CD16 (Natural Killer Cells)

CD16 (FcγRIII) on NK cells binds the Fc portion of IgG on antibody-coated targets, triggering antibody-dependent cellular cytotoxicity (ADCC). Engagement induces ITAM-mediated signaling, NK cell activation, degranulation with perforin/granzymes release, and cytokine production (e.g., IFN‑γ), enabling killing of infected or tumor cells. CD16 is a low‑affinity Fc receptor; genetic variants influence its binding and ADCC potency.

NK cells segregate into CD56bright CD16−/dim and CD56dim CD16+ subsets. CD56bright CD16−/dim are mainly in lymphoid tissues, produce high levels of cytokines (e.g., IFN-γ), have lower direct cytotoxicity, and respond strongly to cytokines like IL-2. CD56dim CD16+ dominate blood, express perforin/granzyme, are highly cytotoxic and mediate antibody-dependent cellular cytotoxicity via CD16 (FcγRIIIa).

CD16 (FcγRIII) is an Fc gamma receptor expressed mainly on natural killer (NK) cells and on certain myeloid cells — neutrophils, monocytes and macrophages. It’s used as a marker to identify NK cells and mature neutrophils and reflects capacity for antibody-dependent cellular cytotoxicity (ADCC) and immune complex handling. Two isoforms exist: CD16a (NK cells, monocytes/macrophages) and CD16b (neutrophils).

Most canonical NKT cells (CD3+ CD1d-restricted invariant NKT) do not express CD16 (FcγRIII). They can share some NK receptors (e.g., CD56, NKG2D), but CD16 is typically absent or only present on rare/activated NKT-like subsets. Thus CD16 is not a defining marker for classical NKT cells; any CD16 positivity is variable and subset-dependent.

Natural killer (NK) cells are innate lymphocytes whose main function is to detect and rapidly eliminate virus‑infected and transformed (tumor) cells without prior sensitization. They kill targets by releasing cytotoxic granules (perforin and granzymes), mediate antibody‑dependent cellular cytotoxicity, and secrete cytokines like interferon‑gamma to shape and activate other immune responses.

CD16 (FcγRIII) is primarily expressed on natural killer cells, neutrophils and some monocytes, not on conventional T cells. However, small, highly differentiated CD8+ T‑cell subsets—and occasionally γδ T cells—can express CD16 after activation or during chronic infection. Those CD16+ T cells can mediate antibody‑dependent functions, but CD16 expression on T cells is uncommon and context‑dependent.