http://www.creativebiomart.net/description_382817_12.htm

B220, also known as CD45 and PTPRC, is a member of the protein tyrosine phosphatase (PTP) family. PTPs regulate a variety of cellular processes including cell growth, differentiation, mitotic cycle, and oncogenic transformation. B220 is expressed in lymphomas, B-cell chronic lymphocytic leukemia, hairy cell leukemia, and acute nonlymphocytic leukemia.B220 is a receptor type PTP since it contains an extracellular domain, a single transmembrane segment and two tandem intracytoplasmic catalytic domains. B220 is an essential regulator of T- and B-cell antigen receptor signaling. It functions through either direct interaction with components of the antigen receptor complexes or by activating various Src family kinases required for the antigen receptor signaling. B220 also suppresses JAK kinases, and, thus, functions as a negative regulator of cytokine receptor signaling.