CD45 is a 180-240 kD glycoprotein, also known as the leukocyte common antigen (LCA), T200, or Ly-5. As a member of the protein tyrosine phosphatase (PTP) family, it is expressed on all hematopoietic cells except mature erythrocytes and platelets. Different isoforms of CD45 are generated through the alternative splicing of exons 4, 5, and 6, which encode the A, B, and C determinant regions, respectively. CD45 plays a critical role in the signal transduction of both the T-cell receptor (TCR) and B-cell receptor (BCR). These isoforms exhibit high specificity for the cell's activation and maturation status, as well as the cell type. Key ligands for CD45 include galectin-1, CD2, CD3, TCR, CD4, CD22, and Thy-1.
