Veterinary Immunology and Serology

TYPES ACCORDING TO ANTIGENIC SPECIFICITY

Species-specific antigen

• An antigen is specific in relation to a specific species of host only.

Organ specific antigen

• The antigen is specific in relation to a particular organ in a single species. For example, kidney protein is different from lung protein.

Heterophile antigens

• They are antigens of identical nature present in the cells of some bacterial species and also in the tissues of different animals. Antibody formed against one antigen cross-react with other antigens. There is a phenomenon of antigenic sharing.
• Examples:
  • Frossman antigens are a group of related heterophile antigens. They are present in the cell wall of many bacterial species (glycoprotein with carbohydrate side chain) belong to the genera streptococcus, shigella, salmonella and clostridium and also on the surface of red blood cells (glycoprotein) of horses, sheep, cats and mice. The animals having Frossman antigens in their tissues do not develop antibodies because the antigens are considered as ‘self’
  • A heterophile antigen is found in some proteus strains (OX-19, OX -2, OX-K) and also certain Rickettsial organisms (e.g. Rickettsia rickettsii). This forms the basis of Weil-Felix reaction. An agglutination test is used to detect antibody in human beings against Rickettisal organisms using Proteus antigen.

Alloantigens (isoantigens)

• These are antigens present in one individual and are antigenic to some individuals of the same species. The corresponding antibodies are called alloantibodies. Example: Blood group antigen, Transplantation antigen etc.

Syngenic antigen

•  The antigens present in the individuals of the same genetic make up. Example- antigens present in monozygotic twins.

Autoantigen

• In certain circumstances, own body tissues develop antigenic properties and antibody formed against the antigen. The auto antigens are sequestrated without contact with the lympho-reticular system but by any mishap when antigens are released, they provide an opportunity to produce autoantibody. Example: sperm, lens protein etc.

 Super antigen

• A group of molecules that do not have to be processed by antigen presenting cells in order to activate T cells. Examples – Bacterial antigens (Streptococcal A antigen).