The human MHC (human leukocyte antigen; HLA) consists of a linked set of genes encoding major glycoproteins involved in antigen presentation. The complex locates to the sho arm of chromosome 6 and divides into three separate regions: class I, class II, and class III genes. The class I "classic" region encodes HLA-A, HLA-B, and HLA-C loci; the nonclassic or class I-related region encodes HLA-E, HLA-F, and HLA-G loci and other immunity-related genes such as CD1. The class II region (HLA-D) encodes HLA-DP, HLA-DQ, and HLA-DR loci and other genes related to antigen processing, transpo, and presentation, such as, transpoer associated with antigen processing (TAP). The class III region encodes genes for tumor necrosis factors and (TNF- and TNF-); complement factors C2, C4, and B; and the steroidogenic enzyme 21-hydroxylase. Ref: Jaume J.C. (2011). Chapter 2. Endocrine Autoimmunity. In D.G. Gardner, D. Shoback (Eds), Greenspan's Basic & Clinical Endocrinology, 9e.