Cell-mediated immunity

Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

The most important of these APCs are highly specialized dendritic cells; conceivably operating solely to ingest and present antigens.

It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria.

Type 1 immunity is directed primarily at viruses, bacteria, and protozoa and is responsible for activating macrophages, turning them into potent effector cells.

CD8+ cytotoxic T-cells may also be categorized as:[5] Similarly to CD4+ TH cells, a third category called TC17 were discovered that also secrete IL-17.

By secreting interferon gamma and TNF, TH1, TC1, and group 1 ILCS activate macrophages, converting them to potent effector cells.

TH1 cells are also characterized by the expression of chemokine receptors which allow their movement to sites of inflammation.

Additionally, interferon gamma secreted by these cells seems to be important in downregulating tight junctions in the epithelial barrier.

Immunofluorescence micrograph of three cytotoxic T cells (outer three) surrounding a cancer cell. Lytic granules (red) are secreted at the contact site, killing the target. Cytotoxic T cells are powerful agents of cellular immunity.