Interferon-gamma down-regulates claudin-1 and impairs the epithelial barrier function in primary cultured human thyrocytes.

OBJECTIVE

Proinflammatory cytokines are known to affect the follicular epithelium in autoimmune thyroid disease. Here we investigated the effect of interferon-gamma (IFN-gamma) on the barrier function of primary cultured human thyrocytes.

DESIGN

Graves' thyroid follicle segments were cultured as a tight and polarised monolayer on the filter of a bicameral chamber, thereby allowing the in vivo epithelial characteristics to be maintained.

METHODS

Transepithelial electrical resistance was measured with a Millicell ERS ohmmeter. The tight junction proteins claudin-1 and occludin were analysed by immunofluorescence and Western blotting. Cell morphology was studied by transmission electron microscopy.

RESULTS

Thyrotrophin (TSH; 1 mU/ml) promoted the development of a tight epithelium monitored as a persistent increase in the transepithelial resistance to about 800 omega x cm2. IFN-gamma (100 U/ml), on the other hand, decreased the resistance to 60-150 omega x cm2 after 48 h. In IFN-gamma-treated cells the expression of claudin-1, but not that of occludin, was decreased along with a diminished intracellular and cell surface immunostaining. In addition, claudin-1 was disrupted at cell-cell contacts. IFN-gamma also caused profound cell shape changes and a multilayered cellular organisation, without ultrastructural or biochemical (caspase-3 activity) signs of cytotoxicity. TSH was unable to counteract the effects of IFN-gamma.

CONCLUSIONS

IFN-gamma destroys the barrier function of filter-cultured human thyroid epithelial cells. The loss of barrier involves down-regulation and an altered distribution of claudin-1. This novel effect of IFN-gamma on target cells in thyroid autoimmunity might be of pathophysiological relevance to the exposure of hidden autoantigens.