Veterinary Immunology and Serology

Histocompability antigen

HISTOCOMPATIBILITY ANTIGEN

• When an organ is grafted, normally the graft is rejected because of immune response.
• The antigen present on the cells of the graft tissues trigger the immune response and these antigens are called histocompatibility antigen .
• Every animal has its own histocompatibility antigen, which is inherited from its parents.
• The histocompatibility antigens vary in their ability to provoke immune response, some are not significant while others are potent to evoke immune response or rejection of graft.
• These potent antigens are inherited from parent through a set of genes known as major histocompatibility complex(MHC).
• MHC is an organized cluster of genes that control antigen processing and presentation. They are found in multiple systems.
• Immunological response to antigens are controlled by specific genes called immune response (Ir) genes, which are believed to be located in the HLA class-II region, probably in the DR Locus.
• All vertebrate animals have MHC genes that are maintained as linked genes. But the arrangements of genes differ with species.
• The genes are labeled A, B, C and D and they are co-dominant.
• Only one gene of each pair can code for antigen in a given individual and these antigens are different form one individual to others. Collectively the genes of
  • Human MHC are called HLA (Human leukocyte antigen)
  • Cattle - BOLA (Bovine leukocyte antigen)
  • Sheep – OLA (Ovine leukocyte antigen)
  • Horse – ELA (Equine leukocyte antigen)
  • Swine –SLA (Swine leukocyte antigen)
  • Dog- DLA (dog leukocyte antigen),
  • Mouse – H₂ (Histocompability),
  • Chicken – B
• MHC plays an important role in recognition of protein antigens by T cells. T cells do not recognize free soluble antigens but recognize peptide antigens that are non-covalently bound to MHC molecules, i.e. either Class I or Class II molecules.