Dissociation of IgG aggregates at low pH

Previous studies have reported that antigen-antibody complexes dissociate at low pH while IgG aggregates do not, and it has been suggested that dissociation of high molecular weight IgG in serum at low pH supports the presence of circulating antigen-antibody complexes. Our studies confirm the observation that heat-aggregated IgG does not dissociate at low pH. By contrast, non-thermal IgG aggregates, formed in isolated IgG preparations or in hypoalbuminemic serum and which may also form in vivo, are almost totally dissociated at low pH. Consequently dissociation of high molecular weight IgG in serum at low pH does not distinguish antigen-antibody complexes from IgG aggregates.