Activated cells that execute a specific immune response.
On the one hand, this refers to T cells that have previously been sensitized by an antigen and then have a cytotoxic effect on the target cell containing the antigen.
For example, the tumor cells of mycosis fungoides are identified as CD4+ skin-resident effector memory T cells (Trm cells) of clonal origin. They are part of the local immune defense of the skin, are long-lived and stably committed to their home tissue, which makes the often decades-long exclusive skin infestation plausible (DeSimone JA et al. 2015).
For B cells, the antibody-forming plasma cells or the antibodies themselves are the effectors.
Natural killer cells(NK cells) recognize or destroy degenerated or infected cells without prior sensitization.