Antibody response of calves to immunoaffinity-purified bovine respiratory syncytial virus VP70 after vaccination and challenge exposure

Lynn D. Nelson From the Department of Veterinary Science, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0905.

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Clayton L. Kelling From the Department of Veterinary Science, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0905.

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Gary A. Anderson From the Department of Veterinary Science, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0905.

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Summary

Immunoaffinity-purified bovine respiratory syncytial virus (brsv) fusion (F) protein elicited anti-brsv-specific antibody responses in brsv-seronegative calves. After primary vaccination, all calves seroconverted to brsv as determined by the virus neutralization (vn) test and developed anti-F protein antibodies detectable by protein immunoblot analyses. Subsequent vaccinations induced > twofold increase in vn titer in 3 of 9 (33%) calves, and 1 calf became vn-negative, but still had nonneutralizing antibody detectable by protein immunoblot analysis. This calf remained seronegative after challenge exposure.

Two groups of calves were vaccinated im with immunoaffinity-purified brsv F protein. Each dose was 2 ml containing 20 μg of purified F protein. Freund's adjuvants were used for all vaccinations, with Freund's complete adjuvant used for the primary vaccination and Freund's incomplete adjuvant for subsequent vaccinations. The vaccine was administered to both groups at weeks 0 and 3; the first group received a third vaccination at week 21. Group-1 and -2 vaccinated calves and non-vaccinated contact controls were intranasally aerosol challenge-exposed with low cell culture-passage brsv on weeks 22 and 9, respectively.

Eight of 9 vaccinated calves did not develop a humoral anamnestic response following challenge exposure, as demonstrated by vn test and protein immunoblot analyses. Calf 14 from group 1 which had a 1:2 vn antibody titer prior to vaccination, was the only calf that developed an anamnestic response. This suggests that vaccine-induced antibodies interfered with the immune response or that the challenge virus (and the virus that calf 14 was infected with before challenge exposure) contained different F protein epitopes, compared with the purified F protein immunogen.

Summary

Immunoaffinity-purified bovine respiratory syncytial virus (brsv) fusion (F) protein elicited anti-brsv-specific antibody responses in brsv-seronegative calves. After primary vaccination, all calves seroconverted to brsv as determined by the virus neutralization (vn) test and developed anti-F protein antibodies detectable by protein immunoblot analyses. Subsequent vaccinations induced > twofold increase in vn titer in 3 of 9 (33%) calves, and 1 calf became vn-negative, but still had nonneutralizing antibody detectable by protein immunoblot analysis. This calf remained seronegative after challenge exposure.

Two groups of calves were vaccinated im with immunoaffinity-purified brsv F protein. Each dose was 2 ml containing 20 μg of purified F protein. Freund's adjuvants were used for all vaccinations, with Freund's complete adjuvant used for the primary vaccination and Freund's incomplete adjuvant for subsequent vaccinations. The vaccine was administered to both groups at weeks 0 and 3; the first group received a third vaccination at week 21. Group-1 and -2 vaccinated calves and non-vaccinated contact controls were intranasally aerosol challenge-exposed with low cell culture-passage brsv on weeks 22 and 9, respectively.

Eight of 9 vaccinated calves did not develop a humoral anamnestic response following challenge exposure, as demonstrated by vn test and protein immunoblot analyses. Calf 14 from group 1 which had a 1:2 vn antibody titer prior to vaccination, was the only calf that developed an anamnestic response. This suggests that vaccine-induced antibodies interfered with the immune response or that the challenge virus (and the virus that calf 14 was infected with before challenge exposure) contained different F protein epitopes, compared with the purified F protein immunogen.

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