Epsilon Archive for Student Projects

Abstract

Bovine respiratory syncytial virus (BRSV) is one of the main pathogens in the bovine respiratory disease complex and has strong negative impact on animal welfare, farm production and economy. Vaccines against BRSV have been on the market since the 1970s but there are still challenges regarding vaccine efficacy, especially in presence of maternally derived antibodies (MDA) that inhibit immune responses to vaccine antigens in calves.

The aim of this master thesis was to evaluate the inhibitory effect of MDA on antibody responses against different mimotopes of the prefusion form of the BRSV fusion protein (Pre F) in calves. Four different vaccines that contained the BRSV nucleoprotein (N) as nanorings and either the whole Pre F (Pre F Full + N) or different compositions of F protein mimotopes 2, 4 and 5, an-chored on N (Pre F 2/4/5 + N, Pre F 2 + N and Pre F 5 + N), were evaluated in 24 calves with BRSV-specific MDA from a farm with previous BRSV outbreaks. The calves were divided in 4 groups of six calves, as equal as possible in terms of age and passive immunity (maternally de-rived BRSV-specific IgG in serum). The calves were vaccinated twice with 30 days interval (day 0 and 30). Serum samples were collected at -14, 0, 21, 30, 44 and 184 days pre-/post- first vaccina-tion. The humoral responses were evaluated through enzyme linked immunosorbent assays and serum neutralising tests (SN-test) for quantification of BRSV-, Pre F-, N- and Pre F mimotope 2 peptide-specific IgG in serum and the virus neutralising ability of the antibodies induced by the different vaccines. Attempts were made to measure Pre F mimotope 4- and 5-peptide specific IgG but the results were discarded due to unspecific binding.

The Pre F Full + N vaccine induced a significant increase in BRSV-specific IgG in serum after the second vaccination (between day 30 and day 44) and significantly higher titres of BRSV-specific IgG and serum neutralising antibodies compared to all the other vaccines on day 44. There was no significant decrease among any of the vaccinated calves in BRSV-specific IgG in serum after first vaccination and the IgG responses to BRSV N did not differ significantly between calves vaccina-ted with the different vaccines. The calves vaccinated with Pre F 2 + N had no significant increase BRSV-specific IgG antibody titre in serum after second vaccination and a significant decrease in SN-titres between day 44 and day 184.

The results suggest that all vaccines in the study were immunogenic and that the whole Pre F protein was superior in terms of inducing BRSV-specific and serum neutralising antibodies in the presence of MDA compared to the vaccines that contained F protein mimotopes 2, 4 and/or 5. This may be due to the wider variety of mimotopes in pre F Full compared to in the other vaccines, to a specific mimotope not present in any of the other vaccines or due to problems with the conforma-tion of mimotopes. Similar to other reports, antibodies targeting the N-protein and mimotope 2 of Pre F did not seem to have strong virus neutralising capability. Vaccines containing N protein + mimotopes 2, 4 and/or 5 elicited similar amounts of BRSV-specific IgG suggesting that MDA interfered with the antigens in these vaccines to a similar extent.

The Pre F subunit vaccine is an interesting candidate for vaccination of calves with passive im-munity. Further research on the humoral response in calves to BRSV pre F epitopes are relevant for the generation of further knowledge in this area.