IMMUNE MODULATION OF BLOOD LEUKOCYTES IN HUMANS BY LACTIC-ACID BACTERIA - CRITERIA FOR STRAIN SELECTION

Lactic acid bacteria in food can transiently colonize the intestine an d exert beneficial effects (probiotic). Survival during intestinal tra nsit or adhesion to epithelium or both seem to be important for modify ing the host's immune reactivity. Because Lactobacillus acidophilus st rain La1 is adherent to enterocytes in vitro, we hypothesize that cont act with immune cells may occur in vivo. However, Bifidobacterium bifi dum strain Bb12, which shows high fecal colonization, is another poten tial immunomodulator. Twenty-eight volunteers were divided into two gr oups and given a fermented product containing one of the two strains. Lymphocyte subsets and leukocyte phagocytic activity were studied in b lood. No modifications were detected in lymphocyte subsets. In contras t, phagocytosis of Escherichia coli ssp. was enhanced in both groups ( P < 0.001 for both). Bacterial adhesion to enterocytes, fecal coloniza tion, or both seem to be valuable selection criteria for immunomodulat ion. Antiinfective mechanisms of defense can be enhanced after ingesti on of specific lactic acid bacteria strains.