May act as receptor for class I MHC antigens. Becomes activated upon coligation of LILRB3 and immune receptors, such as FCGR2B and the B-cell receptor. Down-regulates antigen-induced B-cell activation by recruiting phosphatases to its immunoreceptor tyrosine-based inhibitor motifs (ITIM). Interacts with LYN, PTPN6/SHP-1 and PTPN11/SHP-2. Detected in monocytes and B-cells. Contains 3 copies of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). This motif is involved in modulation of cellular responses. The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases, including PTPN6/SHP-1, resulting in the dephosphorylation of the downstream protein kinases SYK and BTK. Phosphorylated on tyrosine residues by LYN. Phosphorylation at Tyr-595 and Tyr-625 is important for interaction with PTPN6/SHP-1 and PTPN11/SHP-2. Belongs to the leukocyte receptor cluster (LRC) present on 19q13.4.