Insect bite hypersensitivity (IBH) is an allergic
dermatitis of horses caused by
bites of midges (Culicoides spp.).
IgE-mediated reactions are often involved in the pathogenesis of this disease. IBH does not occur in Iceland due to the absence of Culicoides, but it occurs with a high frequency in Icelandic horses exported to mainland Europe, where Culicoides are present. We hypothesize that immunization with the Culicoides
allergens before export could reduce the incidence of IBH in exported Icelandic horses. The aim of the present study was therefore to compare intradermal and intralymphatic vaccination using four purified recombinant
allergens, in combination with a Th1 focusing adjuvant. Twelve horses were vaccinated three times with 10μg of each of the four recombinant Culicoides nubeculosus
allergens. Six horses were injected intralymphatically, three with and three without IC31(®), and six were injected intradermally, in the presence or absence of IC31(®). Antibody responses were measured by immunoblots and ELISA, potential sensitization in a sulfidoleukotriene release test and an intradermal test,
cytokine and FoxP3 expression with real time PCR following in vitro stimulation of PBMC. Immunization with the r-
allergens induced a significant increase in levels of r-
allergen-specific
IgG1,
IgG1/3,
IgG4/7, IgG5 and
IgG(T). Application of the r-
allergens in IC31(®) adjuvant resulted in a significantly higher
IgG1,
IgG1/3,
IgG4/7
allergen-specific response.
Intralymphatic injection was slightly more efficient than
intradermal injection, but the difference did not reach significance. Testing of the blocking activity of the sera from the horses immunized intralymphatically with IC31(®) showed that the generated
IgG antibodies were able to partly block binding of serum
IgE from an IBH-affected horse to these r-
allergens. Furthermore,
IgG antibodies bound to
protein bands on blots of C. nubeculosus salivary gland extract. No
allergen-specific
IgE was induced and there was no indication of induction of
IgE-mediated reactions, as horses neither responded to Culicoides extract stimulation in a sulfidoleukotriene release test, nor developed a relevant
immediate hypersensitivity reaction to the recombinant
allergens in skin test.
IL-4 expression was significantly higher in horses vaccinated intralymphatically without IC31(®), as compared to horses intradermally vaccinated with IC31(®). Both routes gave higher
IL-10 expression with IC31(®). Both intralymphatic and intradermal vaccination of horses with recombinant
allergens in IC31(®) adjuvant induced an immune response without adverse effects and without
IgE production. The horses were not sensitized and produced
IgG that could inhibit
allergen-specific
IgE binding. We therefore conclude that both the injection routes and the IC31(®) adjuvant are strong candidates for further development of immunoprophylaxis and
therapy in horses.