Establishment of a protocol for preventive vaccination against equine insect bite hypersensitivity

Insect bite hypersensitivity (IBH) is a seasonal dermatitis of horses caused by IgE-mediated reactions to bites of Culicoides midges characterized by an imbalance of T-cell subsets. Iceland is free of the causative species but the prevalence of IBH in exported Icelandic horses is especially high. We have shown that intralymphatic (i.l.) vaccination with r-Culicoides allergens in Aluminum hydroxide (alum) and monophosphoryl lipid A (MPLA) adjuvants induces a desired Th1/regulatory T-cell response. The aim of this study was to compare i.l. to sub-cutaneous (s.c.) injection. Twelve healthy Icelandic horses were injected, i.l. or s.c., three times with four-week interval, using purified r-Culicoides allergens in alum/MPLA. Serum antibody levels and cytokine profile following in vitro re-stimulation of PBMC were analysed. Comparable allergen-specific IgG antibodies were induced following both routes of vaccinations. The antibodies showed similar capacity to block binding of IgE from IBH-affected horse to the allergens. Upon re-stimulation of PBMC, IL-10 was induced. Horses vaccinated i.l. produced more IFN-gamma and less IL-4 as compared to the horses injected s.c., but the difference did not reach significance. It can be concluded that applying the simpler s.c. injection instead of i.l. to obtain a suitable im-mune response could be option in IBH immunotherapy.

Automated summary

Insect bite hypersensitivity (IBH) is a seasonal dermatitis in horses caused by an imbalance of T-cell subsets. Vaccination with r-Culicoides allergens in Aluminum hydroxide and monophosphoryl lipid A adjuvants induces a desired Th1/regulatory T-cell response. This study compares intralymphatic (i.l.) and sub-cutaneous (s.c.) injection, and finds that both methods can induce allergen-specific antibodies and block the binding of IgE. Horses vaccinated i.l. produce more IFN-gamma and less IL-4 compared to those injected s.c. Ultimately, s.c. injection may be a viable option for IBH immunotherapy.