Polymorphisms in the RNASE3 gene are associated with susceptibility to cerebral malaria in Ghanaian children

Human blood neutrophils generate ROS through FcγR-signaling to mediate protection against febrile P. falciparum malaria

Blood phagocytes, such as neutrophils and monocytes, generate reactive oxygen species (ROS) as a part of host defense response against infections. We investigated the mechanism of Fcγ-Receptor (FcγR) mediated ROS production in these cells to understand how they contribute to anti-malarial immunity. Plasmodium falciparum merozoites opsonized with naturally occurring IgG triggered both intracellular and extracellular ROS generation in blood phagocytes, with neutrophils being the main contributors. Using specific inhibitors, we show that both FcγRIIIB and FcγRIIA acted synergistically to induce ROS production in neutrophils, and that NADPH oxidase 2 and the PI3K intracellular signal transduction pathway were involved in this process. High levels of neutrophil ROS were also associated with protection against febrile malaria in two geographically diverse malaria endemic regions from Ghana and India, stressing the importance of the cooperation between anti-malarial IgG and neutrophils in triggering ROS-mediated parasite killing as a mechanism for naturally acquired immunity against malaria.

Eosinophils Suppress the Migration of T Cells Into the Brain of Plasmodium berghei-Infected Ifnar1-/- Mice and Protect Them From Experimental Cerebral Malaria

Cerebral malaria is a potentially lethal disease, which is caused by excessive inflammatory responses to Plasmodium parasites. Here we use a newly developed transgenic Plasmodium berghei ANKA (PbA_Ama1OVA) parasite that can be used to study parasite-specific T cell responses. Our present study demonstrates that Ifnar1^-/- mice, which lack type I interferon receptor-dependent signaling, are protected from experimental cerebral malaria (ECM) when infected with this novel parasite. Although CD8⁺ T cell responses generated in the spleen are essential for the development of ECM, we measured comparable parasite-specific cytotoxic T cell responses in ECM-protected Ifnar1^-/- mice and wild type mice suffering from ECM. Importantly, CD8⁺ T cells were increased in the spleens of ECM-protected Ifnar1^-/- mice and the blood-brain-barrier remained intact. This was associated with elevated splenic levels of CCL5, a T cell and eosinophil chemotactic chemokine, which was mainly produced by eosinophils, and an increase in eosinophil numbers. Depletion of eosinophils enhanced CD8⁺ T cell infiltration into the brain and increased ECM induction in PbA_Ama1OVA-infected Ifnar1^-/- mice. However, eosinophil-depletion did not reduce the CD8⁺ T cell population in the spleen or reduce splenic CCL5 concentrations. Our study demonstrates that eosinophils impact CD8⁺ T cell migration and proliferation during PbA_Ama1OVA-infection in Ifnar1^-/- mice and thereby are contributing to the protection from ECM.

Emerging Evidence for Pleiotropism of Eosinophils

Eosinophils are complex granulocytes with the capacity to react upon diverse stimuli due to their numerous and variable surface receptors, which allows them to respond in very different manners. Traditionally believed to be only part of parasitic and allergic/asthmatic immune responses, as scientific studies arise, the paradigm about these cells is continuously changing, adding layers of complexity to their roles in homeostasis and disease. Developing principally in the bone marrow by the action of IL-5 and granulocyte macrophage colony-stimulating factor GM-CSF, eosinophils migrate from the blood to very different organs, performing multiple functions in tissue homeostasis as in the gastrointestinal tract, thymus, uterus, mammary glands, liver, and skeletal muscle. In organs such as the lungs and gastrointestinal tract, eosinophils are able to act as immune regulatory cells and also to perform direct actions against parasites, and bacteria, where novel mechanisms of immune defense as extracellular DNA traps are key factors. Besides, eosinophils, are of importance in an effective response against viral pathogens by their nuclease enzymatic activity and have been lately described as involved in severe acute respiratory syndrome coronavirus SARS-CoV-2 immunity. The pleiotropic role of eosinophils is sustained because eosinophils can be also detrimental to human physiology, for example, in diseases like allergies, asthma, and eosinophilic esophagitis, where exosomes can be significant pathophysiologic units. These eosinophilic pathologies, require specific treatments by eosinophils control, such as new monoclonal antibodies like mepolizumab, reslizumab, and benralizumab. In this review, we describe the roles of eosinophils as effectors and regulatory cells and their involvement in pathological disorders and treatment.

Human RNase3 immune modulation by catalytic-dependent and independent modes in a macrophage-cell line infection model

The human RNase3 is a member of the RNaseA superfamily involved in host immunity. RNase3 is expressed by leukocytes and shows broad-spectrum antimicrobial activity. Together with a direct antimicrobial action, RNase3 exhibits immunomodulatory properties. Here, we have analysed the transcriptome of macrophages exposed to the wild-type protein and a catalytic-defective mutant (RNase3-H15A). The analysis of differently expressed genes (DEGs) in treated THP1-derived macrophages highlighted a common pro-inflammatory "core-response" independent of the protein ribonucleolytic activity. Network analysis identified the epidermal growth factor receptor (EGFR) as the main central regulatory protein. Expression of selected DEGs and MAPK phosphorylation were inhibited by an anti-EGFR antibody. Structural analysis suggested that RNase3 activates the EGFR pathway by direct interaction with the receptor. Besides, we identified a subset of DEGs related to the protein ribonucleolytic activity, characteristic of virus infection response. Transcriptome analysis revealed an early pro-inflammatory response, not associated to the protein catalytic activity, followed by a late activation in a ribonucleolytic-dependent manner. Next, we demonstrated that overexpression of macrophage endogenous RNase3 protects the cells against infection by Mycobacterium aurum and the human respiratory syncytial virus. Comparison of cell infection profiles in the presence of Erlotinib, an EGFR inhibitor, revealed that the receptor activation is required for the antibacterial but not for the antiviral protein action. Moreover, the DEGs related and unrelated to the protein catalytic activity are associated to the immune response to bacterial and viral infection, respectively. We conclude that RNase3 modulates the macrophage defence against infection in both catalytic-dependent and independent manners.

Haplotype of RNASE 3 polymorphisms is associated with severe malaria in an Indian population

Severe malaria (SM) caused by Plasmodium falciparum (Pf) infection has been associated with life-threatening anemia, metabolic acidosis, cerebral malaria and multiorgan dysfunction. It may lead to death if not treated promptly. RNASE 3 has been linked to Pf growth inhibition and its polymorphisms found associated with SM and cerebral malaria in African populations. This study aimed to assess the association of RNASE 3 polymorphisms with SM in an Indian population. RNASE 3 gene and flanking regions were amplified followed by direct DNA sequencing in 151 Indian patients who visited Wenlock District Government Hospital, Mangalore, Karnataka, India. Allele, genotype and haplotype frequencies were compared between patients with SM (n = 47) and uncomplicated malaria (UM; n = 104). Homozygous mutant genotype was only found for rs2233860 (+ 499G > C) polymorphism (< 1% frequency). No significant genetic associations were found for RNASE 3 polymorphism genotypes and alleles in Indian SM patients using the Fisher's exact test. C-G-G haplotype of rs2233859 (− 38C > A), rs2073342 (+ 371C > G) and rs2233860 (+ 499G > C) polymorphisms was correlated significantly with SM patients (OR = 3.03; p = 0.008) after Bonferroni correction. A haplotype of RNASE 3 gene was found associated with an increased risk of SM and confirming that RNASE 3 gene plays a role in susceptibility to SM.

Immune Modulation by Human Secreted RNases at the Extracellular Space

The ribonuclease A superfamily is a vertebrate-specific family of proteins that encompasses eight functional members in humans. The proteins are secreted by diverse innate immune cells, from blood cells to epithelial cells and their levels in our body fluids correlate with infection and inflammation processes. Recent studies ascribe a prominent role to secretory RNases in the extracellular space. Extracellular RNases endowed with immuno-modulatory and antimicrobial properties can participate in a wide variety of host defense tasks, from performing cellular housekeeping to maintaining body fluid sterility. Their expression and secretion are induced in response to a variety of injury stimuli. The secreted proteins can target damaged cells and facilitate their removal from the focus of infection or inflammation. Following tissue damage, RNases can participate in clearing RNA from cellular debris or work as signaling molecules to regulate the host response and contribute to tissue remodeling and repair. We provide here an overall perspective on the current knowledge of human RNases’ biological properties and their role in health and disease. The review also includes a brief description of other vertebrate family members and unrelated extracellular RNases that share common mechanisms of action. A better knowledge of RNase mechanism of actions and an understanding of their physiological roles should facilitate the development of novel therapeutics.

Genetic variants of RNASE3 (ECP) and susceptibility to severe malaria in Senegalese population

Background

Severe forms of malaria (SM) are an outcome of Plasmodium falciparum infection and can cause death especially in children under 4 years of age. RNASE3 (ECP) has been identified as an inhibitor of Plasmodium parasites growth in vitro, and genetic analysis in hospitalized Ghanaian subjects has revealed the RNASE3 +371G/C (rs2073342) polymorphism as a susceptibility factor for cerebral malaria. The +371 C allele results in an Arg/Thr mutation that abolishes the cytotoxic activity of the ECP protein. The present study aims to investigate RNASE3 gene polymorphisms and their putative link to severe malaria in a malaria cohort from Senegal.

Methods/results

Patients enrolled from hospitals were classified as having either uncomplicated (UM) or severe malaria (SM). The analysis of the RNASE3 gene polymorphisms was performed in 241 subjects: 178 falciparum infected (96 SM, 82 UM) and 63 non-infected subjects as population control group (CTR). Six frequent SNPs (MAF > 3%) were identified, and one SNP was associated with malaria severity by performing a logistic regression analysis SM vs.UM: RNASE3 +499G/C (rs2233860) under age, sex as covariates and HbS/HbC polymorphisms adjustment (p = 0.003, OR 0.43, CI 95% 0.20–0.92). The polymorphisms: +371G/C (rs2073342), +499G/C (rs2233860) and +577A/T (rs8019343) defined a haplotype risk (G-G-T) for malaria severity (Fisher exact test, p = 0.03) (OR 4.1, IC 95% (1.1–14.9).

Conclusion

In addition to the previously described association of +371G/C polymorphism in Ghanaians cohort, the RNASE3 +499G/C polymorphism was associated with susceptibility to SM in a Senegalese population. The haplotype +371G/+499G/+577T defined by RNASE3 polymorphisms was associated with severity. The genetic association identified independently in the Senegalese population provide additional evidence of a role of RNASE3 (ECP) in malaria severity.

Rapid Evolution of Primate Type 2 Immune Response Factors Linked to Asthma Susceptibility

Host immunity pathways evolve rapidly in response to antagonism by pathogens. Microbial infections can also trigger excessive inflammation that contributes to diverse autoimmune disorders including asthma, lupus, diabetes, and arthritis. Definitive links between immune system evolution and human autoimmune disease remain unclear. Here we provide evidence that several components of the type 2 immune response pathway have been subject to recurrent positive selection in the primate lineage. Notably, substitutions in the central immune regulator IL13 correspond to a polymorphism linked to asthma susceptibility in humans. We also find evidence of accelerated amino acid substitutions as well as gene gain and loss events among eosinophil granule proteins, which act as toxic antimicrobial effectors that promote asthma pathology by damaging airway tissues. These results support the hypothesis that evolutionary conflicts with pathogens promote tradeoffs for increasingly robust immune responses during animal evolution. Our findings are also consistent with the view that natural selection has contributed to the spread of autoimmune disease alleles in humans.

Overview of human genetic susceptibility to malaria: From parasitemia control to severe disease

Malaria is a life-threatening blood disease caused by the protozoan Plasmodium. Infection may lead to several different patterns of symptoms in the host: asymptomatic state, uncomplicated disease or severe disease. Severe malaria occurs mostly in young children and is a major cause of death. Disease is thought to result from the sequestration of parasites in the small blood vessels of the brain and the deregulation of key immune system elements. The cellular and molecular regulatory mechanisms underlying the pathogenesis of disease are however not fully understood. What is known it is that the genetic determinants of the host play an important role in the severity of the disease and the outcome of infection. Here we review the most convincing results obtained through genetic epidemiology studies concerning the genetic control of malaria in human caused by Plasmodium falciparum infection. The identification of genes conferring susceptibility or resistance to malaria might improve diagnosis and treatment.

The Ribonuclease A Superfamily in Humans: Canonical RNases as the Buttress of Innate Immunity

In humans, the ribonuclease A (RNase A) superfamily contains eight different members that have RNase activities, and all of these members are encoded on chromosome 14. The proteins are secreted by a large variety of different tissues and cells; however, a comprehensive understanding of these proteins’ physiological roles is lacking. Different biological effects can be attributed to each protein, including antiviral, antibacterial and antifungal activities as well as cytotoxic effects against host cells and parasites. Different immunomodulatory effects have also been demonstrated. This review summarizes the available data on the human RNase A superfamily and illustrates the significant role of the eight canonical RNases in inflammation and the host defence system against infections.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CXCL10 gene promoter polymorphism -1447A>G correlates with plasma CXCL10 levels and is associated with male susceptibility to cerebral malaria

The risk factors for cerebral malaria (CM) and the wide variation in clinical manifestations of malaria are poorly understood. Recent studies indicate that interferon gamma inducible chemokine, CXCL10, is a strong predictor of both human and experimental cerebral malaria. Increased plasma and cerebrospinal fluid levels of CXCL10 were tightly associated with fatal CM in Indian and Ghanaian patients. In the present study, we hypothesized that in a subset of malaria patients, CM susceptibility is associated with variation in CXCL10 expression. We determined whether polymorphisms in the CXCL10 gene promoter region played a role in the clinical status of malaria patients and addressed the genetic basis of CXCL10 expression during malaria infection. Following extensive bioinformatics analyses, two reported single nucleotide polymorphisms in the CXCL10 promoter (-135G>A [rs56061981] and -1447A>G [rs4508917]) were identified among 66 CM and 69 non-CM Indian patients using PCR-restriction fragment length polymorphism assay. Individuals with the -1447(A/G) genotype were susceptible to CM (adjusted odds ratio [AOR] = 2.60, 95% CI = 1.51-5.85, p = 0.021). In addition, individuals with the -1447(A/G) genotype had significantly higher plasma CXCL10 levels than individuals with the -1447(A/A) genotype. Stratifying patients according to gender, the observed association of CM with over expression of CXCL10 were more pronounced in males than in female patients (AOR = 5.47, 95% CI = 1.34-22.29, p = 0.018). Furthermore, -135G>A polymorphism conferred a decreased risk of CM among males (AOR = 0.19, 95% CI = 0.05-0.78, p = 0.021). Polymorphisms in the CXCL10 gene promoter sequence were associated with increased CXCL10 production, which is linked to severity of CM. These results suggest that the -1447A>G polymorphism in CXCL10 gene promoter could be partly responsible for the reported variation underlying severity of CM outcomes particularly in males.

Eosinophils: changing perspectives in health and disease

Eosinophils have been traditionally perceived as terminally differentiated cytotoxic effector cells. Recent studies have profoundly altered this simplistic view of eosinophils and their function. New insights into the molecular pathways that control the development, trafficking and degranulation of eosinophils have improved our understanding of the immunomodulatory functions of these cells and their roles in promoting homeostasis. Likewise, recent developments have generated a more sophisticated view of how eosinophils contribute to the pathogenesis of different diseases, including asthma and primary hypereosinophilic syndromes, and have also provided us with a more complete appreciation of the activities of these cells during parasitic infection.

Eosinophils: changing perspectives in health and disease

Eosinophils have been traditionally perceived as terminally differentiated cytotoxic effector cells. Recent studies have profoundly altered this simplistic view of eosinophils and their function. New insights into the molecular pathways that control the development, trafficking and degranulation of eosinophils have improved our understanding of the immunomodulatory functions of these cells and their roles in promoting homeostasis. Likewise, recent developments have generated a more sophisticated view of how eosinophils contribute to the pathogenesis of different diseases, including asthma and primary hypereosinophilic syndromes, and have also provided us with a more complete appreciation of the activities of these cells during parasitic infection.

Fc γ receptor IIIB (FcγRIIIB) polymorphisms are associated with clinical malaria in Ghanaian children

Plasmodium falciparum malaria kills nearly a million people annually. Over 90% of these deaths occur in children under five years of age in sub-Saharan Africa. A neutrophil mediated mechanism, the antibody dependent respiratory burst (ADRB), was recently shown to correlate with protection from clinical malaria. Human neutrophils constitutively express Fc gamma receptor-FcγRIIA and FcγRIIIB by which they interact with immunoglobulin (Ig) G (IgG)-subclass antibodies. Polymorphisms in exon 4 of FCGR2A and exon 3 of FCGR3B genes encoding FcγRIIA and FcγRIIIB respectively have been described to alter the affinities of both receptors for IgG. Here, associations between specific polymorphisms, encoding FcγRIIA p.H166R and FcγRIIIB-NA1/NA2/SH variants with clinical malaria were investigated in a longitudinal malaria cohort study. FcγRIIA-p.166H/R was genotyped by gene specific polymerase chain reaction followed by allele specific restriction enzyme digestion. FCGR3B-exon 3 was sequenced in 585 children, aged 1 to 12 years living in a malaria endemic region of Ghana. Multivariate logistic regression analysis found no association between FcγRIIA-166H/R polymorphism and clinical malaria. The A-allele of FCGR3B-c.233C>A (rs5030738) was significantly associated with protection from clinical malaria under two out of three genetic models (additive: p=0.0061; recessive: p=0.097; dominant: p=0.0076) of inheritance. The FcγRIIIB-SH allotype (CTGAAA) containing the 233A-allele (in bold) was associated with protection from malaria (p=0.049). The FcγRIIIB-NA2*03 allotype (CTGCGA), a variant of the classical FcγRIIIB-NA2 (CTGCAA) was associated with susceptibility to clinical malaria (p=0.0092). The present study is the first to report an association between a variant of FcγRIIIB-NA2 and susceptibility to clinical malaria and provides justification for further functional characterization of variants of the classical FcγRIIIB allotypes. This would be crucial to the improvement of neutrophil mediated functional assays such as the ADRB assay aimed at assessing the functionality of antibodies induced by candidate malaria vaccines.

Eosinophil cationic protein: overview of biological and genetic features

The eosinophil cationic protein (ECP) is a small polypeptide that originates from activated eosinophil granulocytes. A wide range of stimuli has been shown to induce the secretion of ECP. The gene that encodes the human ECP is located on chromosome 14, and the protein shares the overall three-dimensional structure and the RNase active-site residues with other proteins in the RNase A superfamily. Several single-nucleotide polymorphisms in the human ECP gene have been currently described. ECP has many biological functions, including an immunoregulatory function, the regulation of fibroblast activity, and the induction of mucus secretion in the airway. Additionally, the protein is a potent cytotoxic molecule and has the capacity to kill mammalian and nonmammalian cells. The purpose of this article was to review the known biological and genetic characteristics of ECP that contribute to the understanding of this protein's role in the development and progression of a wide variety of diseases.