Antigenicity of bovine milk xanthine oxidase in guinea pigs

Six female and four male albino guinea pigs were immunized with active purified xanthine oxidase of bovine milk mixed with equal volume of Freund's complete adjuvant. One male and one female were immunized with heat-inactivated xanthine oxidase mixed with equal volume of adjuvant. Two males and four females were controls and received a phosphate buffer mixed with equal volume of adjuvant. The mixtures were administered intradermally and subcutaneously at weekly intervals for 6 consecutive wk and blood samples collected weekly. The enzyme was antigenic by the coated tanned red blood cell method. After the third weekly immunization, precipitating antibodies were in the sera of animals that received the active enzyme. Hemagglutination titers increased during subsequent weeks and reached a maximum after the sixth weekly immunization. Antisera from animals immunized with heat-inactivated xanthine oxidase gave a positive response similar to that with animals immunized with the active enzyme. However, when the same antisera were tested with sheep red blood cells coated with heat-inactivated enzyme, no hemagglutination was observed. Ouchterlony double gel-diffusion tests showed that it may be possible to differentiate between antibodies elicited to active and heat-inactivated xanthine oxidase.