The immunomodulatory capacity of helminths on inflammation: Impact of eosinophils on <em>E. coli</em>-induced sepsis and genome-wide transcriptome profiling of human monocytes stimulated with helminth extract and LPS implicate immune functions and diseases

Abstract

Human filarial nematode infections cause lymphatic filariasis and onchocerciasis in more than 150 million people worldwide. An infection can result in debilitating clinical manifestations like visual impairment or lymphedema that lead to socioeconomic problems and is therefore listed by the World Health Organization for elimination. Principally, filariae modulate cellular immune responses for long-term survival in their host and this modulation of the host’s immune response also dictates the occurrence of host pathology. Helminth infections and helminth-derived products can furthermore modify host immune responses to protect against inflammatory and autoimmune diseases. For instance, we previously provided evidence that infection with the rodent filarial nematode Litomosoides sigmodontis, a well-accepted model to study immune responses during filariasis, improves sepsis outcome without worsen immune paralysis and protects against autoimmune and type 2 diabetes. <br /> Since eosinophil granulocytes are a hallmark of helminth infections we examined the impact of murine eosinophils against <em>Escherichia coli</em>-induced sepsis and the effect of the specific chemoattractants eotaxin-1 and 2 (CCL11 and CCL24) on the release of sepsis-relevant cytokines and chemokines of bone-marrow-derived eosinophils (bmEos). We identified eotaxin-2 (CCL24) to modify the interleukin (IL)-4 response after LPS, P3C and L. sigmodontis crude extract stimulation and to alter the expression of the eotaxin receptor C-C chemokine receptor type 3 (CCR3). The intercellular adhesion molecule 1 (ICAM-1) was not affected by CCL24 treatment. In vivo relevance of eosinophils during the course of a bacterial sepsis was demonstrated using eosinophil-deficient ΔdblGATA mice. Those mice had an exacerbated sepsis outcome with increased pro-inflammatory IL-6 and CXCL2 levels, worsened hypothermia and reduced numbers of adaptive and innate immune cells six hours after <em>E. coli </em>challenge compared to wildtype controls. Co-cultivation of bmEos and <em>E. coli</em> highlighted the potential to reduce of the bacterial burden in vitro via the formation of NET-like extracellular structures and phagocytosis. Initial results of a transcriptome-wide analysis of sorted SiglecF+ eosinophils revealed a L. sigmodontis-dependent but <em>E. coli</em>-independent effect on eosinophil modulation. <br /> We furthermore investigated the immunomodulatory effect of the crude extract of the human pathogenic filaria Brugia malayi (BmA) on the transcriptome of purified human CD14+ monocytes derived from twenty healthy male European non-endemic volunteers. Based on a genome-wide transcriptional profiling more than 47.000 transcripts of monocytes stimulated with BmA, <em>E. coli</em> lipopolysaccharide ultrapure (LPS) or a successive stimulation of both were analyzed. Several genes were identified that were differentially expressed upon BmA priming before LPS re-stimulation including genes like PTX3↓, MMP9↑, CXCL5/ENA-78↑, CXCL6/GCP-2↑, CXCL7/PPBP↑, and CCL20/MIP3α↓. Quantification of CXCL5 and CXCL6 protein levels confirmed our results. Lower expression levels of HLA-DR and CD86 on BmA primed monocytes were further detected by flow cytometry. BmA-only stimulation reduced the frequency of apoptotic cells whereas pre-stimulation did not alter apoptosis after LPS stimulation. Accordingly, Ingenuity Pathway Analysis (IPA) © of the transcriptome of monocyte LPS responses in dependence on BmA-priming depicted associations in immune functions and inflammatory disorders like granulocyte and agranulocyte adhesion, diapedesis and atherosclerosis. Notably, BmA treatment affected several IL-17-dependent pathways like signaling in psoriasis, arthritis and allergic inflammatory airway diseases.<br /> Thus, exposure of human monocytes and murine eosinophils to filarial extracts modifies inflammatory immune responses and affects the response to subsequent stimuli. This immunomodulation may not only impact the development of filaria-caused pathology in humans, but may also affect bystander immune responses that contribute to dysregulated immune responses as they occur during autoimmunity or inflammation during sepsis. Since earlier results indicate that specific gene variants are associated with the severity of pathology, genome-wide analysis of expression quantitative trait loci (e²QTL) will further point out regulatory gene variants that are correlated with differential expressed transcripts and may reveal new targets for treatment strategies against lymphatic filariasis and dysregulated immune responses.