CD45 Background Information
CD45 is characterized as a transmembrane glycoprotein, broadly expressed among hematopoietic cells (1,2). Eight isoforms of CD45 are distributed throughout the immune system according to cell type (1). These isoforms consist of a distinct extracellular domain, while the intracellular domain is conserved (1,3). CD45 functions as a phosphotyrosine phosphatase, a vital component for efficient tyrosine phosphorylation induced by the TCR/CD3 complex (4–7). The tyrosine phosphatase activity of CD45 is contained within the conserved intracellular domain and is thought to be regulated by phosphorylation on mulptiple residues, including Ser-940 (3,8). Src and Syk family protein tyrosine kinases are utilized by the TCR/CD3 complex to initiate signaling cascades (6). Several members of these two families, including Lck, Fyn and Zap70, have been implicated as physiological substrates of CD45 (6,9).
