Immune response to nucleocapsid protein of turkey coronavirus and its protective efficacy in turkeys
Abstract
Nucleocapsid (N) protein was investigated as a candidate viral antigen with which to develop DNA and subunit vaccines against TCoV. Turkeys inoculated twice with the recombinant N protein developed N protein-specific lymphocyte proliferation responses and N protein-specific interferon-γ (IFN-γ) activity. These results indicate the presence of an active cell mediated immune response. Turkeys were inoculated thrice with a DNA vaccine encoding the TCoV N gene (pTriEX-N). DNA vaccination induced N protein-specific cell mediated immunity after the second booster. This was evident by a significant increase in N protein-specific blood lymphocyte proliferation and increased IFN-γ activity (P<0.05). Turkeys receiving three doses of N gene had a slight reduction in TCoV immunofluorescence in intestinal sections after challenge, indicating partial protection against TCoV enteritis. A prime-boost strategy was investigated as a mean of enhancing the efficacy of N gene vaccination. Turkeys were immunized with the DNA vaccine pTriEX-N and boosted twice with recombinant N protein formulated with ISCOMs™. Turkeys with such treatment compared to those vaccinated with pTriEX-N once or those boosted with recombinant N protein without ISCOMs had a significant increase in N protein-specific blood lymphocyte proliferation and in IFN-γ activity (P<0.05). The prime-boost strategy resulted in a significant reduction in the immunofluorescence to TCoV in intestinal sections after challenge. The adjuvant effects of calreticulin (CRT) in enhancing immunity to N gene were investigated in the context of the DNA vaccine. A DNA vaccine encoding an N-terminal fusion of TCoV N gene with turkey CRT was constructed (pTriEX-CRT-N). When compared to control groups, turkeys receiving pTnEX-CRT-N had a significant increase in N protein-specific blood lymphocyte proliferation and increased N protein-specific IFN-γ activity (P<0.05). Inclusion of CRT in the construct was found to enhance N protein-specific cell mediated immunity and significantly reduce TCoV in the intestines after challenge. In all studies there was a gradual increase in antibody response to N protein. However, there was no virus neutralizing activity. In conclusion, the prime-boost strategy using ISCOMs, or the inclusion of CRT in the DNA vaccine enhanced the N protein-specific cell mediated immunity and improved protection, although partial against TCoV challenge.
Degree
Ph.D.
Advisors
Wu, Purdue University.
Subject Area
Veterinary services|Anatomy & physiology|Animals|Zoology
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