Fig. 3.
IgM inhibits the reactivity of purified autologous IgG with autologous blood group antigens. IgG was purified from serum of individuals of blood groups A1 (□), B (◊), O (▵), and AB (○) and incubated with the respective autologous IgG-depleted fractions of serum used as sources of IgM at a ratio of IgG to IgM (wt/wt) of 1:10 for 1 hour at 37°C. The reactivity of IgG with A (left panel) and B antigens (right panel) was then assessed by ELISA. Each data point represents the mean OD ± SD of binding of IgG from four individuals of each blood group category. The binding of IgG of individuals of blood group A to A antigen in the presence of autologous IgM was significantly lower than the binding of IgG of individuals of blood group B coincubated with autologous IgM (P < .0001). Similarly, the binding of B IgG to B antigen in the presence of B IgM was significantly lower than that of A IgG in the presence of A IgM (P < .0001).