Immunomodulating and anti-infective effects of a novel strain of Lactobacillus paracasei that strongly induces interleukin-12

Several studies have demonstrated that some strains of lactic acid bacteria (LAB) can elicit natural killer (NK) cell activities via interleukin-12 (IL-12) induction and protect against influenza virus (IFV) infection. LAB strains that strongly induce IL-12 are expected to be effective in protecting against IFV infection. In this study, we screened 85 strains for their ability to induce the in vitro production of IL-12, and Lactobacillus paracasei MoLac-1 most strongly induced IL-12. To examine the immunomodulating effects of MoLac-1, we have performed in vitro studies using murine splenocytes. Heat-killed MoLac-1 cells induced IL-12 and interferon-? (IFN-?) production by murine splenocytes. Experiments using splenocytes depleted of various cell populations indicated that macrophages might be a major source of MoLac-1-induced IL-12 secretion. Intracellular staining of IFN-? suggested that MoLac-1 activated NK cells and induced IFN-? production by NK cells in vitro. Oral administration of heat-killed MoLac-1 increased the proportion of NK cells in spleen, and ameliorated the symptoms of IFV infection in mice. These results suggest that heat-killed MoLac-1 has the potential to modulate innate immunity and is useful for alleviation of the symptoms of IFV infection.