Immunoregulation /Immune Recognition In Filarial/Nonfilarial Parasitic Infection

National Institute Of Allergy And Infectious Diseases

Investigators

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Abstract

The overriding goal of this project is to provide an understanding of how the immunologic responses to filarial and related parasites are controlled. The major aspects of this project involve the parasite-specific responses in lymphatic filariasis (LF), loiasis, onchocerciasis and most recently strongyloidiasis in terms of regulation, pathogenesis protective immunity, and the genetic underpinnings of these host responses. The major objectives are to identify the mechanisms by which the modulation/regulation of immune responsiveness works in filarial and related parasitic infections; 2) to identify factors involved in the pathogenesis of disease in filarial infections; 3) to identify the role of host and parasite factors underlying the differential responsiveness to parasite antigens and the subsequent clinical and immunologic outcome; and 4) to understand the immunologic correlates of immunity in human filarial infection. The hallmark of the T cell response seen in individuals with patent systemic helminth infections (e.g. the filariae or S. stercoralis) is a profound inability to proliferate or produce cytokines associated with a Type-1 response (IL-2 and IFN-) and Type-17 (IL-17) in response to parasite antigen. This parasite-specific anergy is mediated, in large part, by IL-10. Other members of the IL-10 superfamily (IL-19 and IL-24) have been now shown to be upregulated in patent filarial infection and in strongyloidiasis (a process driven by IL-10 itself and IL-37). Because IL-10 is the primary cytokine driving the modulation of the host response in filarial infections. We performed binding assays with Brugia malayi antigen extracts and human IL-10R1. Bm5539 was the top binding hit. We identified a short sequence, termed truncated Bm5339, that has structural similarities to the human IL-10 functional dimer. Sequence comparisons revealed that other filarial parasites possess Bm5539 orthologues. Using recombinant Bm5539 in a modified Luciferase Immunoprecipitation System assay, we confirmed that both the truncated and full-length forms of the protein can bind to human IL-10R1. Truncated Bm5539 could inhibit human IL-10-driven phosphorylation of STAT3 thereby demonstrating that Bm5539 acts as an IL-10 antagonist most likely through competitive binding to the receptor. We provide a structural basis for these observations using computational modeling and simulations. Not only have chronic helminth infections been shown to modulate T cell responses, but it has also been shown to result in profound monocyte (and dendritic cell DC) dysfunction that can be reversed by effective anthelmintic treatment. We have explored the mechanisms by which parasite products alter the function of human APCs (both monocytes and DC). Using global protein expression profiling comparisons between microfilariae (mf)-exposed or mfunexposed human DCs, we have been able to show that parasite-derived products from mf significantly downregulated mTOR and the downstream molecules eIF2, eIF4 and p70S6K. The inhibition of mTOR occurs within minutes of parasite exposure and leads to autophagy and the induction of IDO. To explore more fully how the parasites drive this mTOR inhibition, we have identified the cargo (miRNA/proteins) contained within the extracellular vesicles (EVs) of mf, then demonstrated that they are internalized rapidly by APCs, and finally demonstrated their ability to downregulate the phosphorylation of mTOR. Because chronic filarial (and other helminth) infections may alter immune reactivity to other (non-parasite) antigens and because these alterations may have profound implications for the clinical outcome of these non-filarial infections, collaborative studies in India and Mali have shown that the presence of active filarial infection and/or chronic intestinal helminth infection very clearly blunts the Type 1 (and Th17) response to non-filarial antigens in the context of co-infection. Over the past year, we have focused on the influence of pre-existing helminth infections on cutaneous leishmaniasis (in Mali). By comparing monocytes of individuals who were not exposed to sand fly bites (mainly North American controls) and those from Mali with filarial and leishmanial co-infection, we found that IL-6 and CCL4; cytokines were driven by sandfly glycoproteins in both groups.Furthermore, infection with filarial parasites resulted in upregulation of CCL22, a type-2 associated chemokine, both at the mRNA levels and by its observed effect on the frequency of recruited monocytes. How helminth infection alters the microbiome at the intestinal mucosal surfaces has been an important line of research as well. We performed a systematic review and metaanalysis (from all original datasets) to understand the conflicting data generated in the past few years. A predefined minimally biased search strategy identified 23 studies in humans. For each of these studies, we qualitatively addressed the effects of helminth infection on within-individual (alpha) and between-individual (beta) fecal microbiome diversity, infection-associated microbial taxa, the effect of helminth clearance on microbiome composition, microbiome composition as a predictor of infection status or treatment outcome, and treatment-specific effects on the fecal microbiome. Concomitantly, we performed a meta-analysis on a subset of 7 of these studies containing raw, paired-end 16S reads and individual-level metadata, comprising 424 pretreatment or untreated HI individuals and 497 HU controls. After reducing the batch effect and adjusting for age, our data demonstrated that intestinal helminth parasites can alter the host gut microbiome by increasing alpha diversity and promoting taxonomic reassortment and gradient collapse. Most strongly influencing the microbiome composition were the helminths found in the large intestine, Enterobius vermicularis and Trichuris trichiura, suggesting that this influence appears to be specific to soil-transmitted helminths (STH) species and host anatomical niche. In summary, using a large and diverse sample set captured in the meta-analysis, we were able to evaluate the influence of individual helminth species as well as species-species interactions, each of which explained a significant portion of the variation in the microbiome.