Oral Administration of Lactobacillus pentosus Strain S-PT84 Enhances Anti-Influenza Virus-Specific IgG Production in Plasma after Limited Doses of Influenza Virus Vaccination in Mice

Background: It has been reported that various Lactobacillus species enhance antigen-specific antibody production after viral infection and/or vaccination in animals and humans. In this study, the effect of oral administration of Lactobacillus pentosus strain S-PT84 on subcutaneous administration of limited dose of 2.5 ng of influenza A virus (IAV) (H1N1) split hemagglutinin (HA) vaccine was studied in mice. Methods: Seven-week-old BALB/c female mice were fed the AIN-93M diet with or without 0.186% S-PT84 for 6 weeks ad libitum and then given subcutaneous injection of IAV/California/7/2009 (H1N1) HA vaccine at doses of 2.5–15.0 ng/mice and boosted on day 28. Two weeks after the last vaccination, the mice were sacrificed under anesthesia, and the amount of anti-HA-specific IgG in plasma was measured by ELISA. Results: The levels of anti-HA-specific IgG in plasma were significantly higher in the S-PT84 group than in the control group without S-PT84 treatment. Anti-HA-specific IgA levels in nasal washes were under the detection level in both groups. Conclusion: Oral administration of S-PT84 enhanced the production of HA-specific IgG antibody in plasma after subcutaneous vaccination, even at the limited dose of 2.5 ng of IAV (H1N1) HA in mice, suggesting that S-PT84 has a potent adjuvant activity against IAV HA.