In Situ Maturation and Tissue Adaptation of Type 2 Innate Lymphoid Cell Progenitors.

Innate lymphoid cells (ILCs) are generated early during ontogeny and persist predominantly as tissue-resident cells. Here, we examined how ILCs are maintained and renewed within tissues. We generated a single cell atlas of lung ILC2s and found that Il18r1+ ILCs comprise circulating and tissue-resident ILC progenitors (ILCP) and effector-cells with heterogeneous expression of the transcription factors Tcf7 and Zbtb16, and CD103. Our analyses revealed a continuous differentiation trajectory from Il18r1+ ST2- ILCPs to Il18r- ST2+ ILC2s, which was experimentally validated. Upon helminth infection, recruited and BM-derived cells generated the entire spectrum of ILC2s in parabiotic and shield chimeric mice, consistent with their potential role in the renewal of tissue ILC2s. Our findings identify local ILCPs and reveal ILCP in situ differentiation and tissue adaptation as a mechanism of ILC maintenance and phenotypic diversification. Local niches, rather than progenitor origin, or the developmental window during ontogeny, may dominantly imprint ILC phenotypes in adult tissues.

IL-4/IL-13-producing ILC2s are required for timely control of intestinal helminth infection in mice.

Infection of mice with Nippostrongylus brasiliensis (Nb) serves as a model for human hookworm infection affecting about 600 million people world-wide. Expulsion of Nb from the intestine requires IL-13-mediated mucus secretion from goblet cells and activation of smooth muscles cells. Type 2 innate lymphoid cells (ILC2s) are a major cellular source of IL-13 but it remains unclear whether IL-13 secretion from ILC2s is required for Nb expulsion. Here, we compared the immune response to Nb infection in mixed bone marrow chimeras with wild-type or IL-4/IL-13-deficient ILC2s. ILC2-derived IL-4/IL-13 was required for recruitment of eosinophils to the lung but had no influence of systemic eosinophil levels. In the small intestine, goblet cell hyperplasia and tuft cell accumulation was largely dependent on IL-4/IL-13 secretion from ILC2s. This further translated to higher eggs counts and impaired worm expulsion in mice with IL-4/IL-13-deficient ILC2s. Overall, we demonstrate that ILC2s constitute a non-redundant source of IL-4/IL-13 required for protective immunity against primary Nb infection.

Th2 cell-derived IL-4/IL-13 promote ILC2 accumulation in the lung by ILC2-intrinsic STAT6 signaling in mice.

Infection of mice with the gastrointestinal helminth Nippostrongylus brasiliensis elicits profound local proliferation and accumulation of type 2 innate lymphoid cells (ILC2s) in the lung. The regulation of ILC2 proliferation and accumulation in the lung is poorly understood. Using T cell-specific IL-4/IL-13-deficient mice, we demonstrate that IL-4/IL-13 secretion from Th2 cells promotes proliferation and expansion of the ILC2 population in the lung of N. brasiliensis-infected mice. Competitive mixed BM chimeras containing normal and STAT6-deficient ILC2s further indicated that ILC2s have to respond directly to IL-4/IL-13 for this effect while STAT6 is not required for IL-13 production in ILC2s. In addition, expression of a constitutively active form of STAT6 in ILC2s was sufficient to promote their proliferation in uninfected mice. The expression of MHC class II in ILC2s appeared to be enhanced by STAT6 signaling supporting the concept that Th2 cells and ILC2s can communicate in an antigen-dependent manner resulting in a Th2-regulated accumulation of ILC2s in the lung during an acute type 2 immune response. Based on our observations, targeting the STAT6 pathway in ILC2s could help to develop new treatments to dampen ILC2 proliferation in the lung and thereby ameliorate ILC2-mediated allergic inflammation.

Selective expression of constitutively activated STAT6 in intestinal epithelial cells promotes differentiation of secretory cells and protection against helminths.

Intestinal epithelial cells (IECs) constitute an important barrier between host and pathogen. Immune mechanisms that provide protection against gastrointestinal helminths often require IL-4Rα-induced activation of STAT6-regulated genes in IECs. However, it is not known whether STAT6 activation in IECs enhances protective immunity against helminths. Furthermore, the regulation of proliferation and differentiation processes of the intestinal epithelium by IEC-intrinsic STAT6 signaling remains unclear. To address these questions, we generated mice with specific expression of a constitutively active version of STAT6 in IECs. These VillinCre_STAT6vt mice show accumulation of secretory IECs, increased proliferation of IECs and lengthening of the small intestine. They rapidly expelled Nippostrongylus brasiliensis worms even in the absence of T cells. Furthermore, primary infection with Heligmosomoides polygyrus resulted in larval trapping in the submucosa and the fecundity of adult worms was severely impaired. Our results reveal an important IEC-intrinsic role of STAT6-regulated genes for intestinal homeostasis and protective immunity against helminths.

A CCL1/CCR8-dependent feed-forward mechanism drives ILC2 functions in type 2-mediated inflammation.

Group 2 innate lymphoid cells (ILC2s) possess indispensable roles during type 2-mediated inflammatory diseases. Although their physiological and detrimental immune functions seem to depend on the anatomical compartment they reside, their tissue tropism and the molecular and immunological processes regulating the self-renewal of the local pool of ILC2s in the context of inflammation or infection are incompletely understood. Here, we analyzed the role of the CC-chemokine receptor CCR8 for the biological functions of ILC2s. In vitro and in vivo experiments indicated that CCR8 is in comparison to the related molecule CCR4 less important for migration of these cells. However, we found that activated mouse and human ILC2s produce the CCR8 ligand CCL1 and are a major source of CCL1 in vivo. CCL1 signaling to ILC2s regulates their proliferation and supports their capacity to protect against helminthic infections. In summary, we identify a novel chemokine receptor-dependent mechanism by which ILC2s are regulated during type 2 responses.

Interactions between Innate Lymphoid Cells and Cells of the Innate and Adaptive Immune System.

Type 2 innate lymphoid cells (ILC2s) are a major source of cytokines, which are also produced by Th2 cells and several cell types of the innate immune system. Work over the past few years indicates that ILC2s play a central role in regulating type 2 immune responses against allergens and helminths. ILC2s can interact with a variety of cells types of the innate and adaptive immune system by cell-cell contacts or by communication via soluble factors. In this review, we provide an overview about recent advances in our understanding how ILC2s orchestrate type 2 immune responses with focus on direct interactions between ILC2s and other cells of the immune system.