Application of the proteolytic enzyme papain in routine platelet serology

The use of proteolytic enzymes is well established in red cell serology. These enzymes modify some antigen structures and remove sialic acid from the red cell membrane. Enzyme-sensitive structures have also been identified on the platelet membrane. The effect of papain, a proteolytic enzyme used widely in red cell serology, on the detection of various platelet alloantibodies was examined to determine its usefulness in platelet serology. Antisera with the specificities anti-HPA-la, -2b, -3a, -4a, -5a, -5b, and -Naka were examined. HLA antibodies were also included. All sera were tested by a solid-phase red cell adherence technique in parallel with untreated platelets (UP) and platelets treated with papain (PP) for 15 minutes at 37 degrees C. The reactivity of anti-HPA-2b was eliminated and that of anti-HPA-3a was either eliminated or almost eliminated with PP. Antisera specific for the other alloantigens tested reacted similarly or more strongly with PP compared with UP. These findings were confirmed by flow cytometry. The reactivity of HLA antibodies with PP was generally enhanced. Inactivation by papain of platelet alloantigens in the HPA-2 and HPA-3 systems, but not in other systems, may assist in resolving mixtures of platelet alloantibodies. Also, detection of weak antibodies of other specificities may be enhanced. The use of PP may be a simple and useful serologic tool for investigating platelet alloantibodies.