Red-cell bound anti-A is more efficient than anti-B in competition for fluid phase complement.
Lysis of group A and B erythrocytes by human complement was studied by an anti-A (BRIC.131) and an anti-B (BRIC.30) IgM monoclonal antibody in a 51Cr-release assay. The relative concentration of membrane-bound immunoglobulins was detected by flow cytometric analysis, and the amount of C1q and C3 bound to the sensitized red cells was measured by using purified, 125I-labelled molecules. The direct haemolysis was identical with both reagents in the presence of excess and suboptimal complement over a wide range of antibody concentration (between 50 and 7000 ng/ml). The indirect effect of membrane-bound antibody, i.e. its influence on complement binding by sensitized bystander cells, was examined in a cold target competition assay in which sensitized, non-labelled cells are present when complement is incubated with sensitized labelled cells. We have found that the competitive capacity of sensitized erythrocytes correlated with the amount of membrane-bound immunoglobulins. In accordance with our earlier findings, an equal level of target and competitor cell lysis was obtained only if the fluid phase anti-B antibody concentration was 2 to 4 times higher than that of the anti-A antibodies. We demonstrate in this paper that the different competitive activity of IgM anti-A and anti-B monoclonal antibodies might be accounted for by differences in their C1q and C3 binding capacities.
Bakács
T
T
Department of Immunology, National Institute of Oncology, Budapest, Hungary.
Tusnády
G
G
Végh
Z
Z
Merry
A H
AH
Kertész
Z
Z
Klein
E
E
D000017:ABO Blood-Group System / Q000276:immunology*; D000911:Antibodies, Monoclonal / Q000276:immunology; D001667:Binding, Competitive / Q000276:immunology; D003167:Complement Activation / Q000276:immunology; D015922:Complement C1q / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology*; D015941:Complement Hemolytic Activity Assay; D004910:Erythrocyte Membrane / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology
D000017:ABO Blood-Group System; D000911:Antibodies, Monoclonal; D003176:Complement C3; D007075:Immunoglobulin M; D015922:Complement C1q