Host IL-8 and TNF expression in response to F18 E. coli infection. A-B, transcription of il8 and tnfa in Caco-2 cells after a 2 h infection with the indicated bacterial strains. Data were normalized to the housekeeping gene gapdh; C-D, ELISA, secretion of IL-8 and TNF into Caco-2 cell supernatants after a 2 h infection with the indicated bacterial strains was quantified using ELISAs.