Some lactic acid bacteria (LAB) function as probiotics. The beneficial functions brought by LAB on gastrointestinal conditions, such as constipation, diarrhea, inflammatory bowel disease, Helicobacter pylori infection, lactose intolerance, and colon cancer, have been reported. 1,2) LAB have also been found to modulate systemic and/or intestinal immune responses, including allergies, [3][4][5][6][7][8][9][10] although their application in medical treatment is still far from possible. It is important to accumulate information about numerous LAB strains to screen the most appropriate and effective LAB for each purpose.According to the circumstances of their isolated sources, LAB can be roughly classified into two groups: one is from animal sources, such as raw milk, cheese, or intestine, and the other is from plant sources, such as grasses, vegetables, or fruits. Animal-derived LAB have been traditionally used for fermented foods, such as yogurt and cheese. On the other hand, plant-derived LAB are used for Japanese traditional fermented dishes and miso. Lactococcus (Lc.) lactis, Lactobacillus (Lb.) bulgaricus, and Streptococcus salivarius subsp. thermophilus are typical animal-derived LAB. Lb. plantarum and Lb. brevis are representatives of plant-derived LAB. But, it is also true that Lc. lactis was isolated from many kinds of flowers (unpublished data). We insist that plant-derived LAB, in general, must be more resistant to rigorous environments than animal-derived LAB. Indeed, the plant-derived LAB strains newly isolated by our group, Lb. plantarum SN13T, SN35N, and Lb. brevis 925A, were found to be more viable in artificial gastric fluid and bile than animal-derived LAB, like Lc. lactis, Lb. bulgaricus, and Lb. acidophilus (unpublished data). Our previous clinical study has demonstrated that the yogurt made by Lb. plantarum SN13T improves constipation, serum lipid levels, and liver function more efficiently than the yogurt made by animal-derived LAB.11) It is known that even the same species of LAB show different probiotic properties. Considering the advantage of plantderived LAB resistant to digestive fluids in gastrointestinal tract, it will be significant to screen various plant-derived LAB strains which show excellent probiotic activities.Gastrointestinal mucosa is the primary site of antigen invasions. The gut-associated lymphoid tissue (GALT) is composed of Peyer's patches, peripheral lymphoid tissues, and the appendix. The GALT plays an important role in the immune system of the gastrointestinal tract.12,13) Immunoglobulin A (IgA) is the most abundant in the body of all immunoglobulin isotypes as well as the predominant immunoglobulin isotype in the mucosal surface of the gastrointestinal tract.12,14) Peyer's patch, where IgA is produced by plasma cells, is considered as the most important defense site in intestinal immunity to prevent microbial invasion.
15-18)The effect of probiotics on intestinal immunity has been investigated using laboratory animals; IgA assessments were conducted using isolated inte...