Major Histocompatibility Complex (MHC) antigens are a set of cell surface proteins essential for the acquired immune system to identify foreign molecules. MHC antigens bind to pathogen antigens and display them on the cell surface for identification by T-cells. MHC is a cluster of genes on chromosome 6 in humans that encodes these antigens. There are three classes of MHC - Class I presents antigens to CD8 T-cells on all nucleated cells, Class II presents antigens to CD4 T-cells on antigen presenting cells like macrophages, and Class III plays a role in immune function through complement and cytokines. MHC antigens act as antigen presenting structures and play important roles in immune responses, transplantation tissue matching, and autoimmune diseases.

1. STRUCTURE & FUNCTIONS OF MHC
Mr. A. T. Sharma
Assist. Professor
Nanded Pharmacy College, Nanded

2. MHC Antigens
• A set of cell surface proteins in all human beings and vertebrates
called Major Histocompatibility Complex antigens
• Essential for acquired immune system to identify foreign molecules.
• Bind to antigens of pathogens and display (present) them on the
cell surface for identification by T-cells
• MHC is a tightly linked cluster of genes present on chromosome 6
in humans and chromosome 17 in mouse which encodes MHC
antigens
• Discovered from antigenic differences in WBCs of different
individuals, so called as Human Leukocyte Antigens (HLA), (in
mouse, H-2 genes)
• George Snell from USA (1950) – concept of MHC participation in
transplant rejection (Nobel Prize in 1980)
• Only identical twins have exactly same MHC molecules
• Matched during organ transplantation – tissue typing (HLA-DR
antigens matched)
• Susceptibility to autoimmune disorder

3. Classes:
Class I:
• They secrete glycoproteins, called Class-I MHC molecule
• Expressed on the surface of all nucleated cells (Antigen
presenting cells)
• Present the peptide antigens to TC cells
• Have β2 subunits - recognized only by CD8 co-receptors on
TC cells
Class II:
• They secrete glycoproteins, called Class-II MHC molecule
• Expressed on the surface of macrophages, dendritic cells,
epithelium of thymus, some endothelial cells and B-cells
(Antigen presenting cells)
• Present the peptide antigens to TH cells
• Have β1 and β2 subunits - recognized only by CD4 co-
receptors on TH cells

4. Class III:
• They consists of complement components C4,
C2, Factor B, inflammatory cytokines including
TNF, heat shock proteins (Play a role in
immune function)
• Located between Class I and Class II genes

5. APC Cells with MHC

6. Structure of Class I and Class II MHC

7. Functions of MHC
• Act as antigen presenting structure – role in
cell mediated and humoral immune response
• Play a role in development of autoimmune
diseases
• Tissue typing during organ transplantation
• In graft versus host response
• Class III MHC play a role in immunity through
complement system and in inflammatory
response.

8. Thank You…!!!