Biological effects of probiotics: what impact does Lactobacillus casei shirota have on us?

Probiotics have been defined as live bacteria beneficial to the host when administered in adequate amounts. To evaluate the effect of probiotics on the prevention of carcinogenesis, Lactobacillus casei Shirota (LcS) was given to the patients who had undergone the resection of superficial bladder cancer, and administration of LcS significantly reduced the recurrence rate of bladder cancer. When LcS was given to the patients whose colonic polyps were surgically removed, the recurrence of colorectal cancer with moderate or severe atypia was suppressed. To assess the putative actions of LcS on innate immune responses, we examined the effect of LcS on natural killer (NK) cell activity in humans. Daily ingestion of fermented milk containing LcS restored NK cell activity in healthy subjects with low NK cell activity as well as human T lymphotropic virus (HTLV)-1-associated myelopathy patients. When peripheral blood mononuclear cells from healthy humans were cultured in the presence of heat-killed LcS, NK cell activity was augmented, which were partly mediated by monocyte-derived interleukin (IL)-12. These findings suggest that LcS may help the reinforcement of our defense system against cancer by modulating innate immune functions.