The CD300, alternately designated the LMIR family, contains six to eight type I membrane proteins expressed mainly on cells of the myeloid lineage. Each has a single extracellular V-type Ig-like domain. Some have cytoplasmic ITIM motifs that result in the delivery of an inhibitory signal; others can interact with ITAM motifs and function as activating receptors. Human CD300 proteins have also been designated IREM (immune receptor expressed by myeloid cells) or CMRF-35 for the original identifying antibody; mouse CD300 proteins have alternate naming as CLM (CMRF-35-like molecules).