T cell-monocyte interactions regulate epithelial physiology in a coculture model of inflammation

We have examined the effect of T cell activation, with or without monocytes, on epithelial electrolyte transport and barrier functions. Confluent monolayers of human T84 epithelial cells were cocultured (1-3 days) with peripheral blood mononuclear cells (PBM) or T cells activated by anti-CD3 antibody. Monolayers were then mounted in Ussing chambers, and changes in ion transport (indicated by short-circuit current, I-sc) and barrier (indicated by resistance and radiolabeled probe fluxes) functions were assessed. Coculture with activated PBM or conditioned medium from these cells altered the transport (decreased I-sc responses to carbachol and forskolin) and barrier (decreased resistance and increased fluxes of [H-3]mannitol and Cr-51-EDTA) properties of T84 monolayers. In contrast, coculture with equal numbers of T cells activated in the absence of monocytes did not significantly affect epithelial physiology. Monocytes treated with conditioned media from activated T cells evoked epithelial abnormalities similar to those caused by culture with activated PBM. Total correction of epithelial abnormalities was achieved only by treating T cell-conditioned medium with anti-interferon-gamma (IFN-gamma) before addition to monocytes, as well as addition of anti-tumor necrosis factor-alpha (TNF-alpha) to the coculture. Exogenous recombinant IFN-gamma and TNF-alpha added to T84 monolayers did not mimic the physiological changes induced by immune cells; addition of these cytokines to monocytes did reproduce the effects. We conclude that T cell-derived IFN-gamma activates monocytes to release TNF-alpha and other soluble mediators, resulting in epithelial dysfunction.