IL-22 Fate Reporter Reveals Origin and Control of IL-22 Production in Homeostasis and Infection

Abstract

Interleukin 22 (IL-22) is a cytokine that regulates tissue homeostasis at barrier surfaces. A variety of IL-22 producing cell types are known, but identification on the single cell level remains difficult. We therefore generated a fate reporter mouse that would allow the identification of IL-22 producing cells and their fate mapping in vivo. To trace IL-22 expressing cells, a sequence encoding Cre recombinase was cloned into the Il22 locus and Il22Cre mice were crossed with reporter mice expressing enhanced yellow fluorescence protein (eYFP) under control of the endogenous Rosa26 promoter. In IL22CreR26ReYFP mice, the fluorescent reporter permanently labels cells that have switched on Il22 expression irrespective of cytokine production. Despite a degree of underreporting, eYFP expression was detectable in non-immune mice and restricted to innate lymphoid cells (ILC3) in the gut and γδ T cells in skin or lung. Upon skin challenge with imiquimod, eYFP+ γδ and CD4 T cells expanded in the skin. Infection with Citrobacter rodentium was initially controlled by ILC3, followed by expansion of eYFP+ CD4 T cells, which were induced in innate lymphoid follicles (ILF) in the colon. No eYFP expression was detected in small intestinal Th17 cells and they did not expand in the immune response. Colonic eYFP+ CD4 T cells exhibited plasticity during infection with expression of additional cytokines in contrast to ILC3, which remained largely stable. Single cell qPCR analysis of eYFP+ CD4 T cells confirmed their heterogeneity, suggesting IL-22 expression is not strictly confined to particular subsets or a dedicated Th22 subset.

The role of barrier function, autophagy, and cytokines in maintaining intestinal homeostasis

“…IL-22 signalling restores barrier function during inflammation and its protective role for the gut mucosa has also been demonstrated in mouse models of colitis. In the intestine, IL-22 promotes wound healing, tissue regeneration, and epithelial cell proliferation [106,107]. It regulates epithelial-microbial homeostasis through the induction in IECs of anti-microbial peptides, specifically of the Reg family, including RegIIIβ and RegIIIγ, as well as β-Defensin 2 and β-Defensin 3 [103,108].…”

Innate Lymphoid Cells in Graft-Versus-Host Disease

“…Thus, IL‐22 appears as a crucial host‐derived factor modulating susceptibility to GVHD (Figure 2). The known cellular sources of IL‐22 are T cells and ILC3 and very recently an IL‐22 reporter mouse revealed that the major and most stable IL‐22‐producing cells are the NKp46 − CD4 − ILC3, while only a minority of NKp46 + ILC3 expressed IL‐22 35. In line with these recent findings, only IL‐22 produced by the IL‐23‐responsive RORγt + CCR6 + NKp46 − ILC3 proved to be essential in the protection against GVHD 9.…”

Harnessing the plasticity of CD4+ T cells to treat immune-mediated disease

“…Reprogramming between distinct CD4 + T cell subsets can be observed in human and mouse T cells under certain conditions in vitro [16][17][18][19] or in mice in vivo on transferring highly purified popu lations of cells [20][21][22][23][24][25] . By using lineage-tracing systems in mice, in which cells are engineered to express Cre recombinase under the control of transcriptional elements that regulate key polarization factors (such as cytokines or transcription factors) and a fluorescent protein reporter of Cre activity, endogenously polarized CD4 + T cells from many subsets have been found to change phenotype during their lifespan [26][27][28][29] . In humans, the combination of pheno typic analyses and sequencing of T cell receptors (TCRs), which act as unique barcodes for each T cell, has made it possible to investigate the phenotype of clonal descendants of single cells.…”