Lactobacillus GG and L. gasseri TMC0356 were examined for their potential to alter the immune responses of murine PP cells in vitro and in vivo. Lactobacillus GG and L. gasseri TMC0356 characteristically stimulated the production of IL-12, IL-6, IFN-γ and IgA from isolated PP cells in vitro. Anatomical analysis indicated uptake of these bacteria by the PP tissue after giving orally in mice. Isolated PP cells exposed to Lactobacillus GG in vivo secreted more IFN-γ, IL-6 and total IgA, whereas those exposed to L. gasseri TMC0356 in vivo did not exhibit altered immune responses in terms of cytokine and IgA production. Therefore, these two bacteria might exhibit different immunodulatory effects in host animals by strain-dependent interaction with gut-associated lymphoid tissues in vivo.