Targeting eosinophils by active vaccination against interleukin-5 reduces basophil counts in horses with insect bite hypersensitivity in the 2nd year of vaccination

This research reviews an active vaccination against interleukin-5 (IL-5) in horses, utilized to reduce basophil counts in equines with a condition known as insect bite hypersensitivity (IBH). The study, conducted over three years, shows that the vaccine also decreased eosinophil amounts in the blood of horses, indicating it had an additional effect on diminishing basophil levels.

Study Overview

• The focus of this research is the development and analysis of an equine vaccine targeting interleukin (IL)-5, a molecule involved in the immune response.
• Previously, self-vaccinations using virus-like particles (VLPs) presenting IL-5 or IL-31 antigens have been suggested for the treatment of insect bite hypersensitivity (IBH), a seasonal recurrent allergic dermatitis in horses.

Vaccine Effectiveness

• The vaccination trial extended over three years, with horses receiving a placebo in the first year and the IL-5 targeting vaccine in the following two years.
• Similar to human monoclonal antibodies targeting IL-5 or the IL-5 receptor alpha (IL-5Rα), the equine vaccine targeting IL-5 was successful in significantly reducing blood eosinophil counts in horses.
• Eosinophils are a type of white blood cell that play a key role in the body’s immune responses, particularly in combating parasites and in the occurrence of allergic reactions. By reducing their number, the vaccine effectively decreases the inflammatory reaction in horses with IBH.

Bystander Effects of the Vaccine

• Besides reducing eosinophil counts, the study also found that there was a decrease in the number of basophils – another type of white blood cells that play a crucial role in allergic reactions.
• However, this reduction in basophil counts was observed only in the third year of the study, suggesting a bystander effect of the anti-IL-5 vaccine.
• Here, a bystander effect refers to an indirect effect where the vaccination against IL-5, although not directly targeting basophils, nevertheless led to their reduction in number. This finding suggests that suppressing IL-5 seems to non-specifically influence other aspects of the immune response.