Postpartum activation of autoimmunity: transient increase of total IgG levels in normal women and in women with autoimmune thyroiditis.

The immunoregulatory mechanisms underlying the transient rebound of autoimmune disease activity in the postpartum period were studied by determining serum immunoglobulins, thyroid microsomal antibodies and some viral (cytomegalovirus, Epstein-Barr, varicellae-zoster and mumps) and bacterial (Yersinia enterocolitica and Salmonella) antibodies in women with autoimmune thyroiditis and in healthy postpartum women. A characteristic increase between 2 and 5 months postpartum followed by a decrease to 10-12 months postpartum was observed not only for thyroid microsomal antibody titres in women with autoimmune thyroiditis but also for serum total IgG and IgG subclass levels (but not IgM, IgA or IgE) in both groups of women. This pattern of transient antibody increase was not detected against viral and bacterial antigens. The characteristic alterations of thyroid microsomal antibody titres in the postpartum period of women with autoimmune thyroiditis thus appear to occur as a consequence of an activation of immunoglobulin-producing B cell clones. This activation seems restricted to the IgG class and to certain B cell clones.