Cell surface receptor that may play a role in the innate and adaptive immune response. When phosphorylated, interacts with PTPN11 (By similarity). When phosphorylated, interacts with PTPN6. Sequestered in cytoplasmic vesicles in resting platelets. Transported to the cell surface after stimulation by thrombin. Soluble fragments can be released into the serum by proteolysis. Highly expressed in bone marrow leukocytes, splenic megakaryocytes and platelets. Detected in brain, liver and in peritoneal monocytes. Phosphorylated on tyrosine residues.