Abstract
The nature of the antibody response of cattle to the antigen of Yersinia enterocolitica IX cross-reacting with Brucella spp. was examined. Density-gradient ultracentrifugation, ion-exchange chromatography, antibody adsorption and elution and disulphide bond reduction tests showed that both 19 S IgM and 7 S IgG(1) and IgG(2) antibodies were produced in response to the cross-reacting antigen. The highest titres of cross-reacting antibodies were detected by the agglutination and Coombs antiglobulin tests. Production of complement-fixing and precipitating antibodies cross-reacting with Br. abortus was transient and high titres were not attained.In contrast, although infection with Br. abortus also evoked cross-reacting antibodies of the IgM and IgG classes, much higher titres were produced in the complement fixation and precipitation tests and these persisted for long periods. At all stages of the serological response to both organisms, the two infections could be differentiated by the quantitative Rose Bengal plate test.