Regulation and Heterogeneity of Pancreatic Natural Killer Cells During Type 1 Diabetes

Abstract

The vertebrate immune system contains a diverse inventory of genetic, epigenetic, molecular and cellular mechanisms dedicated to distinguishing and to determining appropriate responsiveness to "self" and "non-self." Autoimmune diseases such as type 1 diabetes (T1D), caused by immune destruction of insulin-producing beta cells in the pancreas, are the result of breakdowns in these mechanisms. Recent T1D research efforts have uncovered the opposing functions of pancreatic Foxp3+ regulatory T \((T_{reg})\) cells and natural killer (NK) cells as critical determinants of tolerance versus autoimmunity. Here, we examine the extrinsic adaptive regulation of NK cells by \(T_{reg}\) cells, and profile the tissue-specific heterogeneity of NK cells for intrinsic mediators of NK cell tolerance. Depletion of \(T_{reg}\) cells in the BDC2.5/NOD model resulted in destruction of pancreatic islets and a high penetrance of T1D. Prior to the activation of T cells, there was a rapid and localized activation of pancreatic NK cells, including their proliferation and production of diabetogenic \(IFN-\gamma\). How \(T_{reg}\) cells exerted their dominant tolerance on NK cells in this setting was unclear. We explored the molecular mechanisms underlying this NK/\(T_{reg}\) cell axis, following leads from a kinetic exploration of gene-expression changes early after punctual perturbation of \(T_{reg}\) cells. Our data supported a scenario in which \(T_{reg}\) cells controlled NK cell functions by limiting the bioavailability of T cell-derived IL-2 in the islets, representing a novel intertwining of innate and adaptive immunity. Cell intrinsic regulatory mechanisms, such as the expression of the Ly49 receptor family during NK cell education, tune NK cells to be functionally self-tolerant. However, the transcriptional repertoire of Ly49 receptors had never been comprehensively explored. We performed RNAseq-based profiling of the Ly49 receptors, and uncovered a subtle difference in the expression of Ly49E and Ly49H on pancreatic NK cells compared to spleen. We also expanded the phenotypic profiling of pancreatic NK cells using high-dimensional mass cytometry and uncovered greater diversity than had previously been described. Taken together, these studies highlighted a new degree of heterogeneity in pancreatic NK cells and uncovered a novel regulatory mechanism, originating from the adaptive immune system, responsible for maintaining NK cell tolerance.