The relationship between antibody concentration and target cell number in the induction of K cell-mediated haemolysis: Evidence for asymmetry among reactants

The cytotoxic capacity of peripheral blood mononuclear cells for anti-D sensitized human O Rh(D) + ve (R1R2) erythrocytes was measured under conditions where antibody concentrations and target cell number were varied with respect to each other. It was observed that where sensitization was limiting, due either to target cell excess or increased antibody dilution, the relationship between lysis and antibody concentration was non-linear, and that the end-point dilution of anti-D at which measurable cytotoxicity occurred was dependent upon the source or concentration of effector cells. The asymmetrical relationship between cytotoxic activity and the degree of sensitization suggests that, in this system at least, there is extensive heterogeneity either among target erythrocytes in terms of their degree of sensitization and consequent susceptibility to lysis, and/or among effector cells in terms of their sensitization requirements for induction of cytotoxicity.