A preventive immunization approach against insect bite hypersensitivity: Intralymphatic injection with recombinant allergens in Alum or Alum and monophosphoryl lipid A.

This study examines a potential immunization approach to prevent insect bite hypersensitivity (IBH) in horses. The research tested the effectiveness of using recombinant allergens with aluminum hydroxide (Alum) alone or combined with monophosphoryl lipid A (MPLA). The study found that both methods led to an increase in protective antibodies and suggests this could be a promising strategy for preventing and treating IBH.

Understanding Insect Bite Hypersensitivity (IBH)

• IBH is an IgE-mediated dermatitis in horses, primarily triggered by the bites of Culicoides insects.
• These insects are not native to Iceland, so Icelandic horses that have been exported to areas with Culicoides insects are often affected by IBH.

The Immunization Approach

• The study involved vaccinating twelve healthy Icelandic horses intralymphatically three times with 10 μg each of four recombinant Culicoides nubeculosus allergens either in Alum alone or in Alum in combination with MPLA.
• Recombinant allergens are those which have been produced in a lab, typically using genetic engineering. Alum and MPLA are adjuvants – substances that enhance the body’s immune response to an antigen.

Results of the Study

• Administering the allergens in both Alum and Alum/MPLA resulted in a significant increase in specific IgG subclasses and IgA against all recombinant allergens. There were no significant differences observed between the groups that had been injected with the two different adjuvants.
• In addition, the antibodies created as a result of the vaccinations in both groups were able to block the binding of allergen-specific IgE from IBH-affected horses to a similar extent.
• There were no IgE-mediated reactions induced, suggesting that the vaccination was safe and did not lead to hypersensitivity in the horses.
• Allergen-stimulated PBMC (peripheral blood mononuclear cells) from horses that had received Alum/MPLA, but not those that received Alum only, produced substantially more IFNγ (interferon gamma) and IL-10 (interleukin 10) than PBMCs from non-vaccinated control horses. These are types of cytokines, cell signalling proteins that help coordinate immune responses.

Conclusion

• The study concluded that intralymphatic administration of small amounts of purified allergens in Alum/MPLA incites a high IgG antibody response and a Th1/Treg immune response. Consequently, this could be a promising approach for both preventing and treating IBH in horses.