Factors influencing biometric potency assays of brucella allergens in guinea-pigs.

Procedures for the titration of brucella allergens in guinea-pigs were studied using “Brucellergen” and an allergen prepared from strain B 115, a rough strain of Br. melitensis. The most important factors influencing the biometric assay of brucella allergens were the method of sensitization and the total dose of allergen given to each animal. Maximum skin reactivity was observed in guinea-pigs which had been infected for 8 or more weeks with virulent Br. abortus strain 544. Animals infected with attenuated Br. abortus strain 19 showed maximum responses 3 weeks after infection which gradually decreased thereafter. Guinea-pigs sensitized with killed rough Br. abortus strain 45/20 in Freund's incomplete adjuvant developed a stable level of sensitivity which was lower than that induced by the virulent strain. A large dose of allergen (100 μg) killed some guinea-pigs which had been infected for 6 or more weeks with strain 544, and it depressed the skin reactivity of animals sensitized by the other methods. The response to any given dose of allergen was depressed if guinea-pigs were given other injection of allergen simultaneously. For the titration of unknown allergens, it is preferable to inject each ten-fold dilution singly into small groups of optimally sensitized animals. The smallest dose producing reactions from 15 to 20 mm in diameter should be selected as the quantity about which a second titration would be carried out with five-fold differences above and below, also given in single doses per animal.