CD45 (leukocyte common antigen, PTPRC) is a transmembrane protein tyrosine phosphatase that is widely expressed on the surface of all nucleated hematopoietic cells (T cells, B cells, NK cells, etc.). Its core functions include: regulation of immune cell ctivation: By dephosphorylating the inhibitory sites of Src kinases (such as Lck and Fyn), it activates the T-cell receptor (TCR) and B-cell receptor (BCR) signaling pathways. Maintenance of immune tolerance: Regulating thymocyte development and the clearance of autoreactive lymphocytes.
