Enables several functions, including heparan sulfate proteoglycan binding activity; heparin binding activity; and protein tyrosine phosphatase activity. Involved in several processes, including lymphocyte differentiation; positive regulation of macromolecule metabolic process; and regulation of signal transduction. Acts upstream of or within several processes, including lymphocyte differentiation; positive regulation of lymphocyte activation; and regulation of protein phosphorylation. Located in external side of plasma membrane; focal adhesion; and membrane raft. Is expressed in several structures, including 3rd branchial arch; alimentary system; cardiovascular system; hemolymphoid system; and placenta. Used to study systemic lupus erythematosus. Human ortholog(s) of this gene implicated in hepatitis C; multiple sclerosis; severe combined immunodeficiency; and severe combined immunodeficiency, autosomal recessive, T cell-negative, B cell-positive, Nk cell-positive. Orthologous to human PTPRC (protein tyrosine phosphatase receptor type C).