Signaling pathways engaged by NK cell receptors: double concerto for activating receptors, inhibitory receptors and NK cells

Despite the absence of antigen-specific receptors at their surface, NK cell s can selectively eliminate virus-infected cells, tumor cells and allogenic cells. A dynamic and Precisely coordinated balance between activating and inhibitory receptors governs NK cell activation programs. Multiple activati ng and inhibitory NK cell surface molecules have been described, a group of them acting as receptors for MHC class I molecules. In spite of their hete rogeneity, activating NK cell receptors present remarkable structural and f unctional homologies with T cell- and B cell-antigen receptors. Inhibitory NK cell receptors operate at early stages of activating cascades by recruit ing protein tyrosine phosphatases via intracytoplasmic motifs (ITIM), a str ategy which is widely conserved in hematopoietic and non-hematopoietic cell s. (C) 2000 Academic Press.