CD45 is a family of single chain transmembrane glycoproteins, consisting of different isoforms, which share a common large intracellular domain. It is abundantly present in leukocyte cell surface and belongs to a novel class of enzymes, the protein tyrosine phosphatases (PTPs). It plays an essential role in thymic selection and peripheral activation of T and B cells. It is associated with various signal transduction pathways. It may also accelerate the Src family tyrosine kinases activity. an important determinant of immune tolerance.
