TUMOR-NECROSIS-FACTOR-ALPHA MODULATES THE EXPRESSION OF ITS P60 RECEPTOR AND SEVERAL CYTOKINES IN RAT TRACHEAL EPITHELIAL-CELLS

The epithelium of the conducting airways is frequently the target of t oxic chemical and microbial agents causing inflammation, hypersecretio n, and epithelial necrosis. TNF-alpha is a prototypical inflammatory c ytokine released by macrophages and other inflammatory cells. The purp ose of this study was to characterize TNF-alpha receptors in fully dif ferentiated rat tracheal epithelial (RTE) cells in culture and to exam ine the effects of TNF-alpha on this epithelium. We demonstrated the p resence of approximately 250 TNF-alpha receptors per RTE cell. Both kn own receptor types, p60 (TNF-RI, CD 120a) and p80 (TNF-RII, CD 120b), were expressed. The level of p80 mRNA was unaffected by TNF-alpha trea tment, whereas p60 mRNA was down-regulated, and soluble TNF-RI was she d from cells within 30 min. Treatment of RTE cultures with TNF-alpha ( 1000 U) caused no cytotoxicity (as determined by lactate dehydrogenase release). However, TNF-alpha exposure of the cultures induced the exp ression of several inflammatory mediators, as determined by reverse tr anscription-PCR and ELISA. Low levels of IFN-gamma mRNA became detecta ble after 4 h. Increased levels of TNF-alpha mRNA and protein were fou nd, which peaked after 6 h of TNF-alpha treatment, but neither IL-1 al pha nor IL-1 beta was detectable. Calcium-independent nitric oxide;syn thase transcripts were elevated two- to threefold within 2 to 6 h of T NF-alpha treatment. These findings suggest that the airway epithelium may actively participate in the pathogenesis of airway inflammation th rough the production of mediators similar to those found in a Th1 resp onse.