Aujeszky's disease vaccination and infection of pigs with maternal immunity: effects on cell- and antibody-mediated immunity.

SCC, ADV-SCC, ADV-ADCC and ADV-LYST as well as ND50-titres of neutralizing serum antibodies were examined in 36 passively immune pigs, 25 of which were vaccinated at 3 weeks of age and partly revaccinated 3 weeks later. Twenty-five vaccinated animals and 8 non-immune control pigs were challenged with infectious ADV. Independent of the state of maternal immunity the cytotoxic response of the white blood cells from all the animals was low at WPP 3 but rose with increasing age. ADV-LYST occurred only in some of the animals. A single vaccination evoked no significant effect on our immune parameters, but revaccination led to higher ADV-LYST and ADV-ADCC. In pigs vaccinated at WPP 3 the neutralizing serum titres decreased gradually, similar to unvaccinated animals, indicating that the antibodies were of maternal origin. However, after vaccination at WPP 6, no further decline of ND50-titres could be detected, pointing to a limited antibody production. Animals vaccinated at WPP 3 and revaccinated 3 weeks later showed a significant increase of serum neutralizing titres. Whereas the controls showed typical symptoms of Aujeszky's disease, the immune animals, especially the unvaccinated passively immune pigs, showed only elevated temperatures and most of them excreted small amounts of ADV. The development of cellular immunity after infection was rather similar within the maternally immune group independent whether the animals had been vaccinated or not, but ADV-ADCC and ADV-LYST showed a more rapid progress within the vaccinated group than in the non-vaccinated group and the non-immune control group. Infection resulted in significantly higher ND50 titres in vaccinated and revaccinated animals than in unvaccinated animals, indicating a secondary response in those pigs. Thus, ADV sensitization of lymphocytes had been evoked by vaccination despite the presence of maternal antibody. The interpretation of the results was complicated by great individual and litter-dependent variations of the immune parameters.