PRESENCE OF IMMUNOGLOBULINS, C3 AND CYTOLYTIC C5B-9 COMPLEMENT COMPONENTS ON THE SURFACE OF ERYTHROCYTES FROM PATIENTS WITH BETA-THALASSAEMIA HBE DISEASE/

The occurrence of IgG, IgM, IgA, C3 and C5b-9 complement complexes on erythrocytes from 43 patients with beta-thalassaemia HbE disease was i nvestigated, Indirect immunoradiometric assays using radioiodinated pr otein A were employed to quantify the individual components. We confir med that circulating erythrocytes from thalassaemic patients contained elevated amounts of IgG, and small but significant amounts of C3, In addition, small but significant amounts of C5b-9 were detected, Levels of cell-bound IgG, C3 and C5b-9 were higher in splenectomized versus nonsplenectomized patients. The presence of C5b-9 on circulating cells from five splenectomized patients was confirmed by an ELISA employing a monoclonal antibody specific for a C5b-9 neoantigen. When C5b-9 pos itive cells from two patients were solubilized with detergent and subj ected to sucrose density gradient centrifugation, the terminal complex es sedimented as 25-40S macromolecules, thus behaving as membrane C5b- 9 complexes. The presence of C8 and C9 in these high molecular weight fractions was directly demonstrated by Western blotting. These results constitute the first demonstration that circulating diseased erythroc ytes may carry low numbers of potentially cytolytic C5b-9 complement c omplexes which may be partly responsible for the known ionic disturban ces found in thalassaemic cells. Both bound C3 and C5b-9 could promote removal of diseased cells in the reticuloendothelial system.