The isotype-specific antibody responses in serum and in nasal and pulmonary lavage fluids of swine following
aerosol immunization with an attenuated strain of Actinobacillus pleuropneumoniae serotype 1, strain CM5A, was investigated. The presence of
immunoglobulin G (
IgG),
IgA, and
IgM with specificities for capsular
polysaccharide,
lipopolysaccharide, and
hemolysin was determined by
enzyme-linked
immunosorbent assay by using purified
antigens. Strain CM5A induced serum
antibodies of each isotype to the three
antigens. The serum antibody response was sustained and typical of persistent antigenic stimulation. The specific
IgM response decreased and the specific
IgG response increased after challenge with strain CM5.
IgA specific for the three
antigens was detected in nasal secretions from all immune pigs, whereas specific
IgG could only be detected in samples contaminated with blood. Both
IgA and
IgG specific for each of the
antigens were detected in pulmonary lavage samples. There was no significant increase in specific
IgA in nasal secretions; however, levels of
lipopolysaccharide-specific and
hemolysin-specific
IgG and
IgA in pulmonary secretions rose after
aerosol challenge with strain CM5. Passive transfer of immune swine serum resulted in protection against
pleuropneumonia and in levels of specific serum
IgG which were similar to those in actively immunized pigs. It is concluded that specific serum
IgG antibodies are important in protection from porcine
pleuropneumonia.