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.