Immunostimulatory actions of lactobacilli:: Mitogenic induction of antibody production and spleen cell proliferation by Lactobacillus delbrueckii subsp bulgaricus and Lactobacillus acidophilus

We investigated the ability of heat- treated Lactobacillus delbrueckii subsp. bulgaricus and Lactobacillus acidophilus to act as direct inducers of antibody production and cellular proliferation. Yogurt starter- derived strains of L. delbrueckii subsp. bulgaricus and L. acidophilus induced high levels of antibody production by murine splenocytes in vitro. Both IgM and IgG isotypes were produced. In contrast, two different strains, L. delbrueckii subsp. bulgaricus (ATCC 11977) and L. acidophilus (ATCC 521) did not induce antibody production by murine splenocytes. While all four strains were able to induce some degree of splenocyte proliferation, the yogurt starter- derived strain of L. acidophilus was the most potent inducer. These results indicate a mitogenic effect of certain strains of lactobacilli on murine splenocytes, resulting in polyclonal antibody production. The ability of heat- treated lactic acid bacteria to induce antibody production and proliferation suggests the involvement of a heat- resistant structural component in non- specific activation of the immune system by these strains of lactic acid bacteria.