Signal regulatory protein α (SIRPα) is a regulatory membrane glycoprotein from SIRP family expressed mainly by myeloid cells and also by stem cells or neurons.SIRPα acts as inhibitory receptor and interacts with a broadly expressed transmembrane protein CD47 also called the "don′t eat me" signal.Cancer cells highly expressed CD47 that activate SIRP α and inhibit macrophage-mediated destruction.