Horse allergy: Curly Horses can mediate immune tolerance

Abstract

American Bashkir Curly Horses are claimed to be hypoallergenic, but this has not been clinically proven. In the present study, the effect of exposure to Curly Horses was investigated in 141 patients allergic to horses by measuring their lung function and nasal patency during Curly Horse contact. Continuous contact with Curly Horses, including riding and brushing, decreased the allergic ridersʼ reactivity as measured by FEV1, PEF, and PNIF. Subsequent visits (up to 40 or more hours of riding) further reduced reactivity to the Curly Horses. Allergic events to horses occurred only in 72 out of 1312 riding hours, mainly in the first ten riding hours.In 41 out of the 141 patients, it was further investigated whether repeated exposure to Curly Horses could induce tolerance to other horses. Patients in the tolerance induction study were tested annually for horse allergy using a nasal provocation test. The tolerance induction study showed that exposure to Curly Horses induced immune tolerance to other horses in 88% of patients who completed the study.To understand the mechanism causing hypoallergenicity, we performed IgE immunoblots to determine whether Curly Horse hairs contain IgE binding proteins. However, no differences in IgE reactivity were found between Curly and non-Curly Horses. Moreover, the immune tolerance induction study patients did not show decreased IgE reactivity to hairs from Curly or non-Curly Horses even though patients had developed tolerance. However, we did find increasing levels of anti-horse IgG antibodies in the study patients.Overall, our data strongly suggests that continuous exposure to Curly Horses can induce immune tolerance, rendering these patients non-reactive to horses. The reason for the reduced clinical allergenicity of Curly Horses remains unclear, but the data suggest that blocking IgG antibodies may be of importance for immune tolerance development.

Hypoallergenic animals: A promise of hope for allergic patients?

“…A clinical study enrolling 41 patients with horse allergy to a tolerance induction protocol including regular riding 1 of 4 Curly Horses (treatment group, n = 27) found that 12 out of 12 participants of the treatment group who completed the study had a negative NPT [ 30 ]. However, a total of 15 participants in the treatment group withdraw before the end of the study and 12 of those had a positive NPT.…”

“…An important drawback of the study is that it only included a control group of patients with low exposure to Curly Horse (n = 14; < 7 riding hours/year), but no control group exposed to non-Curly horse riding. Notably, patients who had longer periods of riding (> 20 hours) and whose symptoms disappeared, initially had mild symptoms [ 30 ]. In order to provide scientific evidence of the Curly Horse to be hypoallergenic, a broader clinical study involving a treatment group and a control group riding non-Curly horses has to be designed, including a categorization by symptom scores and IgE profiling of patients as well as a determination of allergen content of the horses those patients are exposed to.…”