Project Summary/Abstract Type 1 diabetes (T1D) is a multifactorial autoimmune disease that requires genetic susceptibility as well as environmental triggers such as viral infections in triggering disease onset. One viral infection that is highly correlated with T1D is the Coxsackievirus B (CVB) serotype. Sensing of CVB is mediated by the melanoma differentiation-associated protein 5 (MDA5), a cytosolic sensor of dsRNA, which is encoded by the IFIH1 gene. Stimulation of the MDA5 signaling pathway activates the transcription factors IRF3 and NF-κB p65, which induce Type I IFNs synthesis, which through autocrine signaling initiate an antiviral transcriptional program. Single nucleotide polymorphisms (SNPs) in the IFIH1 gene such as rs1990760, which results in a non-synonymous mutation that changes alanine at position 946 to a threonine, is highly associated with increased risk for T1D. Studies in human PBMCs and mice have demonstrated that the A946T SNP results in an increased sensitivity to viral ligands and subsequently a stronger downstream IFN response. Macrophages have been shown previously to play an important role in T1D initiation, however, the response of β-cells to viral infection is also important. Our central hypothesis is that T1D-associated SNPs result in an exacerbated islet-resident macrophage immune response and β-cell inflammatory response following CVB3 infection which contributes to the initiation of autoimmunity. This will be tested using monocyte- derived macrophages and dendritic cells and induced pluripotent stem cells engineered to become human pancreatic β-cells from healthy donors and patients with T1D that are genotyped for IFIH1 SNPs that contribute to T1D susceptibility and resistance.