Contribution of T Cells and Neutrophils in Protection of Young Susceptible Rats from Fatal Experimental Malaria

Role of human group IIA secreted phospholipase A2 in malaria pathophysiology: Insights from a transgenic mouse model

We previously showed that injection of recombinant human group IIA secreted phospholipase A₂ (hGIIA sPLA₂) to Plasmodium chabaudi-infected mice lowers parasitaemia by 20%. Here, we show that transgenic (TG) mice overexpressing hGIIA sPLA₂ have a peak of parasitaemia about 30% lower than WT littermates. During infection, levels of circulating sPLA₂, enzymatic activity and plasma lipid peroxidation were maximal at day-14, the peak of parasitaemia. Levels of hGIIA mRNA increased in liver but not in spleen and blood cells, suggesting that liver may contribute as a source of circulating hGIIA sPLA₂. Before infection, baseline levels of leukocytes and pro-inflammatory cytokines were higher in TG mice than WT littermates. Upon infection, the number of neutrophils, lymphocytes and monocytes increased and were maximal at the peak of parasitaemia in both WT and TG mice, but were higher in TG mice. Similarly, levels of the Th1 cytokines IFN-γ and IL-2 increased in WT and TG mice, but were 7.7- and 1.7-fold higher in TG mice. The characteristic shift towards Th2 cytokines was observed during infection in both WT and TG mice, with increased levels of IL-10 and IL-4 at day-14. The current data are in accordance with our previous in vitro findings showing that hGIIA kills parasites by releasing toxic lipids from oxidized lipoproteins. They further show that hGIIA sPLA₂ is induced during mouse experimental malaria and has a protective in vivo role, lowering parasitaemia by likely releasing toxic lipids from oxidized lipoproteins but also indirectly by promoting a more sustained innate immune response.

Comorbidity of Geo-Helminthes among Malaria Outpatients of the Health Facilities in Ethiopia: Systematic Review and Meta-Analysis

Background: Coinfection of malaria and intestinal helminths affects one third of the global population, largely among communities with severe poverty. The spread of these parasitic infections overlays in several epidemiological locations and the host shows different outcomes. This systematic review and meta-analysis determine the pooled prevalence of malaria and intestinal helminthiases coinfections among malaria suspected patients in Ethiopia. Methods: Primary studies published in English language were retrieved using appropriate search terms on Google Scholar, PubMed/MEDLINE, CINHAL, Scopus, and Embase. The Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) was used for critical appraisal of studies. A pooled statistical meta-analysis was conducted using STATA Version 14.0 software. The heterogeneity and publication bias were assessed using the I2 statistics and Egger’s test, respectively. Duval and Tweedie’s nonparametric trim and fill analysis using the random-effect analysis. The Random effects model was used to estimate the summary prevalence of comorbidity of malaria and soil transmitted helminthiases and the corresponding 95% confidence intervals (CI). The review protocol has registered in PROSPERO number CRD42019144803. Results: We identified ten studies (n = 6633 participants) in this study. The overall pooled result showed 13% of the ambulatory patients infected by malaria and intestinal helminths concurrently in Ethiopia. The pooled prevalence of Plasmodium falciparum and Plasmodium vivax, and mixed infections were 12, 30, and 6%, respectively. The most common intestinal helminth parasites detected were Hookworm, Ascaris lumbricoides, and Tirchuris trichiura. Conclusions: The comorbidity of malaria and intestinal helminths causes lower hemoglobin level leading to maternal anemia, preterm delivery, and still birth in pregnant women and lactating mother. School-aged children and neonates coinfected by plasmodium species and soil transmitted helminths develop cognitive impairment, protein energy malnutrition, low birth weight, small for gestational age, and gross motor delay. The Ministry of Health of Ethiopia and its international partners working on malaria elimination programs should give more emphasis to the effect of the interface of malaria and soil transmitted helminths, which calls for an integrated disease control and prevention.

Trichinella spiralis co-infection exacerbates Plasmodium berghei malaria-induced hepatopathy

Background

Although Plasmodium parasites and intestinal helminths share common endemic areas, the mechanisms of these co-infections on the host immune response remain not fully understood. Liver involvement in severe Plasmodium falciparum infections is a significant cause of morbidity and mortality. However, the effect of pre-existing Trichinella spiralis infection on the immune response and liver immune-pathogenesis in P. berghei ANKA (PbANKA)-infected mice needs to be elucidated.

Methods

Outbred Kunming mice were infected with T. spiralis and 9 days later were challenged with P. berghei ANKA (PbANKA), and the investigation occurred at 13 days after co-infection.

Results

Compared with PbANKA-mono-infected mice, T. spiralis + PbANKA-co-infected mice had similar survival rate but lower PbANKA parasitaemia; however, there were more severe hepatosplenomegaly, increased liver and spleen indexes, and increased liver pathology observed by hematoxylin and eosin staining; higher expression levels of galectin (Gal)-1, Gal-3, CD68⁺ macrophages, and elastase-positive neutrophils measured by immunohistochemical staining; upregulated mRNA expression levels of Gal-1, Gal-3, cytokines (interferon-gamma (IFNγ) and interleukin (IL)-6), and M1 macrophage polarization marker (inducible nitric oxide synthase (iNOS)) in the liver, and increased expression levels of Gal-1, IFNγ, IL-6, eosinophil cationic protein, eosinophil protein X, and M1 (IL-1β and iNOS) and M2 (Ym1) macrophage polarization markers in the spleen of co-infected mice detected by using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). In vitro study showed that compared with PbANKA-mono-infected mice, there were significantly increased expression levels of Gal-1, Gal-3, IL-6, IL-1β, and iNOS in the peritoneal macrophage isolated from co-infected mice detected by using qRT-PCR. Correlation analysis revealed significant positive correlations between Gal-3 and IL-1β in the peritoneal macrophages isolated from PbANKA-mono-infected mice, between Gal-3 and IFNγ in the spleen of co-infected mice, and between Gal-1 and Ym1 in the peritoneal macrophages isolated from co-infected mice.

Conclusions

Our data indicate that pre-existing infection of T. spiralis may suppress P. berghei parasitaemia and aggravate malaria-induced liver pathology through stimulating Gal-1 and Gal-3 expression, activating macrophages, neutrophils, and eosinophils, and promoting mediator release and cytokine production.

Differential Gene Expression Profile of Human Neutrophils Cultured with Plasmodium falciparum-Parasitized Erythrocytes

Neutrophils (PMNs) are the most abundant cellular component of our innate immune system, where they play central roles in the pathogenesis of and resistance to a broad range of diseases. However, their roles in malarial infection remain poorly understood. Therefore, we examined the transcriptional gene profile of human PMNs in response to Plasmodium falciparum-parasitized erythrocytes (iRBCs) by using oligonucleotide microarrays. Results revealed that PMNs induced a broad and vigorous set of changes in gene expression in response to malarial parasites, represented by 118 upregulated and 216 downregulated genes. The transcriptional response was characterized by the upregulation of numerous genes encoding multiple surface receptors, proteins involved in signal transduction pathways, and defense response proteins. This response included a number of genes which are known to be involved in the pathogenesis of malaria and other inflammatory diseases. Gene enrichment analysis suggested that the biological pathways involved in the PMN responses to the iRBCs included insulin receptor, Jak-STAT signaling pathway, mitogen-activated protein kinase (MAPK), and interleukin and interferon-gamma (IFN-γ) signaling pathways. The current study provides fundamental knowledge on the molecular responses of neutrophils to malarial parasites, which may aid in the discovery of novel therapeutic interventions.

The role of HLA-G in parasitic diseases

Little attention has been devoted to the role of HLA-G gene and molecule on parasitic disorders, and the available studies have focused on malaria, African and American trypanosomiasis, leishmaniosis, toxoplasmosis and echinococcosis. After reporting a brief description regarding the role of the cells of innate and adaptive immune system against parasites, we reviewed the major features of the HLA-G gene and molecule and the role of HLA-G on the major cells of immune system. Increased levels of soluble HLA-G (sHLA-G) have been observed in patients presenting toxoplasmosis and in the active phase of echinococcosis. In addition, increased sHLA-G has also been associated with increased susceptibility to malaria and increased susceptibility to develop human African trypanosomiasis (HAT). In contrast, decreased membrane-bound HLA-G has been reported in placenta of patients infected with Plasmodium falciparum and in heart and colon of patients presenting Chagas disease. The 3' untranslated region of the HLA-G gene has been the main focus of studies on malaria, HAT and Chagas disease, exhibiting distinct patterns of associations. Considering that HLA-G is an immune checkpoint molecule, inhibiting the activity of several cells of the immune system, the excessive neoexpression and the increased sHLA-G levels together with the decreased constitutive tissue expression of membrane-bound HLA-G may be detrimental to the host infected with parasite agents.

Promotion of Expansion and Differentiation of Hematopoietic Stem Cells by Interleukin-27 into Myeloid Progenitors to Control Infection in Emergency Myelopoiesis

Emergency myelopoiesis is inflammation-induced hematopoiesis to replenish myeloid cells in the periphery, which is critical to control the infection with pathogens. Previously, pro-inflammatory cytokines such as interferon (IFN)-α and IFN-γ were demonstrated to play a critical role in the expansion of hematopoietic stem cells (HSCs) and myeloid progenitors, leading to production of mature myeloid cells, although their inhibitory effects on hematopoiesis were also reported. Therefore, the molecular mechanism of emergency myelopoiesis during infection remains incompletely understood. Here, we clarify that one of the interleukin (IL)-6/IL-12 family cytokines, IL-27, plays an important role in the emergency myelopoiesis. Among various types of hematopoietic cells in bone marrow, IL-27 predominantly and continuously promoted the expansion of only Lineage⁻Sca-1⁺c-Kit⁺ (LSK) cells, especially long-term repopulating HSCs and myeloid-restricted progenitor cells with long-term repopulating activity, and the differentiation into myeloid progenitors in synergy with stem cell factor. These progenitors expressed myeloid transcription factors such as Spi1, Gfi1, and Cebpa/b through activation of signal transducer and activator of transcription 1 and 3, and had enhanced potential to differentiate into migratory dendritic cells (DCs), neutrophils, and mast cells, and less so into macrophages, and basophils, but not into plasmacytoid DCs, conventional DCs, T cells, and B cells. Among various cytokines, IL-27 in synergy with the stem cell factor had the strongest ability to augment the expansion of LSK cells and their differentiation into myeloid progenitors retaining the LSK phenotype over a long period of time. The experiments using mice deficient for one of IL-27 receptor subunits, WSX-1, and IFN-γ revealed that the blood stage of malaria infection enhanced IL-27 expression through IFN-γ production, and the IL-27 then promoted the expansion of LSK cells, differentiating and mobilizing them into spleen, resulting in enhanced production of neutrophils to control the infection. Thus, IL-27 is one of the limited unique cytokines directly acting on HSCs to promote differentiation into myeloid progenitors during emergency myelopoiesis.

Emergency myelopoiesis is inflammation-induced hematopoiesis that is critical for controlling infection with pathogens, but the molecular mechanism remains incompletely understood. Here, we clarify that one of the interleukin (IL)-6/IL-12 family cytokines, IL-27, plays an important role in emergency myelopoiesis. Among various types of hematopoietic cells in bone marrow, IL-27 predominantly and continuously promoted expansion of only Lineage⁻Sca-1⁺c-Kit⁺ (LSK) cells, especially long-term repopulating hematopoietic stem cells, and differentiation into myeloid progenitors in synergy with stem cell factor. These progenitors expressed myeloid transcription factors such as Spi1, Gfi1, and Cebpa/b through activation of signal transducer and activator of transcription 1 and 3, and had enhanced potential to differentiate into neutrophils, but not into plasmacytoid dendritic cells. Among various cytokines, IL-27 in synergy with stem cell factor had the strongest ability to augment the expansion of LSK cells and their differentiation into myeloid progenitors. The blood stage of malaria infection was revealed to enhance IL-27 expression through interferon-γ production, and IL-27 then promoted the expansion of LSK cells, differentiating and mobilizing them into the spleen, resulting in enhanced production of neutrophils to control the infection. Thus, IL-27 is one of the limited unique cytokines directly acting on hematopoietic stem cells to promote differentiation into myeloid progenitors during emergency myelopoiesis.

Malaria induces anemia through CD8+ T cell-dependent parasite clearance and erythrocyte removal in the spleen

Severe malarial anemia (SMA) in semi-immune individuals eliminates both infected and uninfected erythrocytes and is a frequent fatal complication. It is proportional not to circulating parasitemia but total parasite mass (sequestered) in the organs. Thus, immune responses that clear parasites in organs may trigger changes leading to anemia. Here, we use an outbred-rat model where increasing parasite removal in the spleen escalated uninfected-erythrocyte removal. Splenic parasite clearance was associated with activated CD8(+) T cells, immunodepletion of which prevented parasite clearance. CD8(+) T cell repletion and concomitant reduction of the parasite load was associated with exacerbated (40 to 60%) hemoglobin loss and changes in properties of uninfected erythrocytes. Together, these data suggest that CD8(+) T cell-dependent parasite clearance causes erythrocyte removal in the spleen and thus anemia. In children infected with the human malaria parasite Plasmodium falciparum, elevation of parasite biomass (not the number of circulating parasites) increased the odds ratio for SMA by 3.5-fold (95% confidence intervals [CI95%], 1.8- to 7.5-fold). CD8(+) T cell expansion/activation independently increased the odds ratio by 2.4-fold (CI95%, 1.0- to 5.7-fold). Concomitant increases in both conferred a 7-fold (CI95%, 1.9- to 27.4-fold)-greater risk for SMA. Together, these data suggest that CD8(+)-dependent parasite clearance may predispose individuals to uninfected-erythrocyte loss and SMA, thus informing severe disease diagnosis and strategies for vaccine development.

IMPORTANCE

Malaria is a major global health problem. Severe malaria anemia (SMA) is a complex disease associated with partial immunity. Rapid hemoglobin reductions of 20 to 50% are commonly observed and must be rescued by transfusion (which can carry a risk of HIV acquisition). The causes and risk factors of SMA remain poorly understood. Recent studies suggest that SMA is linked to parasite biomass sequestered in organs. This led us to investigate whether immune mechanisms that clear parasites in organs trigger anemia. In rats, erythropoiesis is largely restricted to the bone marrow, and critical aspects of the spleen expected to be important in anemia are similar to those in humans. Therefore, using a rat model, we show that severe anemia is caused through CD8(+) T cell-dependent parasite clearance and erythrocyte removal in the spleen. CD8 activation may also be a new risk factor for SMA in African children.

Epidemiological and clinical correlates of malaria-helminth co-infections in Southern Ethiopia

Background

In many areas of the world, including Ethiopia, malaria and helminths are co-endemic, therefore, co-infections are common. However, little is known how concurrent infections affect the epidemiology and/or pathogenesis of each other. Therefore, this study was conducted to assess the effects of intestinal helminth infections on the epidemiology and clinical patterns of malaria in southern Ethiopia where both infections are prevalent.

Methods

A cross-sectional study was conducted in 2006 at Wondo Genet Health Center and Bussa Clinic, southern Ethiopia. Consecutive blood film positive malaria patients (N=230) and malaria negative asymptomatic individuals (N=233) were recruited. Malaria parasite detection and quantification was diagnosed using Giemsa-stained thick and thin blood films, respectively. Helminths were detected using direct microscopy and formol-ether concentration techniques. Coarse quantification of helminths ova was made using Kato Katz method.

Results

The over all magnitude of intestinal parasitic infection was high irrespective of malaria infection (67% among malaria positive patients versus 53.1% among malaria non-infected asymptomatic individuals). Trichuris trichiura infection was associated with increased malaria prevalence while increased worm burden of helminths as expressed by egg intensity was associated with increased malaria parasitaemia which could be a potential factor for development of severe malarial infection with the course of the disease. Majority (77%) of the subjects had multiple helminths infection. T. trichiura, Ascaris lumbricoides, Schistosoma mansoni, and hookworm infestation accounted for 64.5, 57.7 %, 28.4%, and 12.2% of the infections, respectively.

Conclusions

Populations in malaria-endemic areas of southern Ethiopia are multi-parasitized with up to four helminths. Mass deworming may be a simple practical approach in endemic areas in reducing the risk of severe malarial attack particularly for those at high risk of both infections.

Gene profiling analysis reveals the contribution of CD24 and P2Y6R to the susceptibility of young rats to Plasmodium berghei infection

Our previous studies have shown that Plasmodium berghei infection induces distinct clinical, parasitological and immunological states in young susceptible rats versus adult resistant rats. This susceptibility was mainly found to be related to inadequate cellular responses. In this study we first identified the altered genes in young susceptible rats. Unexpectedly, transcriptome analysis did not reveal any alteration of effector cytokines or their receptors. At day 13 p.i., six transcripts corresponding to faim3, mesothelin, gas3 (PMP22), gas7, CD24 and P2Y6R were significantly decreased in young infected rats when compared with adult infected rats. Because CD24 and P2Y6R participate in cellular immune responses, we next evaluated their role in the course of infection. Adoptive transfer experiments showed a transient but robust participation of CD24+ cells in the control of parasitaemia. The role of P2Y6R was investigated via its specific ability to be activated by Uridine di-Phosphate (UDP). Young rats treated with UDP partially restored the expression of P2Y6R, controlled parasitaemia and survived thereafter. In conclusion, this study contributes to the discovery of novel biomarkers in young susceptible rats and suggests that the decrease in their expression could be among the reasons for the development of severe pathology in malaria.

The role of protozoa-driven selection in shaping human genetic variability

Protozoa exert a strong selective pressure in humans. The selection signatures left by these pathogens can be exploited to identify genetic modulators of infection susceptibility. We show that protozoa diversity in different geographic locations is a good measure of protozoa-driven selective pressure; protozoa diversity captured selection signatures at known malaria resistance loci and identified several selected single nucleotide polymorphisms in immune and hemolytic anemia genes. A genome-wide search enabled us to identify 5180 variants mapping to 1145 genes that are subjected to protozoa-driven selective pressure. We provide a genome-wide estimate of protozoa-driven selective pressure and identify candidate susceptibility genes for protozoa-borne diseases.

A distinct peripheral blood monocyte phenotype is associated with parasite inhibitory activity in acute uncomplicated Plasmodium falciparum malaria

Monocyte (MO) subpopulations display distinct phenotypes and functions which can drastically change during inflammatory states. We hypothesized that discrete MO subpopulations are induced during malaria infection and associated with anti-parasitic activity. We characterized the phenotype of blood MO from healthy malaria-exposed individuals and that of patients with acute uncomplicated malaria by flow cytometry. In addition, MO defense function was evaluated by an in vitro antibody dependent cellular inhibition (ADCI) assay. At the time of admission, the percentages and absolute numbers of CD16+ MO, and CCR2+CX3CR1+ MO, were high in a majority of patients. Remarkably, expression of CCR2 and CX3CR1 on the CD14(high (hi)) MO subset defined two subgroups of patients that also differed significantly in their functional ability to limit the parasite growth, through the ADCI mechanism. In the group of patients with the highest percentages and absolute numbers of CD14(hi)CCR2+CX3CR1+ MO and the highest mean levels of ADCI activity, blood parasitemias were lower (0.14+/-0.34%) than in the second group (1.30+/-3.34%; p = 0.0053). Data showed that, during a malaria attack, some patients' MO can exert a strong ADCI activity. These results bring new insight into the complex relationships between the phenotype and the functional activity of blood MO from patients and healthy malaria-exposed individuals and suggest discrete MO subpopulations are induced during malaria infection and are associated with anti-parasitic activity.

Marked differences in CRP genotype frequencies between the Fulani and sympatric ethnic groups in Africa

Background

C-reactive protein (CRP) is an acute phase protein that can activate various immune cells and bind to certain Fcγ receptors. The latter may compete with the binding of IgG antibodies to these receptors and could thereby interfere with the antigen-specific immune response. Polymorphisms in the promoter region of the CRP gene have been strongly associated with the plasma concentration of CRP. The known lower susceptibility to malaria in the Fulani ethnic group, as compared to their sympatric neighbours in Africa, has been linked to different genetic backgrounds. The present study was performed to investigate if polymorphisms in the CRP gene could contribute to the lower susceptibility to malaria seen in the Fulani ethnic group.

Methods

The CRP -717 T>C, -286 C>T>A, and +1444 C>T polymorphisms were analysed in asymptomatic Fulani and non-Fulani individuals from Mali and Sudan using Pyrosequencing T and TaqMan r MGB probes.

Results

The rare -286 A allele, previously shown to be associated with increased CRP expression and plasma levels, was shown to be more frequent in the non-Fulani ethnic groups as compared to the sympatric Fulani ethnic group both in Mali and Sudan. The common -717 T allele was more prevalent in the non-Fulani ethnic group compared to the sympatric Fulani ethnic group, but only in Mali. The parasite prevalence was increased for the -286 A allele, but not for the -717 T allele. No differences regarding genotype frequency or parasite prevalence were seen for +1444 C>T.

Conclusion

This study indicate that CRP may play an important role in the immune responses to malaria, and that the -286 C/T/A CRP polymorphism may be a contributing factor to the lower susceptibility to malaria seen in the Fulani.

Injection of lipopolysaccharide induces the migration of splenic neutrophils to the T cell area of the white pulp: role of CD14 and CXC chemokines

There is increasing evidence that neutrophils are involved in the regulation of adaptive immunity. We therefore tested whether these cells may colocalize with T lymphocytes in lymphoid organs. Our results demonstrate that administration of the microbial product LPS induces the migration of neutrophils in the spleen from the red pulp and the marginal zone to the area of the white pulp where T cells reside. This movement is CD14-dependent, whereas the recruitment of neutrophils in the peritoneal cavity is increased in the absence of CD14. Our data further suggest the involvement of the chemokine MIP-2 and keratinocyte-derived chemokine and their receptor CXCR2. We conclude that neutrophils may interact with naïve T cells upon infection/inflammation and that the migration of neutrophils in the lymphoid organs and in the periphery is regulated differently by a signal transduced by CD14.