MHC Genes and Their Products
المؤلف:
APURBA S. SASTRY , SANDHYA BHAT
المصدر:
Essentials Of Medical Microbiology 2021
الجزء والصفحة:
3rd edition , p178-179
2025-09-04
469
In humans, HLA complex coding for MHC proteins are located in short arm of chromosome-6. The HLA complex extends over 4000 kbp length covering >100 genes. The genes are clustered in three regions named as MHC region-I, II and III (Fig. 1).
Fig1. Structure of human MHC complex.
MHC Region-I
It is about 2000 kbp in length, comprises of three class I genes called HLA-A, HLA-B and HLA-C genes which code for HLA-A, HLA-B and HLA-C proteins respectively, each one is capable of forming the α-chain of MHC class I molecules.
* MHC-I proteins are located on the surface of all nucleated cells (except sperm cells) and platelets. They are absent in RBCs
* They present the peptide antigen to CD8 T cells.
MHC Region-II
It spans over 1000 kbp length; comprises of three regions— (1) DP, (2) DQ and (3) DR genes encoding DP, DQ and DR proteins respectively, each one is capable of forming the α and β-chain of MHC class II molecules. In addition, MHC II region also contains certain other non-classical genes, such as DO, DM, LMP and TAP (transporter associated with antigen processing) that help in antigen processing and presentation.
* MHC-II proteins are located on the surface of antigen presenting cells
* They present the peptide antigen to CD4 T cells.
MHC Region-III
It is also 1000 kbp in length. It is not involved in antigen presentation, instead it carries genes that code for complement factors (C2, C4, C3 convertase, factor B and properdin), heat shock protein (HSP70) and tumor necrosis factor (TNF-α and β) and steroid 21-hydroxylases.
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