Description
CD160 (also Natural killer cell receptor BY55) is a 16kD (predicted) member of the Ig superfamily (1-4). In mouse, it is expressed principally on nonmyeloid hematopoietic cells. These include CD3+ NK1.1 cells, CD8+ TEM and TCM T cells, CD8a+ IELs, NKT cells, CD8-yd TCR T cells, and vascular endothelial cells (1, 5-7). Mouse CD160 has been identified as a 20-21kD GPI-linked glycoprotein (4, 5). It is synthesized as a preproprotein that is 185aa in length. The precursor contains a 27 aa signal sequence, a 133 aa mature molecule that shows one 98 aa V-type Ig-like domain (aa 28-125), and a 25 aa prosegment that is cleaved to generate a GPI-linkage at Ser160. Mouse GPI-linked CD160 is known to be cleaved by phospholipase C, and this generates a 40kD (presumably dimeric) band in SDS-PAGE (5). One alternative splice form for mouse CD160 is reported that appears to show a deletion of aa 137 - 180. This may generate a soluble molecule (5; GenBank Accession # NP_001156969). Mature mouse CD160 shares 63% and 88% aa identity with human and rat CD160, respectively. In mouse, CD160 is reported to bind to bind to HVEM/TNFRSF14, and both classical and non-classical MHC Class I molecules (5, 8). MHC-I proteins recognized by CD160 include Dd, Kb, Qa-1b and CD1d (5). Upon engagement, the effects of CD160 ligation appear to be context dependent. When expressed on endothelial cells, CD160 binding to human HLA-G1 initiates apoptosis, and thus impacts angiogenesis (6). When expressed on NK1.1 cells, mouse CD160 ligation alone has no effect; when combined with NK1.1 antigen stimulation, CD160 decreases NK cell IFN-y secretion. Relative to cytotoxicity, NK cell activity is positively correlated with the presence of CD160 (5)