Paired Ig-like receptors of activating (PIR)-A and -B are expressed on B lymphocytes, macrophages, dendritic cells, platelets, granulocytes, and mast cells, but not on T cells, NK cells, and erythrocytes. These cell surface glycoproteins contain six extracellular Ig-like domains with distinct cytoplasmic and transmembrane regions. The PIR-A receptor activates through signaling molecules containing immunoreceptor tyrosine-based activation motifs. In contrast, the PIR-B receptor inhibits through proteins possessing immunoreceptor tyrosine-based inhibitory motifs. PIRs bind MHC class I to modulate immune system homeostasis and cell signaling.
Cell-surface glycoprotein p91; Gp49b; Leukocyte immunoglobulin-like receptor 3; Leukocyte immunoglobulin-like receptor subfamily B member 3; leukocyte immunoglobulin-like receptor, subfamily B (with TM and ITIM domains), member 3; Lilrb3; Lilrb4; LIR-3; Paired immunoglobulin-like receptor B; PIR-B; Pirb