Anti-inflammatory properties of probiotic bacteria on Salmonella-induced IL-8 synthesis in enterocyte-like Caco-2 cells

Invasion of the gut by pathogenic Salmonella leads to production of IL-8 that initiates inflammatory reactions to combat the bacterium. However, its persistent production causes tissue damage and interventions that suppress IL-8 production prevent tissue damage. We hypothesised that probiotics could mediate their benefits via inhibition of IL-8 synthesis. Caco-2 cells were infected with probiotic Bifidobacterium infantis W52, Lactobacillus casei W56, Lactococcus lactis W58, Lactobacillus acidophilus W70, Bifidobacterium bifidum W23, or Lactobacillus salivarius W24 or pathogenic Salmonella enterica serovar Enteritidis 857 at 0, 0.2, 1, 2, 10, 20, 100 or 200 bacterial cells/Caco-2 cell for 1 hour. Cells were also exposed to a combination of one probiotic bacterium (200 bacterial cells/Caco-2 cell) and the graded numbers of Salmonella as either co-incubation (1 hour) or pre-incubation of the probiotic bacterium (1 hour) followed by Salmonella (1 hour). The cells recovered for 2 or 24 hours. IL-8 and Hsp70 were determined by ELISA and Western blot respectively. Both probiotics and Salmonella induced a dose-and time-dependent synthesis of IL-8 but probiotics induced far lower IL-8 levels than Salmonella. The Salmonella-induced IL-8 was significantly suppressed by B. infantis W52, L. casei W56 and L. lactis W58 at low numbers of Salmonella (0.2 to 20 bacterial cells/Caco-2 cell) and within 2 hours of recovery. The observed probiotic-mediated reduction in IL-8 secretion was transient, and lost after a few hours. In addition, these three probiotics induced a significant increase in Hsp70 expression while L. acidophilus W70, B. bifidum W23 and L. salivarius W24 induced a weak Hsp70 expression and could not suppress the Salmonella-induced IL-8 synthesis. We conclude that suppression of Salmonella-induced IL-8 synthesis by Caco-2 cells is exhibited by probiotics that induce expression of Hsp70, suggesting that the protective role of probiotics could be mediated, at least in part, via Hsp70 expression. This suppression is limited to a low number of infecting pathogenic Salmonella.