Induction of thyroid autoantibody production: synergistic effect of B cell mitogen combined with T cell mitogen

In vitro production of thyroglobulin autoantibodies (TgAb) and thyroid microsomal autoantibodies (McAb) by peripheral blood mononuclear cells (PBMC) stimulated with the B cell mitogen Staphylococcus aureus Cowan I (SAC) and the T cell mitogen pokeweed mitogen (PWM) was examined in 35 normal subjects (NC) and 64 patients with autoimmune thyroid disease (AITD) using an enzyme-linked immunosorbent assay technique. Low concentrations of SAC plus PWM resulted in a synergistic effect on thyroid autoantibody production as well as nonspecific immunoglobulin G production. With such maximal stimulation, TgAb production was detected in all PBMC preparations from serum TgAb-positive patients with AITD; TgAb production was also detected in some NC (46%) and serum TgAb-negative patients with AITD (39%), but the levels of TgAb production were low. Similarly, McAb production was marked in PBMC preparations from serum TgAb-negative but McAb-positive patients. TgAb-secreting cells were also detected in NC by the plaque-forming cell (PFC) assay. The response patterns of PBMC to mitogen (Nil, PWM, and SAC plus PWM) in terms of TgAb production varied among serum TgAb-positive patients with AITD, but not among NC and serum TgAb-negative patients with AITD. Serum TgAb titers were significantly correlated with the in vitro production of TgAb by PBMC with no stimulation (r = 0.64; n = 99; P less than 0.001), with stimulation by PWM (r = 0.75), and with stimulation by SAC plus PWM (r = 0.87); the correlation coefficient increased with the efficiency of stimulation of B cell differentiation. Similar results were found for McAb production. These data suggest that 1) optimal in vitro thyroid autoantibody production occurs with B cell mitogen (SAC) acting synergistically with T cell mitogen (PWM); 2) sufficient numbers of resting B lymphocytes specific for Tg or microsomal antigens are present in some NC PBMC; 3) stages of thyroid-specific B cell differentiation in PBMC vary among serum thyroid autoantibody-positive patients with AITD; and 4) the potential of PBMC to produce thyroid autoantibodies may correlate with the capacity of thyroid-derived lymphocytes. Thus, the circulating lymphocytes may provide a useful vehicle by which sequential changes occurring at the tissue level may be examined.