DNA vaccine coding for glycoprotein B of PRV induces cytotoxic T cell responses in pigs against PRVE.M.A. van Rooija, B.L. Haagmansb, H.L. Glansbeekb, Y.E. de Vissera, W. Boersmaa and A.T.J. Bianchia
a Departments of Mammalian Virology and Immunology, Institute for Animal Science and Health, ID-DLO, Lelystad, The Netherlands
b Virology Unit, Department of Infectious Diseases and Immunology, Veterinary Faculty, Utrecht University, Utrecht, The Netherlands
Abstract - Vaccination based on naked DNA is regarded as an alternative to conventional vaccines because it combines the efficacy of attenuated vaccines with the biological safety of inactivated vaccines. Recently, we showed that vaccination with a cocktail of naked DNA coding for the immunorelevant glycoprotein B (gB), gC and gD of pseudorabies virus (PRV) induced both antibody and cell-mediated immunity in pigs and provided protection against challenge infection. To determine the role of the different glycoproteins in the induction of protective immune responses against PRV, we compared the efficacy of naked DNA coding for gB, gC and gD individually. Groups of 10-12 weeks old SPF pigs were vaccinated three times with an interval of 4 weeks between each vaccination. Pigs were vaccinated with g of plasmid carrying the gene coding for gB, gC or gD. Pigs vaccinated with g sham plasmid served as the sham-vaccinated control group. All pigs were vaccinated intradermally by syringe needles. Six weeks after the third vaccination, all pigs were challenged intranasally with 105 plaque forming units of the virulent wild type strain NIA3 per animal to assess protection. Animals were checked for humoral and cellular immune responses at regular intervals after vaccination. Virus excretion, body weight, fever and clinical signs were assessed after challenge infection. Pigs vaccinated with gB-DNA or gC-DNA developed moderate levels of neutralising antibodies whereas pigs vaccinated with gD-DNA developed high levels of virus neutralising antibodies. In contrast, pigs vaccinated with gB-DNA developed strong lymphoproliferation (LPT) responses whereas pigs vaccinated with gC-DNA or gD-DNA developed weak LPT responses. In addition, only pigs vaccinated with gB-DNA developed clear cytotoxic T cell responses, resulting in specific lysis of up to 50%. Both CD6 + and CD6 - T lymphocytes were involved in the cytolytic activity. All pigs vaccinated with gB-DNA or gD-DNA survived challenge infection whereas one out of six pigs vaccinated with gC-DNA and two out of six sham vaccinated pigs died. Pigs vaccinated with gD-DNA excreted virus for a significantly shorter period than pigs vaccinated with gB-DNA or gC-DNA. Pigs vaccinated with gB-DNA, however, had lower levels of viral peak excretion than pigs vaccinated with gC-DNA, gD-DNA or the sham vaccinated pigs. Based on the duration of fever and clinical signs, pigs vaccinated with gD-DNA were protected the best, followed by pigs vaccinated with naked DNA coding for gB. We have demonstrated that gB is important for the induction of cytolytic anti-PRV T cells and that gD is important for the induction of virus neutralising antibodies. Both glycoproteins protect against a challenge infection and form an attractive alternative for future anti-PRV DNA vaccines.
Corresponding author: E.M.A. van Rooij Fax: (31) 320 238668;
© INRA, EDP Sciences 2000