Intestinal intraepithelial T cells (IELs) expressing either gammadelta TCR or alphabeta TCR have been proposed to play an important role in the regulation of intestinal epithelia by producing cytokines that directly influence the adjoining intestinal epithelial cell (IEC) functions. To illuminate this issue, we utilized TCR mutant mice to obtain gammadelta IELs, alphabeta IELs and mixed gammadelta and alphabeta IELs from corresponding alphabeta T-cell-deficient (beta-/-), gammadelta T-cell-deficient (delta-/-) and wild-type (WT) littermate mice. The production of IFN-gamma by these IELs as well as the mRNA for IFN-gamma, TGF-alpha, TGF-beta1, TNF-alpha and TNF-beta in these IELs, in conjunction with the effect of produced cytokines on the expression of class II MHC molecules by the in vitro cell line IEC-6, were investigated. IFN-gamma and TNF-alpha [corrected] specific mRNA were detectable in all freshly isolated gammadelta, alphabeta and WT IELs. In addition to the IFN-gamma and TNF-alpha [corrected] mRNA, alphabeta and WT IELs that had been activated in culture plates coated with anti-CD3 mAb contained mRNA for TGF-beta1 and TNF-beta proteins. In the cultured gammadelta IELs, however, the signals for IFN-gamma and TNF-alpha [corrected] transcripts were weak, and mRNA for the latter two cytokines was almost undetectable. Supernatants from in vitro culturing of alphabeta and WT IELs but not gammadelta IELs induced class II MHC gene expression in IEC-6, whereas, in the presence of anti-IFN-gamma mAb, the same culture supernatants failed to do so. In fact, the concentration of IFN-gamma in supernatants from alphabeta and WT IEL cultures was ten- to twentyfold higher than that in the supernatant from the gammadelta IEL culture. Finally, TGF-alpha specific mRNA was not detectable in the gammadelta and alphabeta IELs even after in vitro activation. These results indicate that alphabeta IELs are superior to gammadelta IELs in the ability to produce IFN-gamma, TGF-beta1, TNF-alpha [corrected] and TNF-beta through TCR crosslinking primary in vitro stimulation.