Signal Regulatory Protein alpha (SIRP alpha) is a monomeric approximately 90 kD type I transmembrane glycoprotein. The 504 amino acid human SIRP alpha contains two Ig-like C1-type domains and one Ig-like V-type domain. SIRP alpha can express in various tissues, mainly on brain and myeloid cells, including macrophages, neutrophils, dendritic and Langerhans cells. It also can detect in neurons, smooth muscle and endothelial cells. SIRPA is an immunoglobulin-like cell surface receptor for CD47. SIRP alpha acts as docking protein and induces translocation of PTPN6, PTPN11 and other binding partners from the cytosol to the plasma membrane. SIRP alpha shows adhesion of cerebellar neurons, neurite outgrowth and glial cell attachment. SIRP alpha engagement generally produces a negative regulatory signal; it may mediate negative regulation of phagocytosis, mast cell activation and dendritic cell activation