Major Histocompatibility Complex (MHC): Classification, Structure and immune response in Animals
Susmita Majumder1, Santanu Nath2
- Division of Physiology & Climatology, ICAR-IVRI Bareilly (U.P.)
- Division of Livestock Products Technology, ICAR-IVRI Bareilly (U.P.)
INTRODUCTION
A group of surface proteins called the Major Histocompatibility Complex (MHC) are found on the cell membrane of nucleated cells. It is more crucial for identifying the antigen in a self- and non-self body, recognizing intracellular structures, and being in charge of antigen presentation. Histo refers to tissues. Compatibility refers to living together harmoniously. MHC molecules always recognize only T lymphocytes. The two types of MHC are worked in immunity. T helper (Th) cell recognized by MHC molecules II, and T cytotoxic (Tc) cells are recognized by MHC I molecules.
DEFINITION
“The membrane-attached protein known as the major histocompatibility complex works to recognize antigen in both self- and non-self bodies and to deliver antigens. “.
MHC’s biological purpose MHC limitation is a phenomenon that occurs when an antigen is presented to start an immune response. Using the MHC class I molecule, endogenous Ag is delivered to CD8 T cells. MHC class II molecule, which participates in both humoral and cell-mediated immunity, presents exogenous Ag to CD4 T cell. Serve as structures that present antigen.
CLASSIFICATION
Class I & II MHC Molecules -membrane bound glycoproteins
- Class III MHC Molecules are structurally and functionally closely related.
- Multiple unrelated protein groups
- Do not share any similarity to class I and II molecules.
- Participates in other aspects of immune response
Class I MHC Molecules
- All nucleated cells, platelets
- Present intracellular antigens to CD8+ T cells
- Consists of two polypeptide chains
- α chain-45 kDa
- β chain – 12 kDa
- Class I MHC Molecule α Chain
- 3 external domains – Each approximately 90 amino acids long.
- A transmembrane domain – 25 hydrophobic amino acids and a short chain of charged hydrophilic amino acids.
- A cytoplasmic anchor segment- 30 amino acid long.
CLASS I MHC MOLECULE
- β2 Microglobulin-Similar in size and organization to α3 domain
- No transmembrane region
- Bound non covalently to α domain
CLASS II MHC MOLECULE
- Antigen presenting cells
- Present extracellular antigens to CD4+ T cells
- Consists of two different polypeptide chains
- α chain-33 kDa
- ẞ chain-28 kDa
MHC CLASS II MOLECULE
- Antigen presenting cells
- Level of expression significantly increases after activation.
- APCs differ by
- Mechanism of antigen uptake
- Constitutive expression of class II MHC molecule.
- Inherent co-stimulatory activity.
PROFESSIONAL APC
- DENDRITIC CELLS-
- Most effective
- Constitutively express high levels of MHC class II molecule
- Inherent co-stimulatory activity
- Activate naive T cells.
- MACROPHAGES- to be activated before they express sufficient level of MHC class II molecule and co-stimulatory activity.
- B CELLS-
- Constitutively express MHC class II molecule
- To be activated for co-stimulatory activity.
- NON PROFESSIONAL APC
- Fibroblasts Glial cells 3.Pancreatic B cells 4.Thymic epithelial cells 5.Thyroid epithelial cells 6.vascular endothelial cell
- MHC and immune response
- MHC molecules engage with the foreign antigen as well as the complementary structure of other immune cells to produce an immune response that is particular to the antigen that is causing it.
- Identity at the MHC is required for the T-/B-cell cooperation required for antibody production and for the development of germinal centers in the spleen.
- The in vitro proliferation of T cells in response to particular antigen in the presence of APCs, which is a measure of the interaction between APCS and T cells, is also MHC-restricted.
- The B-F/B-L antigens are the restriction elements for all of these cellular interaction phenomena.
- Due to restriction elements or through particular MHC-linked immune response genes, the MHC influences the genetic control of immuno responsiveness.
- The animal MHC is associated with the generation of antibodies against a wide range of antigens, including the immunological response to synthesized polypeptides.
- In order to eliminate invasive infections, complement proteins play a crucial role in the immune response. The MHC in Animals has been linked to the total serum hemolytic complement levels.
Conclusion: MHC is the most important complex of animal immune system. If it isn’t functioning properly, animals’ immune systems weaken and they become more susceptible to illness. To prevent this kind of issue, the MHC in an animal’s immune system needs to function properly.
