Enhanced susceptibility to Trichuris muris infection of B10Br mice treated with the probiotic Lactobacillus casei.

The aim of this paper was to establish a suitable model for exploring the immunoregulatory bases of the interaction of probiotics with intestinal helminth infections. The mouse whipworm Trichuris muris, was used in the susceptible B10Br mice. Mice were treated orally with either viable or dead probiotic L. casei and 1 week later they were submitted to a challenge infection of 400 embryonated eggs of T. muris. Treatment with either viable or dead bacteria significantly increased the intestinal worm burden by day 22 post-infection. Viable L. casei significantly reduced the levels of faecal IgA induced by challenge infection. The proliferation response of MNL cells against mitogens was significantly reduced by dead bacteria and abrogated by viable bacteria. Furthermore the presence of the probiotic was associated to a significant decrease in IFN-gamma, TNF-alpha, IL-4 and Il-13 with no effect on IL-5 in both MNL and PP with regard to challenge control infection. The presence of L. casei did not significantly modify the proportion of CD4(+) and CD8(+) cells in both MLN and PP. In summary, in the susceptible B10Br mouse strain the presence of probiotic L. casei is associated to an increased susceptibility to infection by the intestinal whipworm T. muris. The mechanisms underlying this evidence could be related to the deactivation of TNF-alpha dependent Th2 effector responses against T. muris due to the strong down-regulation of this cytokine that is induced by the probiotic agent.