The mechanism by which foreign antigens are taken into antigen-presenting cells (APCs) and broken up. Part of the antigen is then displayed (presented) on the surface of the APC next to a histocompatibility or “self” antigen, activating T lymphocytes and cell-mediated immunity. T lymphocytes are unable to recognize or respond to most antigens without APC assistance.

See: antigen; macrophage processing; self