Do IgE-IgG complexes occur in the circulation?

IgG anti-IgE autoantibodies in human allergic sera have been investigated using an enzyme immunoassay on microplates coated with anti-human IgE MoAb. After incubation with serum, the plates were developed with peroxidase-labelled anti-human IgE MoAb for the determination of total IgE levels, or with anti-IgG MoAb for evaluating IgG anti-IgE autoantibodies. Using this methodology, no correlation was found between total IgE and IgG anti-IgE levels in groups of sera of allergic individuals. Although the results obtained with enzyme-labelled anti-IgG are often interpreted as indicative of IgE-IgG complexes captured from the serum, molecular sieving on gel columns as well as direct ultrafiltration experiments through 300-kD membranes demonstrate that such complexes do not occur preformed in the circulation, but arise de novo on the anti-IgE-coated solid phase during in vitro incubation with human serum. It is suggested that IgG anti-IgE autoantibodies react with IgE only after the latter has undergone a conformational change, either by colloidal manipulation or after reaction with allergen.