Antihistamine activity in extracts of horse eosinophils.

Suspensions of horse eosinophils or the watery extracts of such suspensions were injected intraperitoneally into guinea-pigs. The eosinophils were obtained from 9 healthy cross-bred ponies. The number of eosinophils used for each injection varied between 20 and 300 millions. The guinea-pigs were exposed to a 0.6% histamine aerosol 1 to 8 hr later. The eosinophils of 5 ponies produced protection against the aerosol, the eosinophils of the other 4 ponies did not. Protection when produced did not last as long as 23 hr. The active principle in the watery extracts was stable, after freeze drying, for at least a few weeks.