Endogenous glucocorticoids control host resistance to viral infection through the tissue-specific regulation of PD1 expression on NK cells

Purpose: Controlling the balance between immunity and immunopathology is crucial for host resistance to pathogens. Upon infection, activation of the hypothalamic-pituitary-adrenal (HPA) axis leads to the production of glucocorticoids (GCs). However, the pleiotropic effects of these steroid hormones make it difficult to decipher their precise role in vivo. Our purpose was to study how GCs regulate the function of group 1 ILCs in spleen and liver upon Murine Cytomegalovirus (MCMV) infection. Methods: We studied the in vivo effect of endogenous GCs released upon MCMV infection on NK cells in spleen and liver and ILC1s in the liver. We compared WT mice with GRNcr1-iCre mice, in which the gene encoding for GC receptor (GR) is selectively deleted in Ncr1+ cells. Results: We found that the regulation of NK function by the GR is required for host protection against MCMV. Mechanistically, endogenous GCs produced shortly after infection induce the selective and tissue-specific expression of the immune checkpoint PD1 on NK cells. This GC-PD1 pathway mediates its immunoregulatory functions by limiting interferon (IFN)-g production by splenic NK cells, preventing lethal immunopathology. Importantly, this regulation does not compromise viral clearance. Conclusions:The fine-tuning of a selective subset of ILCs by the HPA axis preserves tissue integrity without impairing pathogen elimination, revealing a novel aspect of neuro-immune regulation. Overall design: Splenocytes (after NK cell enrichment with the mouse NK Cell Isolation Kit II, Miltenyi Biotec) and liver lymphocytes were pooled from three mice for each genotype. A FACS Aria III (BD Biosciences) was used to sort approximately 5 x 10^5 NK cells from the spleen and liver and 5 x 10^4 liver-resident ILC1s 44h post MCMV infection. We compared gene expression between glucocorticoid receptor (GR)-sufficient and deficient ILCs to identify the genes whose expression is regulated by GCs. Three biological replicates were generated for all samples except for the GRNcr1-iCre liver ILC1s sample (two biological replicates).

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Quatrini L, Wieduwild E, Escaliere B, Filtjens J, Chasson L, Laprie C, Vivier E, Ugolini S