The SIRP family of proteins consists of five members; SIRPα, SIRPß1, SIRPß2, SIRPγ and SIRPδ. Two of these, SIRPα (also known as PTPNS1, SHPS1, CD172A and P84) and SIRPγ (also known as CD172b), are known to bind CD47. SIRPα contains an extracellular region with three immunoglobulin superfamily (IgSF) domains, including a NH2-terminal ligand binding V-domain. SIRPα is expressed on all myeloid cell types, including monocytes, macrophages, neutrophils, a subset of dendritic cells and microglia. In addition, SIRPα expression has also been observed in brain tissue, and on a subset of CD8+ T cells during chronic infection.