Abstract
Lactobacillus casei Shirota (LcS), a strain of lactic acid bacteria, has been investigated for biological activity over many years. Recently it was revealed that LcS has potent antitumor and antimetastatic effects in rodents: An intrapleural injection of LcS effectively inhibits tumor growth in the thoracic cavity in mice, resulting in prolonged survival and an improved quality of life (QOL). These activities were dependent on the stimulation of the production of several cytokines such as interferon-γ, interleukin-12, and tumor necrosis factor-α. It was suggested that LcS induces a Thl response rather than a Th2 response. As a result of this action, the inhibition of ovalbumin-specific immunoglobulin E production in the LcS-treated group was evident, compared with the response in the control group. Also, an oral administration of LcS significantly delayed the onset of carcinogenesis in mice treated with 3-methylcholanthrene and restored T cell responses such as concanavalin A-induced T cell proliferation and interleukin-2 production. Moreover, it was demonstrated that an oral administration of LcS enhanced the natural killer cell activity of spleen cells. These observations indicate that LcS affects innate immunity and augments the natural resistance of the host. Taken together, the results suggest that LcS has the potential to ameliorate or prevent a variety of diseases through a modulation of the host's immune system, specifically cellular immune responses.
