LMIR1, also termed CD300a, is a type I transmembrane glycoprotein with a single IgV-like extracellular domain and an extended membrane proximal region that links the immunoglobulin (Ig) and transmembrane domains and belongs to the immunoglobulin superfamily. The intracellular domain of LMIR1 contains several immunoreceptor tyrosine-based inhibition motifs (ITIMs). When cross-linked, it will be tyrosine phosphorylated and capable of recruiting tyrosine phosphatases (SHP-1, SHP-2) and inositol polyphosphate 5-phosphatase, SHIP. LMIR1 will regulate mast cell-mediated inflammatory responses. LMIR1 is broadly expressed on myeloid and lymphoid cells, and its expression is differentially regulated depending on the cell type.