Aglycosylated chimaeric human IgG3 can trigger the human phagocyte respiratory burst

This study investigates the capacity of a complexed aglycosylated chimaeric human IgG3 antibody to induce the respiratory burst in human monocyte-like U937 cells. It demonstrates that the aglycosylated antibody, prepared by cell culture in tunicamycin, retains significant capacity to trigger this effector function which was assayed as superoxide generation. Erythrocytes sensitized with near maximal levels of aglycosylated IgG3 were able to trigger > 80% of the superoxide generation triggered by the glycosylated antibody from U937 cells induced to differentiate by interferon gamma and the aglycosylated IgG3 gave half maximal responses at sensitization levels only 72% higher than those required by the glycosylated form. Aglycosylated IgG3 was, however, much less effective in triggering superoxide generation by interferon gamma treated U937 cells at low sensitization levels as threshold responses required only 60 glycosylated IgG3 molecules per erythrocyte compared with 16,000 aglycosylated molecules. In addition, these studies indicate significant differences between the target cell to effector cell ratios which permit IgG sensitized erythrocytes to stimulate the respiratory burst and those which stimulate ADCC in the same effector cell type.