To determine how interferon (IFN)-γ inhibits epithelial barrier and ion transport functions, intestinal T84 cells were studied.

Acute and chronic effects of IFN-γ on T84 barrier function, Na⁺,K⁺-adenosine triphosphatase (ATPase) activity, and certain ion transport and tight junctional proteins were determined. To assess the role of Na⁺,K⁺-ATPase and intracellular Na⁺, similar studies with the Na⁺,K⁺-ATPase inhibitor ouabain and Na⁺ ionophore monensin were performed. To determine the role of nitric oxide (NO), the NO donor SPER-NO was used.

IFN-γ acutely (<6 hour) decreased cellular Na⁺,K⁺-ATPase activity, followed later (>24 hours) by decreases in expression of Na/K/2Cl, the α subunit of Na⁺,K⁺-ATPase, occludin, and ZO-1. In contrast, cystic fibrosis transmembrane conductance regulator or the Na⁺ pump β subunit were unchanged. Ouabain and monensin caused nearly identical changes to IFN-γ. Incubation in low Na⁺ media significantly blunted the chronic effects of IFN-γ. Hypotonic-induced cell swelling, in contrast, had effects similar to IFN-γ but did not alter the expression of the Na⁺ pump α subunit. The NO donor SPER-NO rapidly inhibited Na⁺,K⁺-ATPase and also down-regulated transport and barrier proteins.

IFN-γ inhibition of Na⁺,K⁺-ATPase activity acutely causes increases in intracellular Na_i concentration and cell volume, which are distinct signaling events that ultimately result in a leaky and dysfunctional epithelium associated with chronic inflammation.