LMIR5, also known as CD300LB, CLM-7, and IREM-3, is a 26kD-32kD glycoprotein member of the immunoglobulin superfamily. Mouse LMIR5 consists of a 140aa extracellular domain (ECD) with one Ig-like V-type domain, a 21aa transmembrane segment, and a 31aa cytoplasmic domain. Within the ECD, mouse LMIR5 shares 51% and 86% aa sequence identity with human and rat LMIR5, respectively. The transmembrane segment contains a positively charged lysine which enables the association of LMIR5 with DAP12, DAP10, and potentially other adaptor proteins. The cytoplasmic domain of human LMIR5 contains a phosphorylatable tyrosine motif, while that of mouse LMIR5 does not. LMIR5 is expressed on the surface of myeloid lineage cells. It forms noncovalent cis-homodimers and cis-heterodimers with other CD300 family proteins, and the composition of these dimers affects the cellular response. Antibody cross-linking of LMIR5 induces mast cell granule release and cytokine production as well as its tyrosine phosphorylation of LMIR5 (in human). LMIR5 interacts with TIM1 and TIM4 which regulate T cell activation and are themselves binding partners. TIM1 interactions with LMIR5 mediate mast cell activation and the accumulation of neutrophils at sites of TIM1 up-regulation on damaged renal tubule epithelial cells.