Cell-Mediated Immunity

A pathogen may change the cells of an organism upon infection or the cell could be changed by mutation as in the case of cancer cells.In both cases the cells need to be destroyed and the cell debris cleared quickly and effectively.Macrophages engulf and digest pathogens by phagocytosis. They then process antigens from the pathogen, combine them with the major histocompatibility complex and present the antigens at the surface of the cell.When T helper cells come into contact with these antigen-presenting cells, if any of the receptors on their cell surface are complementary to the antigens, the receptors bind to the antigens.This binding activates the T helper cells which produces interleukins that stimulate more T cells to divide rapidly by mitosis and form clones of the activated T helper cell.Interleukins also:  - stimulate B cells to divide:  - stimulate phagocytosis:stimulate the development of antigen-specific T killer cellsSome of the T helper cells develop into T memory cells.