard immunoassays, or growth-inhibitory antibodies, were not significantly associated with protection. In multivariate analyses including several antibody responses, opsonic phagocytosis remained significantly associated with protection against malaria, highlighting its potential as a correlate of immunity. Furthermore, we demonstrate that human antibodies against MSP2 and MSP3 that are strongly associated with protection in this population are effective in opsonic phagocytosis of merozoites, providing a functional link between these antigen-specific responses and protection for the first time.

CONCLUSIONS

Opsonic phagocytosis of merozoites appears to be an important mechanism contributing to protective immunity in humans. The opsonic phagocytosis assay appears to be a strong correlate of protection against malaria, a valuable biomarker of immunity, and provides a much-needed new tool for assessing responses to blood-stage malaria vaccines and measuring immunity in populations.

Protein S-nitrosylation in Plasmodium falciparum

AIMS

Due to its life in different hosts and environments, the human malaria parasite Plasmodium falciparum is exposed to oxidative and nitrosative challenges. Nitric oxide (NO) and NO-derived reactive nitrogen species can constitute nitrosative stress and play a major role in NO-related signaling. However, the mode of action of NO and its targets in P. falciparum have hardly been characterized. Protein S-nitrosylation (SNO), a posttranslational modification of protein cysteine thiols, has emerged as a principal mechanism by which NO exerts diverse biological effects. Despite its potential importance, SNO has hardly been studied in human malaria parasites. Using a biotin-switch approach coupled to mass spectrometry, we systemically studied SNO in P. falciparum cell extracts.

RESULTS

We identified 319 potential targets of SNO that are widely distributed throughout various cellular pathways. Glycolysis in the parasite was found to be a major target, with glyceraldehyde-3-phosphate dehydrogenase being strongly inhibited by S-nitrosylation of its active site cysteine. Furthermore, we show that P. falciparum thioredoxin 1 (PfTrx1) can be S-nitrosylated at its nonactive site cysteine (Cys43). Mechanistic studies indicate that PfTrx1 possesses both denitrosylating and transnitrosylating activities mediated by its active site cysteines and Cys43, respectively.

INNOVATION

This work provides first insights into the S-nitrosoproteome of P. falciparum and suggests that the malaria parasite employs the thioredoxin system to deal with nitrosative challenges.

CONCLUSION

Our results indicate that SNO may influence a variety of metabolic processes in P. falciparum and contribute to our understanding of NO-related signaling processes and cytotoxicity in the parasites.

Meglumine antimonate treatment enhances phagocytosis and TNF-α production by monocytes in human cutaneous leishmaniasis

This work evaluated phagocytic function, hydrogen peroxide (H(2)O(2)), TNF-α and IL-10 production by monocytes and serum INF-γ levels in New World human cutaneous leishmaniasis and the influence of meglumine antimonate treatment on these immune functions. The phagocytic capacity of monocytes in untreated Leishmania-infected individuals was significantly (2.5 times) lower than that of healthy controls, and antimonial treatment increased the phagocytosis by monocytes by about five times at the end of therapy. The leishmaniasis patients showed 3.9 times higher H(2)O(2) production than controls and treatment with meglumine antimonate did not influence the production of H(2)O(2), which remained enhanced until the end of treatment. Individuals with leishmaniasis showed 6.3 times lower TNF-α production than healthy individuals and meglumine antimonate treatment caused a significant increment (11.9 times) in its production. INF-γ serum levels were higher in Leishmania-infected individuals than healthy controls, and the production of IL-10 by monocytes was not influenced by infection or antimonial treatment. Enhancement of monocyte functions by the antimonial treatment suggests that the immunomodulatory effects of the drug may also play a part in the way meglumine antimonate acts against the parasite in human leishmaniasis, by directly increasing phagocytosis and TNF-α production.

Sex and Death: The Effects of Innate Immune Factors on the Sexual Reproduction of Malaria Parasites

Malaria parasites must undergo a round of sexual reproduction in the blood meal of a mosquito vector to be transmitted between hosts. Developing a transmission-blocking intervention to prevent parasites from mating is a major goal of biomedicine, but its effectiveness could be compromised if parasites can compensate by simply adjusting their sex allocation strategies. Recently, the application of evolutionary theory for sex allocation has been supported by experiments demonstrating that malaria parasites adjust their sex ratios in response to infection genetic diversity, precisely as predicted. Theory also predicts that parasites should adjust sex allocation in response to host immunity. Whilst data are supportive, the assumptions underlying this prediction – that host immune responses have differential effects on the mating ability of males and females – have not yet been tested. Here, we combine experimental work with theoretical models in order to investigate whether the development and fertility of male and female parasites is affected by innate immune factors and develop new theory to predict how parasites' sex allocation strategies should evolve in response to the observed effects. Specifically, we demonstrate that reactive nitrogen species impair gametogenesis of males only, but reduce the fertility of both male and female gametes. In contrast, tumour necrosis factor-α does not influence gametogenesis in either sex but impairs zygote development. Therefore, our experiments demonstrate that immune factors have complex effects on each sex, ranging from reducing the ability of gametocytes to develop into gametes, to affecting the viability of offspring. We incorporate these results into theory to predict how the evolutionary trajectories of parasite sex ratio strategies are shaped by sex differences in gamete production, fertility and offspring development. We show that medical interventions targeting offspring development are more likely to be ‘evolution-proof’ than interventions directed at killing males or females. Given the drive to develop medical interventions that interfere with parasite mating, our data and theoretical models have important implications.

Malaria and related parasites cause some of the most serious infectious diseases of humans, domestic animals and wildlife. To be transmitted, these parasites produce male and female sexual stages that differentiate into gametes and mate when taken up in a mosquito blood meal. Despite the need to develop a transmission-blocking intervention, remarkably little is understood about the evolution of parasite mating strategies. However, recent research demonstrates that producing the right ratio of male to female stages is central to mating success. Evolutionary theory predicts that sex ratios are adjusted in line with a variety of factors that affect mating success, including host immunity. We test this theory by investigating whether ubiquitous immune factors differentially affect the production and fertility of males and females. Our experiments demonstrate that immune factors have complex, sex-specific effects, from reducing gamete production to affecting offspring viability. We use these results to generate theory predicting how such effects shape the evolutionary trajectories of parasite sex ratio strategies. Given the drive to develop medical interventions that prevent transmission by blocking parasite mating, our results have important implications. Specifically, we suggest that medical interventions targeting offspring development are more likely to be ‘evolution-proof’ than interventions with sex-specific effects.

FcgammaRIIB in autoimmunity and infection: evolutionary and therapeutic implications

FcgammaRIIB is the only inhibitory Fc receptor. It controls many aspects of immune and inflammatory responses, and variation in the gene encoding this protein has long been associated with susceptibility to autoimmune disease, particularly systemic lupus erythematosus (SLE). FcgammaRIIB is also involved in the complex regulation of defence against infection. A loss-of-function polymorphism in FcgammaRIIB protects against severe malaria, the investigation of which is beginning to clarify the evolutionary pressures that drive ethnic variation in autoimmunity. Our increased understanding of the function of FcgammaRIIB also has potentially far-reaching therapeutic implications, being involved in the mechanism of action of intravenous immunoglobulin, controlling the efficacy of monoclonal antibody therapy and providing a direct therapeutic target.

A defunctioning polymorphism in FCGR2B is associated with protection against malaria but susceptibility to systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease more prevalent in people of African and Asian origin than Caucasian origin. FcgammaRIIb is an inhibitory Fc receptor with a critical role in immune regulation. Mouse data suggest that FcgammaRIIb deficiency increases susceptibility to autoimmune disease but protects against infection. We show that a SNP in human FCGR2B that abrogates receptor function is strongly associated with susceptibility to SLE in both Caucasians and Southeast Asians. The minor allele of this SNP is more common in Southeast Asians and Africans, populations from areas where malaria is endemic, than in Caucasians. We show that homozygosity for the minor allele is associated with substantial protection against severe malaria in an East African population (odds ratio = 0.56; P = 7.1 x 10(-5)). This protective effect against malaria may contribute to the higher frequency of this SNP and hence, SLE in Africans and Southeast Asians.

Stages of in vitro phagocytosis of Plasmodium falciparum-infected erythrocytes by human monocytes

Monocytes/macrophages play a critical role in the defense mechanisms against malaria parasites, and are the main cells responsible for the elimination of malaria parasites from the blood circulation. We carried out a microscope-aided evaluation of the stages of in vitro phagocytosis of Plasmodium falciparum-infected erythrocytes, by human monocytes. These cells were obtained from healthy adult individuals by means of centrifugation through a cushion of Percoll density medium and were incubated with erythrocytes infected with Plasmodium falciparum that had previously been incubated with a pool of anti-plasmodial immune serum. We described the stages of phagocytosis, starting from adherence of infected erythrocytes to the phagocyte membrane and ending with their destruction within the phagolisosomes of the monocytes. We observed that the different erythrocytic forms of the parasite were ingested by monocytes, and that the process of phagocytosis may be completed in around 30 minutes. Furthermore, we showed that phagocytosis may occur continuously, such that different phases of the process were observed in the same phagocyte.

Meglumine antimonate directly increases phagocytosis, superoxide anion and TNF-alpha production, but only via TNF-alpha it indirectly increases nitric oxide production by phagocytes of healthy individuals, in vitro

Leishmania has developed mechanisms to escape from immune defense of phagocytes by inhibiting microbicidal oxygen and nitrogen radicals. This work evaluated the influence of meglumine antimonate (Sb(V)) on the phagocyte functions involved in the defense against leishmania, through phagocytosis, reactive oxygen, nitrogen and TNF-alpha production in the absence or presence of the drug, in vitro. Meglumine antimonate increased the number of Saccharomyces cerevisiae ingested by monocyte and the percentage of these cells engaged in phagocytosis, which resulted in an increase of the monocyte phagocytic index by 158%. Meglumine antimonate also increased the number of S. cerevisiae ingested by neutrophil and the percentage of these cells engaged in phagocytosis, increasing the neutrophil phagocytic index by 219%. The median of percent reduction of NBT was significantly increased after treatment with this pentavalent antimony from 89.5% to 96.5%. Meglumine antimonate had no influence on nitric oxide production, but it significantly increased the mean+/-SEM production of tumor necrosis factor by 230%. However, monocytes incubated with TNF significantly increased NO production. This antimonial increased the phagocytic capacity of monocytes and neutrophils and enhanced superoxide anion production by phagocytes, which represent the first line of defense against the parasite. Furthermore, meglumine antimonate increased TNF, and via this cytokine, it may also indirectly increase NO production. Our data suggest that these immunomodulatory effects of meglumine antimonate may play a role in fighting leishmania and that meglumine antimonate provides the phagocytes with a mechanism that prevents leishmania from escaping immune defense.

The immunological challenges of malaria vaccine development

Malaria remains an important public health problem throughout the tropical world causing immense human suffering and impeding economic development. Despite extensive research for > 100 years, options for preventing malaria remain limited to vector control and chemoprophylaxis. The complexity of the organism and its life cycle have, thus far, thwarted vaccine development and exacerbated the perennial problems of drug resistance. Nevertheless, development of a vaccine against malaria that reduces morbidity and mortality, and ideally also reduces transmission, has long been seen as an essential component of a sustainable malaria control strategy. In this article the authors review the biological challenges of malaria vaccine development, summarise some of the recent advances and offer some immunological insights which might facilitate further research.

Systemic lupus erythematosus-associated defects in the inhibitory receptor FcgammaRIIb reduce susceptibility to malaria

Polygenic autoimmune diseases, such as systemic lupus erythematosus (SLE), are a significant cause of morbidity and mortality worldwide. In recent years, functionally important genetic polymorphisms conferring susceptibility to SLE have been identified, but the evolutionary pressures driving their retention in the gene pool remain elusive. A defunctioning, SLE-associated polymorphism of the inhibitory receptor FcgammaRIIb is found at an increased frequency in African and Asian populations, broadly corresponding to areas where malaria is endemic. Here, we show that FcgammaRIIb-deficient mice have increased clearance of malarial parasites (Plasmodium chabaudi chabaudi) and develop less severe disease. In vitro, the human lupus associated FcgammaRIIb polymorphism enhances phagocytosis of Plasmodium falciparum-infected erythrocytes. These results demonstrate that FcgammaRIIb is important in controlling the immune response to malarial parasites and suggests that the higher frequency of human FcgammaRIIb polymorphisms predisposing to SLE in Asians and Africans may be maintained because these variants reduce susceptibility to malaria.

The molecular basis of paediatric malarial disease

Severe falciparum malaria is an acute systemic disease that can affect multiple organs, including those in which few parasites are found. The acute disease bears many similarities both clinically and, potentially, mechanistically, to the systemic diseases caused by bacteria, rickettsia, and viruses. Traditionally the morbidity and mortality associated with severe malarial disease has been explained in terms of mechanical obstruction to vascular flow by adherence to endothelium (termed sequestration) of erythrocytes containing mature-stage parasites. However, over the past few decades an alternative ‘cytokine theory of disease’ has also evolved, where malarial pathology is explained in terms of a balance between the pro- and anti-inflammatory cytokines. The final common pathway for this pro-inflammatory imbalance is believed to be a limitation in the supply and mitochondrial utilisation of energy to cells. Different patterns of ensuing energy depletion (both temporal and spatial) throughout the cells in the body present as different clinical syndromes. This chapter draws attention to the over-arching position that inflammatory cytokines are beginning to occupy in the pathogenesis of acute malaria and other acute infections. The influence of inflammatory cytokines on cellular function offers a molecular framework to explain the multiple clinical syndromes that are observed during acute malarial illness, and provides a fresh avenue of investigation for adjunct therapies to ameliorate the malarial disease process.

Human malarial disease: a consequence of inflammatory cytokine release

Malaria causes an acute systemic human disease that bears many similarities, both clinically and mechanistically, to those caused by bacteria, rickettsia, and viruses. Over the past few decades, a literature has emerged that argues for most of the pathology seen in all of these infectious diseases being explained by activation of the inflammatory system, with the balance between the pro and anti-inflammatory cytokines being tipped towards the onset of systemic inflammation. Although not often expressed in energy terms, there is, when reduced to biochemical essentials, wide agreement that infection with falciparum malaria is often fatal because mitochondria are unable to generate enough ATP to maintain normal cellular function. Most, however, would contend that this largely occurs because sequestered parasitized red cells prevent sufficient oxygen getting to where it is needed. This review considers the evidence that an equally or more important way ATP deficiency arises in malaria, as well as these other infectious diseases, is an inability of mitochondria, through the effects of inflammatory cytokines on their function, to utilise available oxygen. This activity of these cytokines, plus their capacity to control the pathways through which oxygen supply to mitochondria are restricted (particularly through directing sequestration and driving anaemia), combine to make falciparum malaria primarily an inflammatory cytokine-driven disease.

Effects of pravastatin on the in vitro phagocytic function and hydrogen peroxide production by monocytes of healthy individuals

Macrophages play a part in pathogenesis of atherosclerosis, oxidizing LDL-cholesterol and transforming themselves in foam cells and producing free radicals of oxygen that may also oxidize LDL-cholesterol. HMG-CoA reductase inhibitors are very efficient in long-term control of atherogenesis acting by different mechanisms not fully established. Thus, we investigated the in vitro influence of pravastatin on phagocytosis and hydrogen peroxide production by monocytes of healthy individuals. Phagocytosis of Saccharomyces erevisiae by peripheral blood monocytes of 20 healthy individuals was assessed in the absence or presence of pravastatin. Hydrogen peroxide production was assessed based on the horseradish peroxidase-dependent oxidation of phenol red method. Pravastatin had no influence on phagocytosis through scavenger receptors, while it decreased by 20% the mean+/-SD phagocytic index of monocytes through complement receptors, from 141+/-77 to 113+/-56 (p=0.017), due to a decrease in the number of particles ingested by monocytes, from 2.1+/-0.5 to 1.7+/-0.3 (p=0.003). This statin also decreased the baseline production of hydrogen peroxide, by 7.7%, from 0.098+/-0.013 to 0.091+/-0.013 (OD by 2x10(5) monocytes per hour) (p=0.025). Pravastatin was able to decrease the phagocytosis through complement receptors and caused a decrease in the production of hydrogen peroxide by monocytes. It is possible this statin may directly inhibit the development of atherosclerotic plaque and its instability dependent on phagocytosis and the presence of reactive species of oxygen.

Acute and chronic influence of hemodialysis according to the membrane used on phagocytic function of neutrophils and monocytes and pro-inflammatory cytokines production in chronic renal failure patients

This work evaluated the phagocytic capacity of monocytes and neutrophils, and tumor necrosis factor-alpha, interleukin 6, 1 and 8 serum levels in chronic renal failure patients under peritoneal dialysis and hemodialysis treatment, compared with chronic renal failure patients without dialysis treatment and healthy individuals, in order to contribute to a better understanding of the action of these therapies on the evolution of chronic renal failure patients. All patients with chronic renal failure (under dialysis or not) showed decreased phagocytic capacity of neutrophils and monocytes. All those in hemodialysis (cellulose acetate or polysulfone membranes) showed a decreased phagocytic capacity. The phagocytic index for neutrophil was 13 times lower than that of the control group for both membranes, whereas for monocytes, only those using polysulfone membrane showed a significant decrease of 4.9 times in phagocytic capacity. There was an acute stimulation of the phagocytosis by neutrophils after a single session of dialysis with both types of membrane, while only cellulose acetate membrane decreased the phagocytic index of monocytes after the hemodialysis session. Patients using cellulose acetate showed a chronic increase in tumor necrosis factor-alpha serum levels, while those using polysulfone showed a chronic increase in interleukin 6. After a single hemodialysis procedure, no acute effect of the treatment on tumor necrosis factor-alpha and interleukin 6 levels was identified. The decreased phagocytic function of neutrophils and monocytes may account for the high levels of susceptibility of chronic renal failure patients to infections with pyogenic bacteria and tuberculosis. Furthermore, inflammatory activity may occur with both types of membrane studied, suggesting that it will be useful for these patients to evaluate some anti-inflammatory or anti-cytokine therapies against tumor necrosis factor-alpha and interleukin 6, in order to avoid cardiovascular complication.

Thalidomide influences the function of macrophages and increases the survival of Plasmodium berghei-infected CBA mice

Malaria remains a major cause of morbidity and mortality in vast areas of the world, mainly due to the severe forms of Plasmodium falciparum infection. The exacerbated immune response, with increased production of TNF and reactive nitrogen and oxygen intermediates, plays a role in the complex pathogenesis of the disease. It is recognised that thalidomide decreases TNF production and may modulate several functions of the immune system. This work evaluated the influence of thalidomide on macrophage functions, and its ability to protect against severe disease. Plasmodium berghei ANKA-infected mice were (n=11) or were not (n=10) intra-gastric treated with thalidomide (150 mg/kg per day), and two other control groups not infected with the parasite were (n=8) or were not (n=10) treated with the drug, and macrophage production of hydrogen peroxide and nitric oxide, and phagocytosis were assessed on the eighth day post-infection. Thalidomide increased the survival time of infected mice, in parallel with a 26.5% increase of the mean of macrophage phagocytic index, and augmented in 13% the mean of the production of hydrogen peroxide and in 45% the mean of nitric oxide production by macrophages related to the non-treated P. berghei-infected mice. Our data indicate that thalidomide improves the outcome of P. berghei ANKA-infected CBA mice and suggest that this drug could represent a new alternative to be associated to antimalarial drugs to decrease the morbidity and mortality of severe malaria in non-pregnant individuals.

Glycosylphosphatidylinositols in malaria pathogenesis and immunity: potential for therapeutic inhibition and vaccination

Glycosylphosphatidylinositols (GPIs) are found in the outer cell membranes of all eukaryotes. GPIs anchor a diverse range of proteins to the surface of Plasmodium falciparum, but may also exist free of protein attachment. In vitro and in vivo studies have established GPIs as likely candidate toxins in malaria, consistent with the prevailing paradigm that attributes induction of inflammatory cytokines, fever and other pathology to parasite toxins released when schizonts rupture. Although evolutionarily conserved, sufficient structural differences appear to exist that impart upon plasmodial GPIs the ability to activate second messengers in mammalian cells and elicit immune responses. In populations exposed to P. falciparum, the antibody response to purified GPIs is characterised by a predominance of immunoglobulin (Ig)G over IgM and an increase in the prevalence, level and persistence of responses with increasing age. It remains unclear, however, if these antibodies or other cellular responses to GPIs mediate anti-toxic immunity in humans; anti-toxic immunity may comprise either reduction in the severity of disease or maintenance of the malaria-tolerant state (i.e. persistent asymptomatic parasitaemia). P. falciparum GPIs are potentially amenable to specific therapeutic inhibition and vaccination; more needs to be known about their dual roles in malaria pathogenesis and protection for these strategies to succeed.

Differing phagocytic function of monocytes and neutrophils in Chagas' cardiopathy according to the presence or absence of congestive heart failure

We evaluated the in vitro phagocytic function and the production of microbicidal oxygen radicals by monocytes and neutrophils of 9 Chagas' heart disease subjects with heart failure and 9 without the syndrome in comparison with 11 healthy subjects, by assessing phagocytosis of Saccharomyces cerevisiae and NBT reduction by peripheral blood phagocytes. Phagocytic index of monocytes of chagasics without heart failure was significantly 6.7 and 10.6 times lower than those of controls and chagasics with the congestive syndrome, respectively, due to a lesser engagement in phagocytosis and to an inability of these cells to ingest particles. Neutrophils also show in chagasics without heart failure PI 11.2 and 19.8 times lower than that of controls and chagasics with heart failure, respectively. The percent of NBT reduction was normal and similar for the three groups. Balanced opposite effects of cardiovascular and immune disturbances may be acting in Chagas' disease subjects with heart failure paradoxically recovering the altered phagocytic function.

Novel microtechnique for assessment of postnatal maturation of the phagocytic function of neutrophils and monocytes

We describe a simple test for the evaluation of phagocytosis and provide a chart of reference values to evaluate normal phagocytosis by age. We assessed the postnatal maturation of phagocytic function of neutrophils and monocytes. Phagocytosis was evaluated in newborn children delivered vaginally or by cesarean section, infants, preschool children, schoolchildren, and adult subjects. Two drops of blood were placed on a microscope slide and incubated with Saccharomyces cerevisiae yeasts, and phagocytosis was evaluated by microscopy. Our technique showed results comparable to or better than those obtained by other usual techniques. The neutrophils of newborn children delivered by cesarean section showed a phagocytic capacity 45% higher than those of neonates delivered vaginally, whereas neutrophils from children in the latter group showed the lowest phagocytic capacity of all age groups. Phagocytosis by neutrophils reached the levels seen in adults at about the first year of life, while there were no important variations in phagocytosis by monocytes in the different age groups. The technique described is reliable and fast, uses only a few drops of blood, and allows better preservation of cell function due to the minimal manipulation to which the cells are submitted. The delayed maturation of the phagocytic function by neutrophils may account for the high levels of susceptibility of newborn and infant children to bacterial infections. This practical method of assessment of phagocytosis may allow the diagnosis of primary or secondary phagocytic deficiencies to be made more easily and may allow better monitoring and treatment of those with dysfunctions of these cells.

Relationship between erythrocytic immunity and T-cell subsets in patients with benign and malignant gastric ulcers

AIM: To investigate the variation and their relationship between erythrocytic immunity and T-cell subsets in patients with benign and malignant gastric ulcer (BGU and MGU) and to provide a basis for prevention and immune therapy.

METHODS: In 30 cases of BGU, 25 cases of MGU and 32 cases of normal control, RBC-C_3bRR, RBC-ICR and RBC-TRR were tested by immune adherence rosette method. T-cell subsets were tested by SAP assay.

RESULTS: RBC-C_3bRR and RBC-TRR remarkably declined in MGU group than those in BGU group and the control group (P < 0.01). The number fractions of CD3⁺, CD4⁺ and CD4⁺/CD8⁺ ratio were significantly lower in MGU group as compared with BGU group and control subjects (P < 0.05). The value of RBC-ICR and the percentage of CD8⁺ were the highest in MGU group. They were second in BGU group and the lowest in the control group (P < 0.05). The CD4⁺/CD8⁺ ratio was significantly correlated with the value of RBC-C_3bRR and RBC-TRR in the BGU and MGU groups (P < 0.01).

CONCLUSION: Both erythrocytic immunity and T-cell subsets may play an important role in the occurrence and development of the BGU and MGU. Erythrocytic immunity may regulate the activity of immune cells including T-cell subsets via some mechanisms. Erythrocytic immunity and T-cell subsets may have the immune prevention functions in patients with BGU and MGU.

Expression of tumour necrosis factor-alpha in the rat dental follicle

Tooth eruption requires the presence of the dental follicle, a loose connective tissue sac that surrounds each unerupted tooth. The follicle appears to regulate many of the cellular and molecular events of eruption, including the formation of osteoclasts needed to resorb alveolar bone to form an eruption pathway. To that end, the expression of the tumour necrosis factor-alpha (TNF-alpha) gene was examined in the dental follicle as a possible regulator of osteoclastogenesis. TNF-alpha was expressed slightly in the dental follicle of the first mandibular molar of the rat beginning at day 3 postnatally, but maximal expression was seen at day 9, a time that correlates with a slight burst of osteoclast formation seen at day 10 postnatally. In vitro, TNF-alpha was not expressed constitutively in the follicle cells but incubating them with interleukin 1alpha resulted in a strong expression of TNF-alpha after only 0.5h. TNF-alpha itself enhanced monocyte chemotactic protein 1 (MCP-1) and vascular endothelial growth factor (VEGF) gene expression. It also slightly decreased the expression of osteoprotegerin after 3-h incubation but this returned to the control level at 6h. MCP-1 and VEGF could aid in recruiting mononuclear cells (osteoclast precursors) to the dental follicle. In addition to the potential role of TNF-alpha in tooth eruption, this study suggests that the periodontal ligament derived from the dental follicle might have the capacity to synthesize TNF-alpha, and thereby contribute to the destructive events of periodontitis.

Immunity to asexual blood stage malaria and vaccine approaches

The development of a malaria vaccine seems to be a definite possibility despite the fact that even individuals with a life time of endemic exposure do not develop sterile immunity. An effective malaria vaccine would be invaluable in preventing malaria-associated deaths in endemic areas, especially amongst children less than 5 years of age and pregnant women. This review discusses our current understanding of immunity against the asexual blood stage of malaria - the stage that is responsible for the symptoms of the disease - and approaches to the design of an asexual blood stage vaccine.

The immune response to Plasmodium falciparum malaria

Malaria is still a major cause of severe disease which is responsible for millions of deaths, mostly in children under 5 years old, in tropical countries, especially sub-Saharan Africa. Complications of severe anaemia and cerebral malaria are thought to be the major cause of morbidity and mortality but recent evidence suggests that the host's immunological response could also contribute to the pathophysiology of the disease in human beings. Intensive studies of the immune response to malaria parasites in human beings have provided a wealth of information about the cells and cytokines implicated in the pathophysiology of survival and fatal outcome in severe infections. This review focuses on the pivotal role of macrophages and other important cellular effectors, molecules, and cytokines involved in the activation of the immune response at the different stages of human falciparum malaria. Our understanding of the putative mechanisms by which cytokines may mediate beneficial and harmful effects, through activation of phagocytic cells, could help to develop new treatment strategies, regardless of the emergence of parasite multidrug resistance.