Immune System Investigation Using Parasitic Helminths

Coevolutionary adaptation between humans and helminths has developed a finely tuned balance between host immunity and chronic parasitism due to immunoregulation. Given that these reciprocal forces drive selection, experimental models of helminth infection are ideally suited for discovering how host protective immune responses adapt to the unique tissue niches inhabited by these large metazoan parasites. This review highlights the key discoveries in the immunology of helminth infection made over the last decade, from innate lymphoid cells to the emerging importance of neuroimmune connections. A particular emphasis is placed on the emerging areas within helminth immunology where the most growth is possible, including the advent of genetic manipulation of parasites to study immunology and the use of engineered T cells for therapeutic options. Lastly,we cover the status of human challenge trials with helminths as treatment for autoimmune disease, which taken together, stand to keep the study of parasitic worms at the forefront of immunology for years to come.

Spatial and Temporal Mapping of Human Innate Lymphoid Cells Reveals Elements of Tissue Specificity

Innate lymphoid cells (ILC) play critical roles in regulating immunity, inflammation, and tissue homeostasis in mice. However, limited access to non-diseased human tissues has hindered efforts to profile anatomically-distinct ILCs in humans. Through flow cytometric and transcriptional analyses of lymphoid, mucosal, and metabolic tissues from previously healthy human organ donors, here we have provided a map of human ILC heterogeneity across multiple anatomical sites. In contrast to mice, human ILCs are less strictly compartmentalized and tissue localization selectively impacts ILC distribution in a subset-dependent manner. Tissue-specific distinctions are particularly apparent for ILC1 populations, whose distribution was markedly altered in obesity or aging. Furthermore, the degree of ILC1 population heterogeneity differed substantially in lymphoid versus mucosal sites. Together, these analyses comprise a comprehensive characterization of the spatial and temporal dynamics regulating the anatomical distribution, subset heterogeneity, and functional potential of ILCs in non-diseased human tissues.

The prostaglandin D2 receptor chemoattractant receptor homologous molecule expressed on Th2 cells regulates accumulation of group 2 innate lymphoid cells in the inflamed lung (IRC7P.426)

Group 2 innate lymphoid cells (ILC2s) promote type 2 immunity and inflammation, but the pathways that control ILC2 migration into inflamed tissues remain poorly understood. Here, we show that the prostaglandin D2 (PGD2) receptor chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2) regulates ILC2 accumulation in the lung in vivo. The frequency of ILC2s that expressed CRTH2 was significantly higher in healthy human and murine peripheral blood than in the lung, suggesting that regulation of CRTH2 expression might be associated with ILC2 accumulation in the lung. Consistent with this, CRTH2-expressing murine ILC2s accumulated in the lung in response to PGD2. Further, CRTH2-deficient mice exhibited reduced ILC2 accumulation and helminth-induced type 2 inflammation in the lung compared to wild-type mice. Critically, adoptive transfer of CRTH2-sufficient ILC2s restored helminth-induced pulmonary inflammation in CRTH2-deficient mice. Together, these data suggest that the PGD2-CRTH2 pathway regulates ILC2 accumulation and type 2 inflammation in the lung in vivo.

Thymic stromal lymphopoietin-mediated extramedullary hematopoiesis promotes allergic inflammation (INC5P.328)

Extramedullary hematopoiesis (EMH) refers to the differentiation of hematopoietic stem cells (HSCs) into effector cells that occurs in compartments outside of the bone marrow. Previous studies linked pattern recognition receptor (PRR)-expressing HSCs, EMH and immune responses to microbial stimuli. However, whether EMH operates in broader immune contexts remains unknown. Here, we demonstrate a previously unrecognized role for thymic stromal lymphopoietin (TSLP) in promoting the population expansion of progenitor cells in the periphery and identify that TSLP-elicited progenitors differentiated into effector cells including macrophages and granulocytes; and that these cells selectively contributed to type 2 cytokine responses. The frequency of circulating progenitor cells was also increased in allergic patients with a gain-of-function polymorphism in TSLP, suggesting the TSLP-EMH pathway may operate in human disease. These data demonstrate that TSLP-induced EMH contributes to the development of Th2 cytokine-mediated inflammation and indicate that EMH is a conserved mechanism of innate immunity.

Dissecting mechanisms underlying the pathogenesis of eosinophilic esophagitis (HYP6P.263)

Eosinophilic esophagitis (EoE) is an allergic disease characterized by esophageal eosinophilia, inflammation, and dysfunction. EoE has become increasingly common, but current management strategies are nonspecific. Thus, there is an urgent need to identify new pathways that could be targeted to treat EoE. Recently, EoE was associated with a gain-of-function polymorphism in the gene that encodes thymic stromal lymphopoietin (TSLP), a cytokine that promotes allergic inflammation and peripheral basophilia. However, how TSLP and basophils might contribute to the development of eosinophil responses during EoE remains unknown. Here, we employed a new murine model of EoE-like disease to investigate the role of TSLP and basophils in promoting esophageal eosinophil responses. Development of esophageal eosinophil responses was dependent on TSLP-elicited basophils, and antibody-mediated neutralization of TSLP or depletion of basophils ameliorated established esophageal eosinophilia. In addition, we examined how sort-purified human basophils influence eosinophil responses in vitro. Finally, elevated TSLP levels and exaggerated basophil responses observed in esophageal biopsies from EoE patients correlated with eosinophil responses. Together, these data indicate that TSLP-elicited basophil responses may play a key role in mediating eosinophil responses in EoE, suggesting that the TSLP-basophil axis could represent a new and promising therapeutic target to treat this disease.

Innate lymphoid cells promote airway epithelial repair through the amphiregulin-EGFR pathway (P3250)

Innate lymphoid cells (ILCs) are a recently described group of immune cells that regulate immunity and inflammation at barrier surfaces. While recent studies have implicated Group 2 ILCs as initiators of pathologic Type 2 airway inflammation, the tissue-protective roles of ILCs in the respiratory tract remain poorly understood. Using genome-wide transcriptional profiling, we identify that naïve lung-resident group 2 ILCs express multiple genes associated with tissue repair pathways, including the epidermal growth factor family member amphiregulin. Amphiregulin was increased in a model of influenza virus-induced lung injury and ILC depletion during infection resulted in decreased amphiregulin expression, reduced lung function and impaired airway remodeling. IL-33 promoted expression of amphiregulin in lung ILCs and administration of amphiregulin effectively restored airway tissue remodeling in ILC-depleted mice, suggesting that ILC-intrinsic amphiregulin is a central mediator of epithelial repair. Supporting this, chemical or genetic inhibition of the EGFR-amphiregulin pathway resulted in severely impaired lung function and a failure to restore airway tissue homeostasis, leading to increased host mortality. Taken together, these data indicate a critical role for group 2 ILCs in mediating lung tissue homeostasis though an IL-33-amphiregulin-EGFR axis and suggest that ILCs serve as a key link between the signaling pathways of Type 2 inflammation and tissue repair.

TSLP-mediated extramedullary hematopoiesis promotes allergic inflammation (P4473)

Extramedullary hematopoiesis (EMH) refers to the differentiation of hematopoietic stem cells (HSCs) into effector cells that occurs in compartments outside of the bone marrow. Previous studies established a link between pattern recognition receptor-expressing HSCs, EMH and innate immune responses to bacterial or viral pathogens. However, the factors that regulate EMH and whether EMH is a conserved mechanism of innate immunity to diverse stimuli remain poorly defined. Here, we demonstrate a previously unrecognized role for thymic stromal lymphopoietin (TSLP) in promoting the population expansion of Lineage-, CD34+, c-Kit+ granulocyte-monocyte progenitor (GMP)-like cells in the periphery. TSLP-elicited progenitors possess the capacity to differentiate into macrophages, mast cells and basophils. Critically, adoptive transfer of TSLP-elicited GMP-like cells was sufficient to promote Th2 cytokine-dependent immunity to an intestinal helminth parasite, demonstrating a role for TSLP-elicited GMP-like cells in promoting inflammation. Further, circulating progenitor cells were also increased in allergic patients with a gain-of-function polymorphism in TSLP, suggesting that the TSLP-EMH pathway may be operational in human disease. These data demonstrate a previously unrecognized role for TSLP in promoting EMH that contributes to the development of Th2-cytokine-mediated inflammation and identify the TSLP-EMH pathway as a possible therapeutic target to treat allergic inflammation.