Characterization of Rat ILCs Reveals ILC2 as the Dominant Intestinal Subset.

Ahmed Abidi,Gaëlle Bériou,Cédric Louvet,Thomas Laurent,Jérôme Martin,Laurence Bouchet-Delbos,Raja Triki-Marrakchi,Cynthia Fourgeux,Régis Josien,Jeremie Poschmann

doi:10.3389/fimmu.2020.00255

Abstract

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes that lack antigen-specific receptors and exhibit innate effector functions such as cytokine production that play an important role in immediate responses to pathogens especially at mucosal sites. Mouse and human ILC subsets have been extensively characterized in various tissues and in blood. In this study, we present the first characterization of ILCs and ILC subsets in rat gut and secondary lymphoid organs using flow cytometry and single cell RNA sequencing. Our results show that phenotype and function of rat ILC subsets are conserved as compared to human and mouse ILCs. However, and in contrast to human and mouse, our study unexpectedly revealed that ILC2 and not ILC3 was the dominant ILC subset in the rat intestinal lamina propria. ILC2 predominance in the gut was independent of rat strain, sex or housing facility. In contrast, ILC3 was the predominant ILC subset in mesenteric lymph nodes and Peyer patches. In conclusion, our study demonstrates that in spite of highly conserved phenotype and function between mice, rat and humans, the distribution of ILC subsets in the intestinal mucosa is dependent on the species likely in response to both genetic and environmental factors.

Highlights

Innate lymphoid cells (ILCs) are recombination-activating genes (RAGs)-independent lymphocytes that can be divided into three subsets, namely ILC1, ILC2, and ILC3, based on the cytokines they produce and the transcription factors (TFs) guiding their differentiation [1]
Almost no expression of recombination activating gene 1 (Rag1) was detected in Lin− CD127+ cells as compared to total mesenteric lymph nodes (MLN) cells (Figure 1C). We assessed whether these candidate ILCs could be further separated based on their differential intracellular expression of the TFs GATA-3 and RORγt, which usually define human and mouse ILC2 and ILC3, respectively [31]
We identified three populations of Lin− CD127+ as GATA-3− RORγt−, GATA-3+ RORγt−/low, and GATA-3− RORγt+ cells, possibly corresponding to populations of ILC1, ILC2, and ILC3 (Figure 1A)

Summary

Introduction

Innate lymphoid cells (ILCs) are recombination-activating genes (RAGs)-independent lymphocytes that can be divided into three subsets, namely ILC1, ILC2, and ILC3, based on the cytokines they produce and the transcription factors (TFs) guiding their differentiation [1]. ILCs are characterized by their capacity to respond rapidly to tissue damage and/or infection by producing sets of effector cytokines matching those of T helper cell subsets [2]. GATA-3+ ILC2 respond to IL-25, IL-33, and TSLP by producing key mediators of immune responses against helminths such as IL-5, IL-9, and IL-13 [4]. A subset of regulatory ILCs (ILCreg), which produces IL-10 and TGF-β, has been described recently. These cells do not express FOXP3 and have been implicated in the resolution of inflammation during colitis [9]

Methods

Results

Conclusion