Oral Administration of Heat-Killed Lactobacillus gasseri OLL2809 Reduces Cedar Pollen Antigen-Induced Peritoneal Eosinophilia in Mice

Background: Lactobacillus gasseri OLL2809 strongly stimulates the production of interleukin (IL)-12 (p70) by innate immune cells. Thus, it is expected to ameliorate allergic diseases. We investigated whether the oral administration of heat-killed L. gasseri OLL2809 suppressed eosinophilia in cedar pollen antigen-challenged mice. Methods: BALB/c mice sensitized with Japanese cedar pollen extract were intraperitoneally challenged with the same extract. The mice were orally given heat-killed L. gasseri OLL2809 at doses of 0.5, 1, or 2 mg/day throughout the experimental period (21 d). After 24 hours of the challenge, the eosinophil number and cytokine levels in the peritoneal lavage fluid and the serum antigen-specific IgG levels were determined. Results: On administering varying amounts of heat-killed L. gasseri OLL2809, the number of eosinophils among the total number of cells was significantly reduced in all groups. In addition, the eosinophil number significantly decreased, and the eosinophil-suppression rate significantly increased by 44% in the 2-mg group. Although the serum immunoglobulin (Ig) G2a and IgG1 levels were not affected, the IgG2a/IgG1 ratio increased significantly in the 2-mg group compared with that of the control group. Furthermore, the administration of heat- killed L. gasseri OLL2809 resulted in the induction of IL-2 and reduction in granulocyte-macrophage colony- stimulating factor levels in peritoneal lavage fluid. Conclusions: We demonstrated that the oral administration of heat-killed L. gasseri OLL2809 suppresses eosinophilia via the modulation of Th1/Th2 balance. These observations suggested that heat-killed L. gasseri OLL2809 might potentially ameliorate the increased number of eosinophils in patients with Japanese cedar pollinosis