Cell-mediated immune responses in cattle vaccinated with a vaccinia virus recombinant expressing the nucleocapsid protein of rinderpest virus

Rinderpest virus (RPV) is a member of the genus Morbillivirus in the family Paramyxoviridae which causes an acute and often fatal disease in large rum inants, To examine the immune response to the virus nucleocapsid (N) protei n, a recombinant vaccinia virus expressing RPV nucleocapsid protein (rVV-RP V-N) was used to vaccinate cattle. The recombinant vaccine induced low leve ls of nonneutralizing anti-N antibodies. RPV-specific cell-mediated immunit y induced by the recombinant was assessed by measuring both the lymphocyte proliferation and cytotoxic T-lymphocyte responses. The protective immune r esponse was examined by challenging the vaccinated cattle with either a hig hly virulent (Saudi 1/81) or a mild (Kenya/eland/96) strain of the virus. T he 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 mil d strain, apart from a transient fever, no clinical signs of rinderpest inf ection were seen in the vaccinated cattle. One out of two control cattle sh owed a similar response but the other died from classic rinderpest disease. Virus-neutralizing antibodies were induced more quickly following challeng e 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 chall enge with a virulent strain of the virus. Protection was seen in one of thr ee animals challenged with a mild strain of the virus; however, a greater n umber of animals would need to be tested to estimate the significance of th e protection afforded by the N protein.