Reversible inhibition by interferons alpha and beta of 125I incorporation and thyroid hormone release by human thyroid follicles in vitro.

When interferons (IFN-alpha-2a, IFN-alpha-2b, natural IFN-alpha and IFN-beta) were cultured with human thyroid follicles, each IFN inhibited TSH-induced thyroid function (125I incorporation and release of 125I-T4) in a concentration-dependent manner. The minimal inhibitory effect was exerted at 1-10 U/ml. However, the inhibitory effect was reversible, and no inhibitory effect was detected when IFNs were removed from the medium within 12 h. These in vitro findings suggest that each IFN directly inhibits human thyroid function at clinically attainable levels. However, since the inhibitory effect was reversible, IFN therapy would provoke only subtle thyroid dysfunction in a majority of patients without preexisting thyroid autoimmunity.