ERYTHROCYTE AUTOANTIBODIES, THE MONOCYTE MONOLAYER ASSAY AND INVIVO HEMOLYSIS

Monocyte monolayer assays (MMA) were performed using red cells (RBCs) from 159 patients with a positive direct antiglobulin test and monocyt es from healthy individuals. The results of the MMA reflected, to a gr eat extent, in vivo haemolysis; 56/63 patients with a positive result, but only 10/96 with a negative one, had evidence of in vivo RBC destr uction. Positive MMAs were observed with autoantibodies of all types: warm (42 cases), cold (14 cases), mixed (seven cases), but never in pa tients with only C3d on their RBCs and no detectable autoantibodies. W ith warm autoantibodies, the MMA results depended, in part, on the lev el of IgG sensitization: additional C3d coating acted synergistically to lower the amount of IgG necessary for monocyte interaction to occur . The presence of IgG3 as well as IgG1 on the RBCs was usually associa ted with a high MMA result; most of these cases, however, also exhibit ed larger amounts of cell-bound IgG. When the MMA results were analyse d in respect of the various types of autoantibodies, differences in th e phagocytosis: adherence ratio were observed: in patients with warm a utoantibodies, there was a preponderance of phagocytosis, whereas in t hose with cold and mixed types, adherent RBCs predominated or were fou nd alone.