HLA-C and autoimmune disease: CD is a T cell-mediated autoimmune disorder caused by gluten proteins with both major histocompatibility complex (MHC) and non-MHC genes included in the list of predisposing genetic factors.[43,44] MHC is a group of genes that code for cell surface proteins that function in the adaptive immune system.[45] HLA genes are proteins that express their gene products on the surface of leukocytes and help regulate the immune system.[45] The MHC region includes HLA genes, which are further subdivided into 3 regions that contain highly polymorphic genes.