Summary auto-generated
Researchers investigated whether vaccinating cattle with a recombinant vaccinia virus expressing rinderpest virus (RPV) nucleocapsid protein could induce protective immunity. Two experiments were conducted: in Experiment I, vaccinated cattle challenged with a highly virulent RPV strain developed disease similarly to unvaccinated controls, though with a slight delay in symptom onset. In Experiment II, cattle vaccinated with the same recombinant were challenged with a mild RPV strain; two of three vaccinated animals showed only transient fever while one control animal died from classic rinderpest disease. The vaccine induced cell-mediated immunity evidenced by lymphocyte proliferation and cytotoxic T-lymphocyte responses. Following challenge with the mild strain, vaccinated cattle produced virus-neutralizing antibodies more rapidly than controls. However, the nucleocapsid protein-based vaccine failed to protect against virulent RPV challenge. The authors conclude that while cell-mediated immunity induced by the nucleocapsid protein can accelerate antibody production upon virus exposure, this response is insufficient for protection against highly virulent strains, though some protection may occur against milder virus variants.
Key findings
- Vaccination with nucleocapsid protein recombinant failed to protect cattle against challenge with virulent RPV, though it slightly delayed disease onset compared to unvaccinated controls.
- Against mild RPV strain challenge, vaccinated cattle showed minimal clinical signs (only transient fever in 2/3 animals) while one control animal died, suggesting possible partial protection.
- The vaccine induced RPV-specific cell-mediated immunity including lymphocyte proliferation and cytotoxic T-cell responses, with minimal neutralizing antibody production pre-challenge.
- Vaccinated cattle mounted faster virus-neutralizing antibody responses following mild strain challenge compared to unvaccinated controls, indicating N-protein-primed T-cells enhanced subsequent B-cell responses.
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Abstract
Rinderpest virus (RPV) is a member of the genus Morbillivirus in the family Paramyxoviridae which causes an acute and often fatal disease in large ruminants. To examine the immune response to the virus nucleocapsid (N) protein, a recombinant vaccinia virus expressing RPV nucleocapsid protein (rVV-RPV-N) was used to vaccinate cattle. The recombinant vaccine induced low levels of non-neutralizing anti-N antibodies. RPV-specific cell-mediated immunity induced by the recombinant was assessed by measuring both the lymphocyte proliferation and cytotoxic T-lymphocyte responses. The protective immune response was examined by challenging the vaccinated cattle with either a highly virulent (Saudi 1/81) or a mild (Kenya/eland/96) strain of the virus. The vaccinated cattle were not protected against challenge with the virulent RPV strain, except they showed a slight delay in the onset of disease when compared with the unvaccinated controls. In cattle challenged with the mild strain, apart from a transient fever, no clinical signs of rinderpest infection were seen in the vaccinated cattle. One out of two control cattle showed a similar response but the other died from classic rinderpest disease. Virus-neutralizing antibodies were induced more quickly following challenge with the mild strain in vaccinated cattle compared to the control animals. These data suggested that the cell-mediated immunity induced by rVV-RPV-N could stimulate the rapid production of neutralizing antibodies following RPV challenge but this response was not sufficient to protect against challenge with a virulent strain of the virus. Protection was seen in one of three animals challenged with a mild strain of the virus; however, a greater number of animals would need to be tested to estimate the significance of the protection afforded by the N protein.