36.1 Delayed type hypersensitivity (DTH)

These types of reaction are caused by stimulation of CD4+ T cells and are mediated by cytokines. It is called delayed as it evolves 24 to 48 hrs after antigen reaction. In classical form of DTH, a guinea pig is first sensitized with the antigen and after 14 days challenged with the same antigen subcutaneously, the subsequent reaction is then analyzed in the elicitation reaction. In humans, most famous model is the injection of purified protein derivative (PPD) of Mycobacterium tuberculosis that elicits a DTH response in an individual who has been previously exposed to M. tuberculosis (tuberculin reaction).

Figure 36.1 Schematic representation of delayed type hypersensitivity reaction: