SIRP alpha/CD172a

SIRP alpha, the CD172a antigen, is the prototypic signal regulatory protein, an inhibitory receptor whose cytoplasmic region carries ITIM motifs that recruit SHP phosphatases upon phosphorylation. Its extracellular IgV-like domain binds CD47, forming the CD47-SIRPalpha axis through which the widely expressed don't-eat-me signal prevents phagocytosis of healthy self cells. The receptor is expressed on myeloid cells, including macrophages and dendritic cells, and on neurons. Because many tumors amplify CD47 expression to evade macrophage clearance, disruption of the interaction with SIRP alpha, alone or combined with tumor antibodies, has become a prominent strategy in myeloid-directed cancer immunotherapy.