Cell surface receptor that may play a role in the innate and adaptive immune response. When phosphorylated, interacts with PTPN6 (By similarity). When phosphorylated, interacts with PTPN11. Sequestered in cytoplasmic vesicles in resting platelets (PubMed:15100151). Transported to the cell surface after stimulation by thrombin (PubMed:15100151). Soluble fragments can be released into the serum by proteolysis (PubMed:16505478). Detected in platelets, monocytic leukemia and in T-cell leukemia. Phosphorylated on tyrosine residues.