Targeting eosinophils by active vaccination against interleukin-5 reduces basophil counts in horses with insect bite hypersensitivity in the 2nd year of vaccination.
Authors: Rhiner Tanya, Fettelschoss Victoria, Schoster Angelika, Birkmann Katharina, Fettelschoss-Gabriel Antonia
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Insect bite hypersensitivity in horses represents a persistent challenge for equine practitioners, with limited effective immunomodulatory treatments currently available. Researchers investigated whether an active vaccine targeting interleukin-5 (IL-5) could reduce circulating eosinophil and basophil populations in affected horses, using a three-year trial design where horses received placebo in year one, followed by the eIL-5-VLP vaccine in years two and three. The vaccination produced marked reductions in blood eosinophil counts immediately after starting the vaccine, consistent with previous studies, whilst basophil counts decreased significantly but only emerged as a measurable effect in the third year of treatment—indicating a delayed, indirect mechanism rather than direct IL-5-mediated basophil suppression. These findings suggest the anti-IL-5 vaccine may work through both primary pathways and secondary bystander immunological effects that require prolonged activation to manifest fully. For practitioners managing IBH, this data supports the potential of IL-5-targeted vaccination as a multi-year therapeutic approach, though the delayed basophil response indicates that meaningful clinical assessment should extend beyond the first vaccination season to capture the full immunomodulatory benefit.
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Practical Takeaways
- •Active vaccination against IL-5 may offer a novel immunotherapeutic option for managing IBH in horses, with effects developing progressively over multiple vaccination seasons
- •The delayed basophil reduction suggests that extended vaccination protocols (beyond 2 years) may provide enhanced clinical benefit for allergic responses
- •This approach could reduce reliance on systemic corticosteroids or antihistamines for seasonal IBH management in susceptible horses
Key Findings
- •IL-5-targeting VLP vaccine significantly reduced circulating eosinophil counts in horses with IBH
- •Basophil count reduction occurred in the 3rd year of vaccination, suggesting a delayed bystander effect
- •Placebo administration in year 1 followed by active vaccination in years 2-3 demonstrated sustained immunological response
- •Anti-IL-5 vaccination effects paralleled outcomes of human monoclonal antibody therapies targeting IL-5 or IL-5Rα