Pigs aerogenously immunized with genetically inactivated (ghosts) or irradiated Actinobacillus pleuropneumoniae are protected against a homologous aerosol challenge despite differing in pulmonary cellular and antibody responses

Aerosol immunization is a safe way to induce complete protection against pl europneumonia in pigs caused by the lung pathogenic bacterium Actinobacillu s pleuropneumoniae. In order to determine the local immune responses of vac ciness in concomitant with protection, lung lining fluid before and 3 weeks after immunization from pigs immunized three times with aerosols of either genetically inactivated ghosts which represent whole cell envelope prepara tions, or irradiated bacteria were examined following an homologous aerosol challenge. Specific antibody isotypes in the bronchoalveolar lavage were a ssayed by whole cell ELISAs. Total and relative numbers of cells including lymphocyte subsets were determined. In both vaccinated groups a net influx of plasma cells and lymphocytes, as well as a significant increase of speci fic IgG occurred. Concurrently, the CD4(+)/CD8(+) ratio was found to increa se after aerosol immunization. The lymphocyte subsets of IgG(+) and IgA(+) cells were found significantly higher in the group immunized with irradiate d bacteria when compared to pigs immunized with bacterial ghosts. The latte r group showed a significant increase of IgA, IgM, and a net influx of lymp hoid blasts and granulocytes in the bronchoalveolar lining fluid. Although differences between the local immune responses of both immunized groups occ urred, a significant increase of specific IgG and a net influx of plasma ce lls and lymphocytes were found to be associated with complete protection ag ainst a homologous aerosol challenge infection. (C) 1999 Elsevier Science B .V. All rights reserved.