Effects of lactobacilli on parameters of non-specific resistance of mice

The viability of Lactobacillus plantarum in vivo and the effects of viable and heat-killed lactobacilli on parameters of non-specific resistance were studied. After intravenous administration of 10(8) viable lactobacilli, which is a dose with optimal adjuvant activity, viable lactobacilli could be isolated from spleens for more than 1 week and from livers and lungs for more than 3 weeks. Both viable and heat-killed lactabacilli stimulated the clearance of colloidal carbon, viable bacteria stimulated initially to a higher extent. Doses of 10(8) viable and heat-killed lactobacilli, but not less, stimulated non-specific resistance to Listeria monocytogenes and caused splenomegaly. Doses as small as 10(5) viable and heat-killed lactobacilli induced substantial natural killer (NK) cell activity in the peritoneal exudate 4 days after i.p. administration. Higher doses generally caused a dose-dependent increase of NK cell activity. Viable lactobacilli injected in the paw and to a lesser extent heat-killed bacteria caused a proliferative response in the draining popliteal lymph node, which peaked at day 5. Results are discussed in relation to adjuvanticity and comparisons are made with bacterial agents already used in immunotherapy.