Biochemical and antigenic characterization of CD45 polypeptides expressed on plasma membrane and internal granules of...

The expression of CD45 polypeptides, a phosphotyrosine phosphatase complex specific of leukocytes, has been investigated in both resting and activated neutrophils by using anti-CD45 monoclonal antibodies (MAb) which specifically recognize different polypeptide components of the CD45 molecular complex. Polypeptides of 180 and 130-150 kDa were equally precipitated by either a conventional CD45 MAb recognizing an antigenic determinant shared by the four CD45 glycoproteins (220, 205, 190 and 180 kDa) or by the anti-180 kDa UCHL1 MAb. These polypeptides were overexpressed on neutrophil plasma membranes after degranulatory stimulation. Conversely, neither the anti-220 kDa CD45R nor anti-220/205/190 kDa MAb reacted with CD45 molecules from resting or activated neutrophils. Furthermore, permeabilization analysis and comparative immunoprecipitation studies with different anti-CD45 MAb from fractions enriched in various neutrophil granules revealed that CD45 polypeptides (180 and 130-150 kDa) from internal granules are antigenic and biochemically identical to those expressed on plasma membrane.