Heat- and formalin-inactivated probiotic bacteria induce comparable cytokine patterns in intestinal epithelial cell-leucocyte cocultures

The mode of inactivation of probiotic bacteria may profoundly affect their immune-modulatory properties to the point of reversal of effects in in vitro human intestinal epithelial-like cell cultures (Caco-2). To further investigate the influence of inactivation treatment on cytokine production, three probiotic strains were evaluated-live, heat-inactivated, and formalin-inactivated strains-for their impact on interleukin (IL) 6, IL-8, and IL-10 production in Caco-2-leucocyte cocultures. The tested bacteria induced strain-specific production of IL-6, IL-8, and IL-10. No suppressive effects on cytokine synthesis were observed. Live microorganisms seemed to be slightly more potent inducers of cytokine production than nonviable strains, but differences to inactivated bacteria were not statistically significant. Our results indicate that heat and formalin treatments of probiotic microorganisms are equivalent inactivation methods in terms of induction of IL-6, IL-8, and IL-10 production in Caco-2-peripheral blood mononuclear cell cocultures and do not invert immune-modulatory effects.