Inhibition of Salmonella-induced IL-8 synthesis and expression of Hsp70 in enterocyte-like Caco-2 cells after exposure to non-starter lactobacilli

Oral administration of lactobacilli as probiotics is gaining importance in the treatment of intestinal inflammations. We investigated the effect of non-starter lactobacilli Lactobacillus casei subsp casei 2756, Lactobacillus curvatus 2775, and Lactobacillus plantarum 2142 as well as their spent culture supernatants (SCS) on Salmonella enteritidis 857 growth, interleukin (IL)-8 and heat shock protein 70 (Hsp70) synthesis in undifferentiated crypt-like and differentiated villus-like Caco-2 cells. The cells were infected with graded numbers of non-starter lactobacilli or S. enteritidis 857 for 1 h and allowed to recover for 24 h or exposed to 200 bacteria/cell for 1 h and allowed to recover for different periods of time. In another experiment S. enteritidis 857 was first pre-treated with SCS-lactobacilli for 1 h before infecting the cells. The levels of IL-8 and Hsp70 were assessed using sandwich ELISA and immunostaining of Western blots, respectively. The effect of SCS-lactobacilli on S. enteritidis 857 growth was evaluated by agar plate diffusion test. The non-starter lactobacilli induced a significant increase in the levels of both IL-8 and Hsp70. However, compared with the S. enteritidis 857 induced IL-8 synthesis, the levels of IL-8 induced by the lactobacilli at any equivalent bacterial number were far lower. After exposure of Caco-2 cells to S. enteritidis 857 pre-treated with SCS-lactobacilli, it appeared that their SCS inhibited the S. enteritidis 857 growth and IL-8 synthesis and in addition induced the expression of Hsp70. The differences in response of crypt- and villus-like Caco-2 cells are merely a reflection of their differentiation status. Our data suggest that the beneficial effect of non-starter lactobacilli to the intestinal inflammations might be associated with a decrease of the IL-8 levels. This effect could be mediated, at least in part, by the bacteria themselves or via a secreted antimicrobial product(s) either directly against the pathogens or indirectly through the synthesis of Hsp70.