White blood cells or lymphocytes that form part of the 'innate' immune system capable of recognising foreign cells and dissolving them (hence their name: natural killer cells). Found normally, however, in the endometrium of the late secretory phase and in the decidua of pregnancy, where they have more friendly purposes in forming the boundary between mother and fetus. Unlike T cells and B cells, most NK cells do not have 'immunological memory', whereby previous contact with a particular antigen causes a faster, more deadly immune response second time round.

Large lymphocytes that attack certain cells on contact and probably help regulate the immune system.

Natural Killer cells are a group of lymphocytes (not T or B cells) that can kill some virally infected and tumor cells.

Non-specific lymphocytes like killer T cells that attack and kill cancer and infected cells. They are natural killers because they do not need to recognize a specific antigen in order to attack and kill.

See natural killer cells.

a large lymphocyte that bonds to cells and destroys them. These cells are effective against cells infected with viruses and some type of tumor cells.

A group of lymphocytes which have the intrinsic ability to recognize and destroy some virally infected cells and some tumour cells.

Specialized cells of the immune system that kill bacteria, viruses, and other foreign substances in the body.