Selection for immune response in goats: the effect of immunization procedure on antibody response to diphtheria toxoid and human serum albumin

The serum antibody titers to diphtheria toxoid and human serum albumin were determined in 103 goat kids from lines selected for 12 yr for high or low antibody response to diphtheria toxoid. In the 12th yr, six groups of kids were immunized with different preparations of the antigens. In all groups but one, the antigens were emulsified in Freund's incomplete adjuvant with added sonicated Mycobacterium paratuberculosis. The groups received the following treatments: Group 1 was immunized with both antigens mixed in the same syringe, Group 2 got both antigens injected separately, Group 3 got both antigens injected separately, but with a lower concentration of M. paratuberculosis, Group 4 was immunized with diphtheria toxoid only, Group 5 was immunized with human serum albumin only, and Group 6 was immunized with both antigens mixed, but without any M. paratuberculosis. The animals were immunized at 4 wk of age, and the antibody titers were determined 3 wk later by ELISA and passive hemagglutination. The mean antibody titers to both antigens were different between the selected lines (P less than .03). There was no effect of separate vs combined injections of antigens. However, there were indications of antigen suppression or competition between the antigens. Animals receiving only one antigen seemed to mount a higher antibody response to that antigen than did animals immunized with two antigens.