Natural Killer Cell
- Natural Killer (NK) Cells are a type of lymphocyte which do not possess any antigen-specific receptors. Instead, these cells appear to detect surface markers on cells which indicate immunologically irregular behavior.
- NK Cells do not possess any type of antigen-specific receptor and instead recognize their cellular targets through poorly understood mechanisms. These leukocytes play important roles in killing of virus-infected cells and tumor cells. Certain virus infected cells may down-regulate surface expression of MHC molecules in an attempt to evade development of an Adaptive Immune Response. The absence of MHC expression is likely one mechanism by which NK Cells recognize cells infected with particular viruses.
- NK Cells develop from Hematopoietic Stem Cells in the bone marrow and progress through a Lympocyte progenitor stage which can give rise to B-cells or T-cells. A fuller description of this process is provided in Hematopoiesis.
- NK Cells, like all lymphocytes possess a large, unlobulated nucleus, justifying their classification as Mononuclear Cells. The nuclei of lymphocytes generally takes up the majority of the cell and thus they possess little in the way of cytoplasm.