Effect of Type I Interferon(s) on Cell Viability and Apoptosis in Primary Human Thyrocyte Cultures

Background: Interferon (IFN) therapy may induce a generalized activation of the immune system, hence triggering or exacerbating autoimmune disease. Apoptosis contributes to the development of hypothyroidism in autoimmune thyroiditis. IFN can affect all phases of the cell cycle and may induce apoptosis in several cell lines from varied histologies. To date, no data exist on the possible effect of type I IFN(s) on FAS/FASL system and cell apoptosis of human thyroid follicles. Therefore, we evaluated the effect of both IFN-alpha and -beta on apoptosis in primary human thyrocyte cultures and the potential role of the FAS/FASL pathway. Methods: Thyrocytes were cultured in monolayers and FAS, FASL, and Bcl-2 mRNA expression was determined by reverse transcriptase polymerase chain reaction after exposure to 10mIU/mL bovine thyroid-stimulating hormone alone or in combination with increasing doses of IFN-alpha or -beta for 24, 48, and 72 hours. The percentage of apoptotic hypodiploid cells was evaluated by flow cytometry. Results: Thyroid-stimulating hormone significantly decreased FAS and increased Bcl-2 mRNA expression while reducing the percentage of hypodiploid cells. The concomitant addition of either IFN-alpha or- beta reduced cell viability and increased the number of hypodiloid cells, but only IFN-beta modulated the expression of FAS and Bcl-2 mRNA expression in a proapoptotic sense. Conclusions: Both type I IFN(s) increase apoptosis in primary thyrocyte cultures, but only IFN-beta modulates FAS and Bcl-2 gene expression toward a proapoptotic pathway. Because apoptosis plays an important role in thyroid homeostasis and disease, this mechanism may contribute to the development and progression of type I IFN(s) therapy-associated thyroid disease.