CD300a protein is a member of the CD300 glycoprotein family, which are type I transmembrane proteins expressed on the surface of various leukocytes. It has an IgV-like extracellular domain and a long cytoplasmic tail containing immunoreceptor tyrosine-based inhibitory motifs (ITIMs), which are crucial for its inhibitory signaling. CD300a is expressed in natural killer (NK) cells, subsets of T and B cells, monocytes, dendritic cells, granulocytes, and mast cells. It plays an inhibitory role in immune responses by regulating various functions such as inhibiting Ca++ mobilization in response to receptor stimulation, suppressing NK cell-mediated cytotoxicity, B-cell proliferation, and mast cell activation. Additionally, CD300a mediates immune tolerance to dying cells by binding to phosphatidylserine and phosphatidylethanolamine. Its expression and function are regulated by various cytokines and stimuli, and it has potential implications in allergic diseases and other immune-related conditions.