Enhanced Antigen-Specific Delayed-Type Hypersensitivity and Immunoglobulin G2b Responses after Oral Administration of ViableLactobacillus casei YIT9029 in Wistar and Brown Norway Rats

ABSTRACT In this study, the effects of orally administered viableLactobacillus casei Shirota strain YIT9029 on the immunity parameters of Wistar and Brown Norway rats were examined. For this purpose, we used the Trichinella spiralis host resistance model. Two weeks before and during T. spiralisinfection, rats were fed 109 viable L. casei bacteria 5 days per week. The T. spiralis-specific delayed-type hypersensitivity (DTH) response was significantly enhanced in both Wistar and Brown Norway rats given L. casei. In both rat strains fedL. casei, serum T. spiralis-specific immunoglobulin G2b (IgG2b) concentrations were also significantly increased. In the model, no significant effects ofL. casei on larval counts or inflammatory reactions in the tongue musculature, body weights, or lymphoid organ weights were observed. Serum specific antibody responses, other than IgG2b, were not changed by feeding of L. casei. In contrast toL. casei, it was shown that orally administeredBifidobacterium breve or Bifidobacterium bifidum had no influence on the measured infection and immunity indices in the rat infection model. Since the rat DTH response is considered to be a manifestation of Th1 cell-mediated immunity and the IgG2b isotype has been associated with Th1 activity, it was concluded that Th1 cells could play an active role in the immunomodulatory effects of orally administered L. casei. Furthermore, our data do not indicate that the effect of oral supplementation withL. casei is dependent on the genetic background of the host.