Natural killer cell
type of cytotoxic lymphocyte / From Wikipedia, the free encyclopedia
Natural killer cells (or NK cells) are a type of lymphocyte critical to the innate immune system. NK cells provide a rapid response to cells infected by viruses, or to bacterial cells. The response happens about 3 days after infection. NK cells also respond to tumour formation.
NK cells are unique: they have the ability to recognise stressed cells in the absence of antibodies and major histocompatibility complex (MHC). This allows for a much faster immune reaction.[1]
In early experiments in cancer patients and animals, investigators found what was called a "natural" reactivity. That is, a certain population of cells seemed to be able to kill tumour cells without previously being sensitized to them. At first many thought that these observations were artifacts.[2] However, by 1973, 'natural killing' activity was established across a wide variety of species, and the existence of a separate line of cells with this ability was suggested.