Separate Induction of MHC and Thyroid Microsomal Antigen (McAg) Expression on Thyroid Cell Monolayers: Enhancement of Lectin-Induced McAg Expression by Interferon-γ*

Interferon-gamma (IFN gamma) induced the expression of the MHC class II antigens HLA-DR and -DQ on 1- to 2-week-old thyrocytes from normal thyroid tissue and thyroid tissue from patients with autoimmune thyroid disease; it also enhanced the expression of B2-microglobulin, which is associated with MHC class I molecules. However, the expression of thyroglobulin and thyroid microsomal antigen (McAg) was not detected after IFN gamma stimulation. Autologous and allogeneic peripheral blood mononuclear cells had the same ability as IFN gamma to induce antigen expression when cocultured with thyrocytes. In contrast, leucoagglutinin (LAG) induced McAg as well as HLA-DR and B2-microglobulin expression on thyrocytes, but not thyroglobulin expression. Concanavalin A and pokeweed mitogen also induced McAg expression. The time course of LAG induction of McAg was not always correlated with that of HLA-DR. Anti-IFN gamma, antiinterleukin-2 receptor, and anti-HLA-DR monoclonal antibodies inhibited LAG or peripheral blood mononuclear cell induction of HLA-DR expression, but not LAG induction of McAg expression. Anti-HLA-DR reduced the IFN gamma induction of HLA-DR. INF gamma enhanced thyrocyte McAg expression induced by LAG, especially when thyrocytes were incubated with IFN gamma for 24 h before LAG stimulation. In contrast, in the absence of LAG stimulation, IFN gamma suppressed already present spontaneous McAg expression. TSH did not induce McAg and HLA-DR expression on DR-negative thyrocytes, but enhanced weak DR expression induced by other stimulants, e.g. IFN gamma or lectins. These data suggest that in vitro induction mechanisms of MHC class I and II antigens and McAg are different; MHC antigens are induced by IFN gamma, whereas McAg is induced by lectin, probably acting on thyrocytes directly; and IFN gamma has an enhancing effect on LAG-induced thyrocyte McAg expression.