Aus der Arbeitsgruppe Immunologie der Tierärztlichen Hochschule ...

7. Summary
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Christine Kobelt: Summer eczema, a type I allergy in Islandic horses: Kinetics of in
vivo-sensitisation of basophilic granulocytes monitored by means of
a functional in vitro test (FIT)
In this study Islandic horses raised and kept under different conditions and of different age,
with and without clinical symptoms sweet itch (summer eczema) were tested at various
seasons for their degree of sensitisation by means of a functional in vitro test (FIT) developed
by Susanne Kaul (1998).
Focus was put on following questions to be answered:
1. What about the type I sensitisation in horses, raised and living in an area without
Culicoides spp. (Iceland) ?
Twelve adult horses, born and living in Iceland, were studied: They showed measurable
amounts of immunoglobulins on the surface of their basophils, capable of inducing a
degranulation. All of them were “generally” sensitised with functional antibodies. This is the
main precondition for the ability to react with a type I hypersensitivity. Four of the tested
horses reacted strongly positive with allergen preparations derived from different insects,
excluding Culicoides nubeculosus.
Upon challenge with different doses of Culicoides nubeculosus allergen 2 additional horses
out of the twelve showed borderline but clear positive reactions. This might be due to cross
reactivities with originary icelandic insects (such as Simulium spp.), for sweet itch inducing
Culicoides spp. do not exist in Iceland. Whether these cross reactions might indicate a cross
sensitization resulting in enhanced susceptibility to sweet itch once exported to Culicoides
areas could be elucidated by exposing them to Culicoides midges.
2. How long will horses with sweet itch stay detectably sensitised, when kept in a
Culicoides free region for a longer period of time (Spiekeroog) ?
Even after 15 years on Spiekeroog without any clinical signs 17 affected horses still proved a
clearly positive sensitisation of their basophils against Culicoides nubeculosus. They did not
loose the principle ability to redevelop sweet itch upon new antigen contact, even after a long
time (up to 15 years tested). Furthermore, all of the 26 examined horses showed a “general”
sensitisation, due to the existence of antibodies capable of inducing a degranulation upon