Cell-mediated immunity typically comes into play at body sites where cells are infected by a virus, bacteria, or fungi (intracellular invaders). With the assistance of MHC class I proteins, T cells can also recognize cancerous cells.

What triggers cell-mediated immunity?

Cell-mediated immunity is primarily driven by mature T cells, macrophages, and the release of cytokines in response to an antigen. T cells involved in cell-mediated immunity rely on antigen-presenting cells that contain membrane-bound MHC class I proteins in order to recognize intracellular target antigens.

Where does cell-mediated immunity occur?

Cellular immunity occurs inside infected cells and is mediated by T lymphocytes. The pathogen's antigens are expressed on the cell surface or on an antigen-presenting cell.