In the present study we have analyzed the changes in the expressed antibody repertoire and in temporal fluctuations of antibody levels in serum that followed infusion of normal IgG (IVIg) in a patient with autoimmune thyroiditis. Administration of IVIg resulted in the stimulation of IgM production, in alterations of expressed antibody activity in serum that could not merely be accounted for by the passive transfer of antibody specificities contained in IVIg, in transient down-regulation of B cells clones expressing a specific disease-related idiotype and in the increase in serum in recipient’s autoantibodies specifically reactive with F(ab′)2 fragments of IVIg. In addition, infusion of IVIg shifted the pattern of spontaneous fluctuations of autoantibody activities in the patient’s serum from a pattern indicative of disconnected events in the immune network to a pattern similar to that which is consistently observed in healthy controls. These results suggest that normal IgG may modulate autoreactivity by selecting expressed antibody repertoire through V region-dependent interactions with antibodies.

Key words: autoimmunity, IgG, intravenous immunoglobulin (IVIg), immune networks

We have measured the quantities of naturally occurring autoantibodies in the serum of normal, unmanipulated individuals. These changes over time following broad-band complex dynamical patterns that are similar in mouse and man. The patterns more likely reflect the network architecture of the natural antibody repertoire, regulating the activation and decay of individual clones. The temporal changes of both disease-specific and nonspecific autoantibodies are consistently modified in autoimmune individuals.