Type II Hypersensitivity Reaction and Related Disorders in Animals

Rathor C and Chauhan RS (2020). Type II Hypersensitivity Reaction and Related Disorders in Animals. Journal of Immunology Immunopathology, 22(1): 35-47.

Antibody binding to the cell surface antigen causes destruction of cells through a mechanism called type II hypersensitivity. In the Gell-Coombs formulation, type II hypersensitivity reactions are characterized by antigen- antibody interactions, resulting in the local production of anaphylotoxin (C5a), the recruitment of polymorphonuclear leukocytes (PMNs) and subsequent tissue injury due to the release of hydrolytic neutrophil enzymes after their autolysis. Incompatible blood transfusion and hemolytic diseases are the best examples for the type II hypersensitivity reaction. In transfusion reactions, the antibodies present in the recipient blood destroy the red blood cells of the donor. The antigens found on the surface of erythrocytes are known as blood group antigens. Glycophorin is one of the more common RBC membrane antigens, which is targeted by auto-antibodies that spans over the plasma membrane. The specifications on the erythrocyte, which react with the different reagent or antisera are called as antigenic factors or blood factors. Blood factors are determined by genes at the same locus which belong to the same blood group system. Erythrocytes of man and animals are provided with the different blood group antigens. They vary among different species with regard to their structure, antigenicity and complexity. Some blood group antigen such as ‘B’ system in cattle and ‘A’ antigen in cats are more important from a clinical point of view and are widely distributed in the population. The immune mediated destruction of circulating red blood cells (RBC) occurs by two different mechanisms i.e. by the intravascular destruction of erythrocyte by complement lysis, which is initiated by antibodies that are often of IgM class. The second mechanism is extravascular destruction by immune cells, which identify IgG and complement bound to erythrocytes. Hemolytic syndrome includes immune mediated hemolytic anemia, autoimmune hemolytic anemia, alloimmune (transfusion) hemolytic anemia and drug-induced hemolytic anemia. The Immune-mediated hemolysis occurs due to anti-erythrocyte antibodies, secondary to malignancies, autoimmune disorders, some drugs, and transfusion reactions. A hybrid foetus of sheep and goat dies due to haemolytic anemia when antibodies to their own red blood cells cross the placenta from the maternal circulation. Other transfusion hazards like acute and delayed transfusion reactions, transfusion-related acute lung injury (TRALI), graft-versus-host disease (GVHD), transfusion-associated graft-versus-host disease (TA-GVHD), transfusion-induced immunomodulation and lower nephron nephrosis also occurs in animals. These hazards are infectious and noninfectious in origin.