CD45, previously called LCA (leukocyte common antigen), T200, or Ly5 in mice, is member C of the class 1 (receptor‑like) protein tyrosine phosphatase family (PTPRC). It is a variably glycosylated 180-220 kDa transmembrane protein that is abundantly expressed on all nucleated cells of hematopoietic origin . Multiple splicing isoforms of exon 4 (A), 5 (B), and 6 (C) are expressed according to cell type, developmental stage and antigenic exposure . The longest form, CD45RABC (called B220 in mouse) is expressed on B lymphocytes, The shortest form, CD45R0, lacking exons 4, 5 and 6 which encode aa 34‑194, is expressed on memory cells, while intermediate sizes are expressed on other T cells.