The major histocompatibility complex (MHC) includes genes that encode which of the following proteins?

A. HLA-A.

B. HLA-DR.

C. TAP-1.

D. 21-Hydroxylase.

DISCUSSION: The major histocompatibility complex (MHC) includes genes encoding histocompatibility antigens, some other proteins, and a number of pseudogenes that do not encode proteins. The class I region encodes more than 15 genes, including the classical transplant genes A, B, and C as well as HLA-E, F, and G and four pseudogenes, H, J, K, and L. The class II region contains more than 25 genes, including those for the transplantation antigens HLA-DR, DQ, and DP. The region also includes two alpha genes, DMA and DNA, and two beta genes, DMB and DOB, genes for the low-molecular-weight proteins (LMPs) LMP2 and LMP3 and for the transporter molecules TAP1 and TAP2. The class III region, lying between class II and class I, contains more than 30 genes, among which are the genes encoding the complement components factor B, C2, and both C4 molecules, both tumor necrosis factor genes alpha and beta, and the heat shock proteins Hsp 1H and Hsp 70 2, and 21-hydroxylase.