Serum and mucosal antibody isotype responses to M-like protein (SeM) of Streptococcus equi in convalescent and vaccinated horses.

The research article focuses on comparing the antibody response against equine strangles in horses that have recovered from infection and those vaccinated against it. The study finds that while the commercial vaccine stimulates similar serum antibody responses, it does not trigger a mucosal response, suggesting the importance of mucosal immunity in resistance against the disease.

Objective

The primary objective of this study was to understand the various differences between the Streptococcus equi-specific antibody responses in convalescent, or recovered, horses and those vaccinated with a commercial strangles vaccine.

Methodology

• The researchers focused on the M-like protein (SeM) of Streptococcus equi. The protein is anti-phagocytic and serves as an important protective antigen.
• The researchers assessed the presence and levels of IgA and IgG sub-antibodies in the serum and mucosal samples from both vaccinated and convalescent horses. They were particularly interested in specific serum IgGc and opsonophagocytic IgA levels.

Results

• The results indicated that specific opsonophagocytic IgGb was the predominant antibody in horses vaccinated intramuscularly and those recently recovered from infection.
• The infections also triggered high levels of specific opsonophagocytic serum IgGa during and shortly after infection, while vaccination stimulated only low-level serum IgGa.
• Very low levels of specific serum IgGc and opsonophagocytic IgA were present post-infection or vaccination.
• Interestingly, during the acute and convalescent phases of infection, a significant mucosal antibody response was noted. This was not practiced in vaccinated horses.
• IgGb was generally predominant in the nasopharyngeal washings during the acute phase but was replaced by specific IgA during convalescence.

Conclusion

In a nutshell, the findings revealed that while vaccination induces SeM-specific serum isotype responses similar to those seen in convalescence, it failed to stimulate mucosal responses. This observation is significant as it indicates the potentially essential role of mucosal immunity in the acquired resistance to equine strangles, a disease that continues to cause significant economic losses in the equine industry, despite the availability of commercial vaccines.