Delineating the function of MHC class III genes in antigen presenting myeloid cell contribution to autoimmunity

SUMMARY The MHC class locus has been associated with several diseases. Notably, genome-wide population studies have identified pivotal polymorphisms within MHC class III (MHC-III) genes that are directly associated with autoimmune diseases, including type 1 diabetes (T1D), intestinal bowel disease (IBD), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), among others. Although less understood, variations in expression patterns of MHC-III genes correlate with disease severity, both dependent and independent from predisposition-related polymorphisms within the MHC class I and II regions. This would suggest that MHC-III genes can govern immunity vs. tolerance in autoimmune settings, with genetic variations potentially increasing susceptibility to disease severity. However, much remains unknown regarding the underpinning mechanistic functions of MHC-III genes in directing autoimmunity. This major gap prevents our understanding of the collective and interconnective roles of these clustered genes in health and disease. Furthermore, this continues to limit clinical success in immune-based therapies largely due to our incomplete knowledge of governing factors driving myeloid cell biology. This is important as failures in the function of antigen presenting myeloid cells, such as dendritic cells (DC) and macrophages, can cause organ-specific and systemic autoimmune diseases. Therefore, it is the long-term objective of these studies to determine the underlying mechanistic role of MHC-III genes in antigen presenting myeloid cells and their contribution to inflammatory diseases. To help resolve the existing knowledge gap within the field, the proposed set of investigations will determine the functional role of MHC-III genes in driving pro-inflammatory responses (Aim 1) and their role in priming autoreactive T cell responses (Aim 2). Extensive preliminary investigations have performed an unbiased high-throughput transcriptomic profiling coupled with RNAi screening to identify key MHC-III genes believed to play key functional roles in macrophages and DC. In Aim 1, studies will intricately evaluate the role of candidate MHC-III genes in macrophages in vitro using a novel 3D organoid. The studies will additionally define the mechanisms of key MHC-III genes in initiating and sustaining inflammation in vivo using both insulitis and colitis autoimmune mouse models. For Aim 2, investigations will describe the pivotal role of MHC-III genes in governing the priming of T cells in vivo. Studies will monitor changes in frequency, infiltration and effector responses of autoantigen-specific T cells in absence of key MHC-III genes within DC subsets to rigorously define their immunoregulatory roles. Collectively, understanding the determinants of MHC-III genes in regulating macrophage and DC biology under autoimmune conditions would have broad implications for effective design of novel immunotherapies.