Allergin-1, also known as mast cell Ag-32, is a 60 kD single pass transmembrane protein. It contains one Ig-like C2-type (immunoglobulin-like) domain in the extracellular region and one immunoreceptor tyrosine-based inhibitory motif (ITIM)-like domain in the cytoplasmic region. Allergin-1 is expressed on mast cells, dendritic cells, and macrophages as well as at low levels on neutrophils. After tyrosine phosphorylation, allergin-1 recruits PTPN6, PTPN11, and INPP5D, which results in a diminution of IgE-mediated degranulation in mast cells. No ligands have been identified for this molecule.