[Granular cells of the hepatic capillary sinuses--receptors]

Pit cells or hepatic natural killer (NK) cells represent an organ-associated NK cell population. They are situated in liver sinusoids and exert high spontaneous cytotoxic activity against tumor cell lines and may act as a primary defense barrier to metastasing tumor cells and to virus infections. Pit cells express two types of receptors on their cell membrane. One type activates NK cell killing (NCR or natural cytotoxicity receptors, as NKp46, NKp44, NKp30, NKG2D) by recognizing ill-defined molecules on target cells. The second type of receptors inhibits the lytic pathway by recognition of self class I MHC molecules and are represented by KIR or killer cell Ig-like receptors, as KIR2D, CD94/NKG2. Pit cells express on their cell membrane and other type of molecules as CD2, CD54, CD11a/CD18 and are CD3 negative.