USA Surgery Today

Two of the main functions of T cells are (1) to provide cytotoxic activity against facultative intracellular pathogens (mycobacteria, fungi) and virally infected cells or tumor cells, and (2) to provide cytokines (Table 15-2) to help B cells make antibodies.

For the T cell to carry out these functions, it first must bind to the target cell or to the antigen-presenting cell (APC), respectively. For high-affinity binding of T cells to target cells or APCs, several molecules on T cells in addition to TCRs bind to molecules on their respective target cells (Fig. 15-2).