Lactobacillus pentosus (L. pentosus) strain S-PT84, isolated from Kyoto pickles, enhances splenic natural killer (NK) cell activity, and has high T-helper1 (Th1) cytokine and type 1-IFN (IFN-α) inducing activity. In the present study, we investigated the influence of S-PT84 ingestion on the mucosal immunity of healthy and Salmonella Typhimurium (S. Typhimurium)-infected mice. In the S. Typhimurium infection model, numbers of S. Typhimurium in feces and the spleen were significantly decreased, and body weight loss and deterioration in the general health score of S. Typhimurium-infected mice were improved by S-PT84 ingestion. Oral administration of S-PT84 enhanced IL-5 and IL-6 production from Peyer's patch cells in vitro, with a concomitant significant increase in IgA production from Peyer's patch cells, which may explain the mechanism of enhanced IgA production in the small intestine in vivo. These results suggest that S-PT84 ingestion is useful for the maintenance of health or the improvement of certain symptoms during pathogen infection.

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In vitro M cell models, consisting of co-cultures of Caco-2 cells and lymphoid cells, were developed and examined to observe bacterial transport. However, under our experimental conditions, the differentiation of Caco-2 cells into M cell-like cells could not be induced efficiently. To obtain a functionally stable M cell model based on human cells, C2BBe1 cells were screened and co-cultured with human Raji cells. In our co-cultures, increased sialyl Lewis A antigen expression and decreased Ulex europeaus agglutinin 1 binding were observed. Regarding the functional properties of the model, microsphere and lactic acid bacteria transport across the C2BBe1 co-cultures were increased compared with the levels seen in monocultures. The C2BBe1 monolayers that were co-cultured with Raji cells exhibited some M cell features; therefore, we consider our M cell model to be useful for investigating the interactions of bacteria with M cells.

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