Evidence for presence of Ig64 anti-immunoglobulin autoantibodies in all human beings

IgG4 anti-IgG autoantibodies were found to be present in all serum samples from a group of healthy people; IgG4 anti-IgA and anti-IgE were present in only 13 of 218 (6%) and 8 of 218 (3.5%) samples, respectively. These antibodies also showed affinities towards animal immunoglobulins. We suggest that IgG4 anti-IgA antibodies (the strongest found heterophilic immunoglobulins) are responsible for most artifacts obtained with commercial ELISA systems.