TNF-α pretreatment of Salmonella contributes to enhanced bacterial invasion in human intestinal epithelial HCT116 cells. (A) and (B) Number of internalized Salmonella (A: SL1344; B: SL1344 AvrA-) in the HCT116 cells. (C) and (D) Number of Salmonella associated with HCT116 cells. C: SL1344; D: SL1344 AvrA-. (E) Number of internalized Salmonella in the HCT116 cells with a JNK inhibitor SP600125 (50 μM) pretreatment. HCT116 cells were stimulated with Salmonella with or without TNF-α pretreatment for 30 min, washed, and incubated in fresh DMEM for 30 min. For both cell associated and internalized bacteria, 0.9 ml LB broth was then added and each sample was vigorously mixed and quantitated by plating for CFU on MacConkey agar medium. The mean ± SD is from three replicate experiments.