Serum IgM, IgG and IgA block by F(ab′)2-dependent mechanism the binding of natural IgG autoantibodies from therapeutic immunoglobulin preparations to self-antigens

Natural polyreactive IgG autoantibodies are present in the plasma of healthy individuals and as a result in pooled therapeutic intravenous immunoglobulin (IVIg) preparations. The spectrum of self-antigens to which these autoantibodies bind, their fate after intravenous infusion and their biological activity are not well understood. The identity of serum proteins that mask binding of natural autoantibodies to self-proteins is a matter of controversy. The spectrum of native serum proteins bound by IVIg was analyzed by two-dimensional electrophoresis. The reactivity of IVIg was directed mainly to circulating immunoglobulins. The binding of the IgG autoantibodies from IVIg to native human liver antigens was blocked not only by a F(ab')(2)-dependent mechanism by circulating IgM and IgG (as has been previously suggested), but also by serum IgA. This control of anti-self reactivity may be inefficient in some autoimmune diseases.