Synergistic effect of blending IgG1 and IgG3 monoclonal anti-D in promoting the metabolic response of monocytes to sensitized red cells.

Monoclonal antibodies specific for the Rh antigen D were used to sensitize red cells for use in a series of cellular assays. IgG3 anti-D was more efficient than IgG1 anti-D in promoting the attachment and lysis of red cells by human monocytes. In contrast, IgG1 anti-D was more efficient at mediating phagocytosis. The metabolic response of monocytes, measured by chemiluminescence (CL), was greater towards IgG3-sensitized red cells than IgG1-sensitized cells; however, the CL response was further increased when red cells were sensitized in antibody mixtures comprising both subclasses. Using monoclonal antibodies from five IgG1-secreting cell lines and from three IgG3-secreting cell lines, this synergistic increase was seen with 0/4 IgG1/IgG1 combinations, 0/2 IgG3/IgG3 combinations and 8/8 IgG1/IgG3 combinations. Synergism was observed only when both subclasses were present on the same red cells; mixing of IgG1-sensitized red cells with IgG3-sensitized red cells before addition to monocytes did not increase CL generation. The binding and phagocytosis of red cells by monocytes and the lysis of red cells by monocytes or lymphocytes were not greater when red cells were sensitized with IgG1 and IgG3 antibodies together compared to red cells coated with single subclasses.