The human natural cytotoxicity receptors (NCR) that induce HLA class I-independent NK cell triggering

The cytolytic activity mediated by human natural killer (NK) cells is the r esult of a balance between signals delivered by inhibitory and activating r eceptors. The inhibitory receptors are represented by different families of HLA-specific receptors characterized by immunoreceptor tyrosine-based inhi biting motif (ITIM) sequences in their cytoplasmic portion. The funct ion a nd the specificity of the inhibitory receptors imply the existence of trigg ering receptors specific for non-HLA ligands that are responsible far the i nduction of the cytolytic activity against HLA class I-deficient target cel ls. These receptors have remained elusive until recently when three distinc t NK-specific molecules, termed natural cytotoxicity receptors (NCR), were identified and cloned. The different members of this novel family of recept ors play a complementary role in the recognition and lysis of target cells. The NCR family is composed by a heterogeneous group of molecules belonging to the Ig superfamily that associate to different immunoreceptor tyrosine- based activating motif (ITAM)-containing signal transducing polypeptides. H uman Immunology, 61, 1-6 (2000). (C) American Society for Histocompatibilit y and Immunogenetics, 2000. Published by Elsevier Science Inc.