Bacillus toyonensis amplifies the immunogenicity of an experimental recombinant tetanus vaccine in horses.

Overview

• This study investigated how supplementing horses with the probiotic Bacillus toyonensis affects their immune response to a recombinant tetanus vaccine.
• The results showed that horses receiving B. toyonensis had a stronger antibody response and increased immune cell activity compared to controls.

Introduction and Background

• Probiotic microorganisms, like Bacillus toyonensis, can stimulate immune responses and potentially improve vaccine effectiveness.
• Bacillus toyonensis is a nonpathogenic, Gram-positive bacterium used as a probiotic in animal feed that has demonstrated immunomodulatory effects across species.
• The focus of this study was to test the impact of B. toyonensis supplementation on immune responses in horses vaccinated with a recombinant tetanus toxin from Clostridium tetani.

Study Design and Methodology

• Twenty horses were divided into two equal groups (10 horses each):
• Supplemented group: Fed daily with B. toyonensis spores mixed in molasses for 42 days, starting 7 days before the first vaccination.
• Control group: Fed with molasses only (no probiotic), following the same timeline.
• All horses received two doses of the recombinant tetanus vaccine, spaced 21 days apart.
• Serum samples were collected to measure humoral immune responses using an in-house indirect ELISA for specific antibodies (IgG and its subtypes IgGa and IgGT) against the recombinant tetanus antigen.
• Peripheral blood mononuclear cells (PBMCs) were extracted to assess cytokine gene expression via quantitative PCR (qPCR) after stimulation with either B. toyonensis or the vaccine antigen.

Key Findings on Antibody Responses

• The group supplemented with B. toyonensis showed significantly higher antibody titers against the recombinant tetanus toxin:
• ELISA values were four times greater in the supplemented group compared to controls (p < 0.05).
• Higher levels of IgG sub-isotypes IgGa and IgGT were also observed in the supplemented horses, indicating a stronger and more diverse humoral response.

Immune Cell Cytokine Responses

• PBMCs from supplemented horses displayed notable increases in cytokine mRNA transcription after stimulation with B. toyonensis:
• IL1 increased by 15-fold, indicating heightened pro-inflammatory signaling.
• TNFα increased 8-fold, supporting enhanced immune activation.
• IL10 and IL4, involved in anti-inflammatory and helper T cell functions, increased 7- and 6-fold respectively.
• When PBMCs were stimulated with the tetanus vaccine antigen, supplemented horses showed:
• 1.6-fold increase in IL1 transcription.
• 1.8-fold increase in TNFα transcription.
• A slight decrease (0.5-fold) in IL4 transcription compared to controls.

Conclusions and Implications

• Supplementation with B. toyonensis significantly enhanced both the antibody-mediated (humoral) and cytokine-mediated immune responses to an experimental recombinant tetanus vaccine in horses.
• The probiotic appears to modulate immune cell activity, promoting a stronger response to vaccination.
• This suggests that using B. toyonensis as a dietary supplement could be a promising strategy to improve vaccine efficacy in horses and potentially other animals.
• Such findings support the growing interest in probiotics as immunomodulatory agents that can boost protective immunity during vaccination protocols.