Isospecificity - Antigen

Isospecificity

Isospecificity is determined by the presence of isoantigens or histocompatibility antigens.

Isoantigens

Isoantigens are antigens found in some, but not all, members of a species. A species may be grouped depending on the pres-ence of different isoantigens in its members. These are geneti-cally determined. Human erythrocyte antigens, based on which individuals are classified into different blood groups, are the best examples of isoantigens in humans. The blood groups are of primary importance in:

·           Transfusion of blood and blood products,

·           Isoimmunization during pregnancy, and

·           Providing valuable evidence in paternity disputes, the results of which are supplemented by m ore recent DNA fingerprinting tests.

Histocompatibility Antigens

Histocompatibility antigens are the cellular determinants specific for each individual of a species. These antigens are associated with the plasma membrane of tissue cells. Human leukocyte antigen (HLA) is the major histocom-patibility antigen that determines the homograft rejection. Therefore, HLA typing is absolutely essential before carrying out transplantation of tissue or organ from one individual to another.