THIOL-PROTEINDISULFIDE-OXIDOREDUCTASE (PROTEINDISULFIDE ISOMERASE) - A NEW PLASMA-MEMBRANE CONSTITUENT OF MATURE HUMAN B-LYMPHOCYTES

The thiol-proteindisulfide-oxidoreductase (TPO, EC 1.8.4.2., proteindi sulfide isomerase, EC 5.3.4.1.) is known as an cytoplasmatic enzyme, a nd is thought to be involved in the post-translational folding of disu lfide containing proteins. Using monoclonal and polyclonal antibodies the authors were able to prove that this enzyme or an unknown homologo us protein is localized also to the plasma membrane of B lymphocytes. In peripheral blood from healthy donors 11% of the mononuclear cells ( PBMNC) expressed this surface antigen whereas in PBMNC of patients wit h B-cell chronic lymphocytic leukaemia 76% of the MNC were positive. T his value correlates well with the known B-cell markers CD19 and CD20. However, this antigen is different from all known clustered B-cell ma rkers. Immunoprecipitation analysis of PHA-stimulated PBMNC and of cel ls from patients suffering from chronic lymphocytic leukaemia revealed a membrane protein with the same molecular weight (61 kDa) as the TPO . These data suggest that this enzyme is present not only in the cytop lasm but also on the surface of B cells and that it is possibly involv ed in the regulation of the SH-SS status of the cell membrane proteins of B lymphocytes.