Viability and dose–response studies on the effects of the immunoenhancing lactic acid bacteriumLactobacillus rhamnosusin mice

Abstract

Previous studies have indicated that the lactic acid bacteriumLactobacillus rhamnosusHN001 can enhance immune function in mice, following oral delivery. However, the influence of bacterial cell viability on immunoenhancement, and the optimum dose of HN001 required for this effect, have not been determined. In the present study, both live and heat-killed preparations ofL. rhamnosusHN001 were shown to enhance the phagocytic activity of blood and peritoneal leucocytes in mice, at a dose of 109micro-organisms daily. In contrast, only live HN001 enhanced gut mucosal antibody responses to cholera toxin vaccine. Feeding mice with 107viable HN001/d for 14 d was shown to enhance the phagocytic capacity of blood leucocytes, with incremental enhancement observed at 109and 1011daily doses. In contrast, a minimum dose of 109viable HN001/d was required to enhance the phagocytic activity of peritoneal leucocytes, and no further increment was observed with 1011daily. This study demonstrates thatL. rhamnosusHN001 exhibits dose-dependent effects on the phagocytic defence system of mice, and suggests that while the innate cellular immune system is responsive to killed forms of food-borne bacteria, specific gut mucosal immunity may only be stimulated by live forms.