The cell-mediated response is part of the immune response against infection of cells.

T cells are responsible fo this response. They differentiate under the influence of the thymus and respond to bacteria and viruses within infected body cells, also cancer cells and transplanted tissues.

A macrophage engulfs a bacteria and antigens are stripped and put on receptors which are presented on the surface of the macrophage. This antigen is presented to a virgin T cell. The T cell receptor must recognize botht the MHC-II protein and the specific antigen fragment to bind.

A CD4 protein also helps secure the relationship between the macrophage and the T cell.

The T cell becomes activated and divides into helper T cells, cytotoxic T cells.
The helper T cells help activate B cells in the humoral response.

The T cells also secrete interleukins, some of which cause a fever or help differentiation of other T cells.

The cytotoxic T cells are the effectors of the cell-mediated response. They search and destroy infected cells by secreteing chemicals that punches holes in the infected cell's membrane, causing lysis.