Type IV Hypersensitivity Reaction and Its Associated Disorders in Animals

Deeksha and Chauhan RS (2020). Type IV Hypersensitivity Reaction and Its Associated Disorders in Animals. Journal of Immunology Immunopathology, 22(1): 56-65.

The major defence mechanism against intracellular pathogens like Mycobacterium, Brucella, fungi and certain parasites is delayed type of hypersensitivity. Delayed hypersensitive reaction is induced by cytokines, secreted by subpopulation of activated T cells during encountering with certain type of antigens. Delayed type hypersensitivity reaction is slower in onset and develops within 72 h and the response is prolonged. Sensitisation of the CD4+ cells of Th1 type occurs during its first exposure to an antigen. These sensitised Th1 cells remain in the circulation for a very long time. On subsequent exposure to the same antigen, sensitised Th1 cell release chemotactic factor for macrophages which leads to recruitment of macrophages at the site of infection. Various cytokines are also releases that lead to the tissue injury. Tissue damage is also mediated by CD8+ cells through direct toxicity. Delayed type hypersensitivity reaction also helps in the diagnosis and eradication programme of diseases caused by intracellular pathogen where cellular immunity plays an important role. Tuberculin reaction is one such example of the delayed type of hypersensitivity reaction. Allergic contact dermatitis is skin’s delayed-type hypersensitivity caused by the non-irritating agents like paint, cosmetics, collars, etc. these allergens are identified by the patch testing. Allograft rejection is also a T-cell-mediated response that makes organ transplantation unsuccessful.