killer cell Either of two types of lymphocyte that destroy infected or cancerous host cells. Natural killer cells are distinct from both T cells and B cells in that they act without stimulation by a specific antigen. They attack cancerous and virus-infected cells that lack the normal class I histocompatibility proteins on their surface. This contrasts with the other type of killer cells – cytotoxic T cells – which require the presence on the surface of the target cell of foreign antigen combined with host histocompatibility proteins. Killer cells destroy their target cells by releasing proteins (perforins) that create pores through the target plasma membrane, thus causing lysis and cell death.

kill·er cell • n. Physiol. a white blood cell (a type of lymphocyte) that destroys infected or cancerous cells.

killer cell (kil-er) n. see natural killer cell.