Abstract
Abstract The C1858T polymorphism in the Ptpn22 gene is associated with increased susceptibility to several autoimmune disorders including Type 1 Diabetes (T1D). This produces a gain-of-function R620W variant with diminished binding affinity to Csk, which, like PTPN22 is an inhibitor of antigen receptor signaling. In the T1D-prone BioBreeding (BB) rat, this gene is located in the Iddm3 locus on chromosome 2, making it a likely candidate gene. Sequencing revealed a non-synonymous SNP causing an A629T substitution C-terminal to the PTPN22 P1 domain that binds to Csk. Co-immunoprecipitations examining the PTPN22-Csk interaction have shown a 2-fold reduction in binding affinity of the BB compared to the ACI variant. Importantly, a genome-wide segregation analysis of an F2(BBxACI.1u.lyp) cohort revealed the dominant effect of the BB allele to confer a 3-fold increased T1D risk compared to the allele carried by the T1D-resistant ACI strain. Homozygosity for the BB allele is also associated with phenotypes indicative of immune dysregulation including increased proportions of activated CD4 T cells in the periphery. Reminiscent of the phenotypes observed in T1D patients carrying the R620W variant, BB-derived T and B cells exhibit hyporesponsiveness to antigen receptor engagement, with a concomitant decrease in IL-2 production by CD4 T cells. Banting and Best Diabetes Centre, Genome Canada, Ontario Research Foundation and CIHR
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