HLA-DPA1 and type 1 diabetes mellitus: Multiple major histocompatibility complex (MHC) class II genes involved in antigen presentation (HLA-DPA1, HLA-DRB1, and HLA-DQA1) were upregulated across Stage 1 T1D B cell subsets (Fig. 2), as was observed in autoantibody positive and Stage 3 T1D individuals.17