4AA9 reacts with CD45, a 180-220 kDa leukocyte common antigen (LCA). CD45 antigen is expressed at high levels on all hematopoietic cells including T and B lymphocytes, monocytes, granulocytes, NK cells and dendritic cells, but is not expressed on non-hematopoietic cells. CD45 antibody has also been reported to react weakly with mature blood erythrocytes and platelets. CD45 is a protein tyrosine phosphatase receptor that is critically important for T and B cell antigen receptor-mediated activation.
*Target of immunosuppresive antibody treatment.