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To investigate the antibody response after local application of lung-pathogenic bacteria, pigs were immunized with viable or inactivated Actinohacillus pleuropneumoniae by the oral and aerogenous route. After 3 weeks class-specific immunoglobulins against purified A. pleuropneumoniae capsular polysaccharides (CP) were determined in scrum and BALF by ELISA. A significant increase of IgA antibodies was found in BALF but not in sera of all immunized pigs. Oral immunization with viable A. pleuropneumoniae and aerosol immunization with either viable or inactivated bacteria resulted in a significant increase of IgG antibodies to the CP antigen in BALF, whereas only aerosol exposure to viable bacteria resulted in a significant increase in IgG antibodies in serum. A significant increase in anti-CP IgM in BALF was observed after aerosol exposure but not after oral immunization. IgM antibodies towards CP increased significantly by both routes of immunization with viable bacteria. The anti-CP activity of all three isolypesin sera and BALF was low in all groups compared with the positive controls, although inoculation of viable A. pleuropneumoniae led to higher levels of antibody concentration than inactivated bacteria. Our results indicate a traffic of primed lymphocytes from the gut into the bronchoalveolar airways and further support the hypothesis that polysaccharide-specific B cells may functionally mature at the mucosal surfaces. [ABSTRACT FROM AUTHOR]

The development of bronchus-associated lymphoid tissue (BALT) was investigated in the pig, which is a species in which BALT is not found constantly. Different routes of contact with a specifically lung-pathogen bacterium Actinobacillus (Haemophilus) pleuropneumoniae were tested. Pigs, selected by bacteriological screening methods and the number of granulocytes in the bronchoalveolar lavage (BAL), were infected by aerosol. They were compared to previously enterally immunized pigs using active and inactivated bacteria. The development of BALT after the infection was compared to that in pigs with a single enteral, or no, contact with the bacterium. BALT was less frequent in these groups than in the infected pigs. Previously immunized pigs developed the highest number and the largest BALT with the most prominent morphological signs of activation. Immunization with living or inactivated bacteria did not cause histological differences. BALT was preferentially located around bronchioli and small bronchi. Additional BALT predominantly occurred in the walls of larger bronchi. Definite compartments of T and B lymphocytes were not found in immunohistological studies of BALT. It was concluded that the development of BALT can be induced by different modes of microbial stimulation.