Activation, proliferation, and differentiation of circulating B cells in autoimmune thyroid disease

Several studies of thyroid autoantibody production in vitro have been reported with the use of pokeweed mitogen, but the conclusions that have resulted regarding the immunoregulation of B cell function in thyroid disease are difficult to interpret due to the relatively nonphysiologic nature of pokeweed mitogen stimulation. We have therefore examined the responses of circulating B cells in Graves' disease and Hashimoto's thyroiditis by using a combination of lymphokines and other stimuli that act at various stages of the B cell cycle. In patients with autoimmune thyroid disease, nonspecific B cell proliferation and differentiation into IgG-secreting cells were both normal. However, a previously unsuspected heterogeneity among patients was found in their ability to produce autoantibodies in vitro. B cells of certain patients produced maximal autoantibody in response to pokeweed mitogen, some in response to Staphylococcus aureus Cowan strain I, and some in response to the lymphokines contained in the supernatants of stimulated T cell cultures. There was no correlation between serum autoantibody levels and those achieved in vitro. Attempts to stimulate antibody production by autoantigen (thyroglobulin) were unsuccessful, even when B cells were cultured with purified autologous OKT4+ T cells to avoid potential suppressor effects in the OKT8+ population. However, OKT4+ T cells enhanced pokeweed mitogen-driven autoantibody production. Our results show that several different functional stages of B cells exist in the circulation of patients with autoimmune thyroid disease, and that circulating B cells from such patients do not manifest a uniform response to B cell stimulators. This is presumably the result of differences in migration of circulating B cells and in their level of activation at the major sites of autoantibody production, such as the thyroid gland itself. In the light of these findings, caution is required in interpreting the results obtained from studies of circulating B cells as a means of elucidating the pathophysiology of autoimmune thyroid disease.