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

The intraperitoneal inoculation of pigs with baculovirus-expressed transmis sible gastroenteritis virus (TGEV) structural proteins (S, N, M) in conjunc tion with thermolabile Escherichia coli mutant toxin (LT-R192G) in incomple te Freund's adjuvant (IFA) was tested in an attempt to elicit active immuni ty 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 effica cy of the recombinant protein vaccine (group 3) in comparison with sham (gr oup 1), commercial vaccine (group 2), and virulent TGEV Miller-strain-inocu lated pigs (group 3). The TGEV-specific mucosal and systemic immune respons es 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 aft er 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 I FA induced mesenteric lymph node immune responses associated with IgA-antib odies to TGEV and partial protection against TGEV-challenge. The high titer s of serum IgG- and virus-neutralizing-antibodies to TGEV in group 3 pigs m ost likely reflected the dose of TGEV S-protein administered. At the day of TGEV-challenge, the in vitro stimulation of mononuclear cells from the mes enteric lymph nodes of group 3 pigs with inactivated TGEV resulted in an in crease 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-CD-3-C D8-/SW6+) cell phenotype. (C) 1999 Elsevier Science B.V. All rights reserve d.