Changes

Cell mediated hypersensitivity:

Cell mediated hypersensitivity:

Exposure to antigen causes CD4+ T helper cells to be activated leading to colonal expansion (takes 1-2 weeks). On subsiquent exposure with the same antigen sensitised CD4+ T helper cells secrete cytokines which attract and activate macrophages. The macrophages have an increased ability to phagocytose pathogens, which is very important for the clearance of intracellular pathogens. However if antigen persists, the lytic products of the macrophages can damage healthy tissues.

Type IV hypersensitivity involves cytokines being secreted from the Th-I cells, which cause the activation of macrophages and other T cells.

 

Involves TH-1 releasing cytokines which activate macrophages and other T cells.

* CD4+ T cell mediated:

* CD4+ T cell mediated:

* CD8+ T cell mediated:

* CD8+ T cell mediated:

** Cytotoxic T lymphocytes (CTLs) kill healthy cells mistakenly thinking they are infected by a virus.

** Cytotoxic T lymphocytes (CTLs) kill healthy cells mistakenly thinking they are infected by a virus.

==3 types:==

==3 types:==