Human leukocyte antigen (HLA) DRB1*0405-DQB1*0401 haplotype, substitution of aspartic acid at DQB1 46 [42, 43] and single nucleotide polymorphism in cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), which is expressed on CD4+ and CD8+ T cells and important for the regulation of T cell stimulation [44, 45], are discussed as key genetic factors in AIP. Here, CD4 is linked to autoimmune pancreatitis.