Active immunity and T-cell populations in pigs intraperitoneally inoculated with baculovirus-expressed transmissible gastroenteritis virus structural proteins

The intraperitoneal inoculation of pigs with baculovirus-expressed transmissible gastroenteritis virus (TGEV) structural proteins (S, N, M) in conjunction with thermolabile Escherichia coli mutant toxin (LT-R192G) in incomplete Freund’s adjuvant (IFA) was tested in an attempt to elicit active immunity to TGEV in gut-associated lymphoid tissues (GALT). Four groups of 63 (1–5-week-old) suckling, TGEV-seronegative pigs were used to assess the efficacy of the recombinant protein vaccine (group 3) in comparison with sham (group 1), commercial vaccine (group 2), and virulent TGEV Miller-strain-inoculated pigs (group 4). The TGEV-specific mucosal and systemic immune responses were measured after in vivo and in vitro stimulation with TGEV-antigens. The major T-cell subset distribution was analyzed in vivo and in vitro after stimulation of mononuclear cells with TGEV (from mesenteric lymph nodes of group 3 inoculated with TGEV-recombinant proteins). Induction of active immunity was assessed by challenge of pigs with virulent TGEV at 27 days of age. Baculovirus-expressed TGEV proteins coadministered with LT-R192G in IFA induced mesenteric lymph node immune responses associated with IgA-antibodies to TGEV and partial protection against TGEV-challenge. The high titers of serum IgG- and virus-neutralizing-antibodies to TGEV in group 3 pigs most likely reflected the dose of TGEV S-protein administered. At the day of TGEV-challenge, the in vitro stimulation of mononuclear cells from the mesenteric lymph nodes of group 3 pigs with inactivated TGEV resulted in an increase in double positive (CD4+CD8+), natural killer (CD2+CD4−CD8+dim) and cytotoxic (CD2+CD4−CD8+bright) T-cell phenotypes, accompanied by increased expression of interleukin-2 receptor and a decrease of the null (CD2−CD4−CD8−/SW6+) cell phenotype.