CD172a, also known as SIRPα, is a type I transmembrane protein featuring an extracellular region with one V-set Ig-like domain and two C-set Ig-like domains, and a cytoplasmic tail containing two immunoreceptor tyrosine-based inhibition motifs (ITIMs) and a proline-rich region. It is expressed by monocytes, macrophages, myeloid cells, and neuronal tissues. Phosphorylation of the SIRPα ITIMs induces the recruitment and activation of the tyrosine phosphatases PTPN6 (SHP-1) and PTPN11 (SHP-2), leading to the negative regulation of various biological processes. The known ligands for CD172a include CD47, surfactant protein A (SP-A), and surfactant protein D (SP-D).
