DEGRADATION OF GLYCOPHORIN-A OF HUMAN ERYTHROCYTES IN PATIENTS WITH MYELOPROLIFERATIVE OR LYMPHOPROLIFERATIVE DISORDERS - POSSIBLE ROLE OF NEUTROPHIL PROTEASES

We have previously reported that glycophorin A (GPA) of human erythroc ytes (carrying blood group M and N determinants) was totally digested by incubation of erythrocytes with human neutrophil elastase (HNE) and cathepsin G (CathG). The membrane-bound GPA fragments fractionated by SDS-PAGE gave characteristic patterns of bands detected by immunoblot ting with the monoclonal antibody PEP80. Erythrocytes were incubated w ith HNE and CathG at low enzyme concentrations, similar to those found in vivo. Characteristic electrophoretic patterns of bands derived fro m a partial GPA digestion were observed and these patterns were differ ent for both enzymes and different from those obtained after total GPA digestion. GPA was also partially digested by incubation of erythrocy tes with granulocytes in the presence of Ca2+ and calcium ionophore an d electrophoretic pattern of digestion products was similar to that ob tained with low doses of HNE. No GPA digestion products were detected after treatment of erythrocytes with plasmin and kallikrein. Untreated erythrocytes of 21 patients with various myelo- or lymphoproliferativ e disorders were tested by SDS-PAGE of RBC membranes and immunoblottin g with the anti-GPA PEP80 antibody, GPA degradation products, resembli ng those formed by a mild CathG treatment of control RBC, were detecte d in nine patients. GPA fragmentation was in some cases accompanied by a reduced expression of blood group MN determinants. No distinct rela tion was observed between the occurrence of GPA degradation in erythro cytes and increases in plasma concentrations of HNE-alpha(1)-proteinas e inhibitor (alpha(1)-PI) complex considered to be an indication of a release of neutrophil proteinases in vivo. However, the results sugges ted that a partial GPA degradation in haematological proliferative dis orders may occur due to limited proteolysis by neutrophil proteinases, most likely by CathG.