The Natural Cytotoxicity Receptor NKp46 Is Dispensable for IL-22-Mediated Innate Intestinal Immune Defense against Citrobacter rodentium

Abstract

Natural cytotoxicity receptors (including NKp30, NKp44, and NKp46 in humans and NKp46 in mice) are type I transmembrane proteins that signal NK cell activation via ITAM-containing adapter proteins in response to stress- and pathogen-induced ligands. Although murine NKp46 expression (encoded by Ncr1) was thought to be predominantly restricted to NK cells, the identification of distinct intestinal NKp46+ cell subsets that express the transcription factor Rorc and produce IL-22 suggests a broader function for NKp46 that could involve intestinal homeostasis and immune defense. Using mice carrying a GFP-modified Ncr1 allele, we found normal numbers of gut CD3−GFP+ cells with a similar cell surface phenotype and subset distribution in the absence of Ncr1. Splenic and intestinal CD3−NKp46+ cell subsets showed distinct patterns of cytokine secretion (IFN-γ, IL-22) following activation via NK1.1, NKp46, IL-12 plus IL-18, or IL-23. However, IL-22 production was sharply restricted to intestinal CD3−GFP+ cells with the CD127+NK1.1− phenotype and could be induced in an Ncr1-independent fashion. Because NKp46 ligands can trigger immune activation in the context of infectious pathogens, we assessed the response of wild-type and Ncr-1-deficient Rag2−/− mice to the enteric pathogen Citrobacter rodentium. No differences in the survival or clinical score were observed in C. rodentium-infected Rag2−/− mice lacking Ncr1, indicating that NKp46 plays a redundant role in the differentiation of intestinal IL-22+ cells that mediate innate defense against this pathogen. Our results provide further evidence for functional heterogeneity in intestinal NKp46+ cells that contrast with splenic NK cells.

A point mutation in the Ncr1 signal peptide impairs the development of innate lymphoid cell subsets

“…45,46 Loss of Ncr1 has previously been shown not to affect ILC3 development with Ncr1 gfp/gfp Rag2 −/- mice showing survival and clinical scores similar to control mice when challenged with the enteric infection Citrobacter rodentium . 47 In this setting, NKp46 expression did not appear to be essential for protection.…”

Innate‐like CD8+ T‐cells and NK cells: converging functions and phenotypes

“…There also seems to be some plasticity between ILC1 and ILC3 cells 32, 33. Thus, ILCs secreting both IFN γ and IL‐17 in response to IL‐23, or IFN γ and IL‐22 in response to IL‐12+IL‐18 have been reported 26, 34. It is thought that both NK cells and ILC1s depend on IL‐15 for their development,35, 36, 37, 38 which is in contrast to ILC2s and ILC3s, which rely on IL‐7 and are depleted in IL‐7R α −/− mice 19, 39…”

Phenotypic and Functional Plasticity of Murine Intestinal NKp46+ Group 3 Innate Lymphoid Cells

“…Cytokine production in human ILC3 can be stimulated by anti-NKp44 Abs (11), although the ligands that can mimic this activity in vivo remain unknown. In the mouse, Ncr1 ablation (in Ncr1 GFP/GFP mice) has little impact on ILC3 homeostasis, and cytokine responses to pathogenic Citrobacter rodentium are unaffected (12). Modulation of NKp46 expression on NK cells occurs during mouse CMV infection (13) and may "tune" ILC3 responses in a fashion similar to that proposed for "licensing" of cytokine and cytotoxic responses of NK cells via NKp46 (14).…”