TNF and cystic fibrosis: Although we observed no significant differences in the ability of non-CF control or CF CD4 or CD8 T cells to produce IFN-γ/TNF in response to S. pyogenes, S. aureus, or CEF peptides, we noted a striking and significant reduction in the frequency of both CD4 (Fig. 3E) and CD8 (Fig. 3F) CF T cells producing IFN-γ/TNF following stimulation with PMA/I compared to non-CF controls.