Genetic risk alleles as drivers of loss of anergic B cells in autoimmunity

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Project Summary/Abstract Type 1 diabetes (T1D) is an autoimmune disorder characterized by destruction of the pancreatic beta cells, leading to decreased production of insulin and hyperglycemia. Although environmental factors contribute, genetic factors are likely the primary determinants of risk. With recent advances in GWAS studies, hundreds of risk-conferring alleles have been discovered for T1D. For most cases the exact mechanisms by which these genes and their gene products contribute to development of autoimmunity remains to be elucidated. However, given that T1D requires the activation of autoantigen-specific T and B cells that are normally silenced by immune tolerance, it is likely a combination of HLA and non-HLA alleles act in concert to undermine normal tolerance mechanisms, allowing activation of these autoreactive cells. Although T cells are the primary effectors of beta cell destruction in T1D, autoreactive B cells are thought to act primarily as antigen presenting cells. In a healthy individual, autoreactive B cells are normally silenced by one of three mechanisms: receptor editing, clonal deletion, or anergy. In our recent publication, we determined B cells bearing antigen receptors with high affinity for insulin are found only in the anergic B cell compartment, termed BND, of healthy individuals. Importantly, these cells leave this compartment in a proportion of first-degree relatives (FDRs), and in all autoantibody positive pre-diabetics and new onset diabetics. We hypothesize people at risk for development of T1D carry autoimmune risk alleles that impair proper silencing of autoreactive B cells by anergy, allowing these cells to become activated and contribute to disease. In this application we propose studies to analyze the association of loss of anergic B cells with high risk genotype alleles known to contribute to maintenance of B cell anergy. Aim 1 will explore in FDRs of T1D patients the association between loss of BNDs and risk allele genotype. Aim 2 will examine the relationship of loss of anergic B cells with the high risk T1D genotype allele, Ptpn22, using a mouse model. The potential impact of these studies will lie in understanding how risk alleles conspire to undermine maintenance of immune tolerance to autoantigens in T1D.