Augmentation of host defense against Listeria monocytogenes infection by oral administration with polysaccharide RBS (RON).

Protection against Listeria monocytogenes in mice was enhanced by oral administration with a 30 mg/kg/day dose of polysaccharide RBS for 10 days. In mice treated with RBS, an enhanced elimination in vivo of L. monocytogenes was observed at the relatively late phase of listerial infection in correlation with enhanced immune responses against L. monocytogenes. The peritoneal macrophages from mice treated with RBS exhibited an increased activity of accessory cells for immune responses as assessed by production of interleukin-1 and antigen presentation to Listeria-immune T-cells. An increased activity of macrophages acting as accessory cells for immune responses may play important roles in the enhanced resistance against L. monocytogenes in mice treated orally with RBS.