SIRPs (signal-regulatory proteins) are a family of transmembrane glycoproteins that belong to Ig superfamily. SIRPa (CD172a, SIRPb),(SIRPb1,CD172b), and SIRPg (SIRPb2,CD172g) have been described. CD172a/b molecules are expressed on myeloid cells and neurons. CD172a serves as a substrate of activated receptor tyrosine kinases (RTKs). The interaction of CD172a intracellular domain with SHP-1 and SHP-2 displays negative signaling in the regulation of leukocyte adhesion and transmigration. CD47 (IAP) is an extracellular ligand for CD172a. CD172b is a disulfide-linked homodimer. CD172b has been shown to regulate neutrophil transepithelial migration through the interaction with DAP12 and Syk kinase (through TYROBP).