Role of memory B-cell responses in serum and mucosal fluids of swine for protective immunity against pseudorabies virus.

We examined primary and memory isotype-specific antibody responses directed against pseudorabies virus in serum and mucosal fluids of pigs with and without passively acquired maternal antibody, and we studied the relationship between these responses and protection against virus challenge. Pigs were inoculated intranasally with the virulent NIA-3 strain or the avirulent Bartha strain, or they were inoculated IM with an inactivated vaccine containing the Phylaxia strain. Ten weeks later, all pigs were challenge-exposed intranasally with strain NIA-3. Only pigs that were without passively acquired antibody at the time they were inoculated with virulent virus appeared to have complete protective immunity against challenge exposure, as evidenced by lack of clinical signs of pseudorabies and lack of virus excretion. In contrast, pigs inoculated with strain Bartha or with the inactivated vaccine developed fever, had a period of growth arrest, and excreted virus after challenge exposure. In pigs without passively acquired antibody, intranasal inoculation with strains NIA-3 or Bartha was followed by primary IgM and IgA responses in serum and in oropharyngeal fluid as well as primary IgG1 and IgG2 responses in serum. Intramuscular inoculation with the inactivated vaccine induced primary serum IgM, IgG1, and IgG2 responses, but no mucosal responses. Challenge exposure of pigs that had been inoculated with the Bartha strain or the inactivated vaccine was followed by clear memory responses in serum and in oropharyngeal fluid. In contrast, challenge exposure of pigs that had been inoculated by the virulent NIA-3 strain was not followed by memory responses.(ABSTRACT TRUNCATED AT 250 WORDS)