Mode of inactivation of probiotic bacteria affects interleukin 6 and interleukin 8 production in human intestinal epithelial-like Caco-2 cells

Five lactic acid bacteria and two bifidobacteria strains were heat or irradiation inactivated. Inactivated cultures were evaluated for their effects on cytokines interleukin (IL) 6 and IL-8 production in human intestinal-like Caco-2 cells. For both heat- and irradiation-inactivated cultures, production of IL-6 and IL-8 was dependent on the specific microorganism. However, with all of the cultures, both IL-6 and IL-8 production was significantly higher (P < 0.05) in Caco-2 cells that were treated with heat-inactivated probiotic bacteria compare to the irradiation-inactivated bacteria. In the majority of the cases, heat-inactivated bacteria induced IL-6 and IL-8 production, whereas irradiation-inactivated bacteria attenuated both cytokine production. Our results indicate that the same probiotic bacteria used in the same cell culture could provide opposite cytokine production and immune modulation results based on its mode of inactivation; therefore, it is important to describe inactivation methods and conditions in detail when characterizing probiotic effects.