Cell-mediated immunity involves T lymphocytes and macrophages responding to antigens inside cells. It activates cytotoxic T cells to induce apoptosis in infected cells, and activates macrophages and natural killer cells to destroy intracellular pathogens. T cell activation requires two signals - antigen presentation via MHC and co-stimulation from antigen presenting cells like dendritic cells, macrophages, and B cells. Once activated, T cells differentiate into effector T cells that eliminate pathogens through cytotoxic killing or cytokine signaling.

1. Cell-mediated immunity