Previously identified 39-, 50-, and 76-kd integral outer membrane proteins (IOMP) of Actinobacillus pleuropneumoniae, a respiratory tract pathogen, were separated by electroelution of sodium dodecyl sulfate-polyacrylamide gel electrophoresis-obtained fragments and their role in opsonophagocytosis by porcine leukocytes was investigated by flow cytometry of fluorescein-labeled A pleuropneumoniae. Using specific antisera, immunoblot analysis indicated that the 3 proteins were antigenically distinct. Antibodies against each IOMP have an important role as opsonins for phagocytosis by porcine leukocytes. The effect of using a combination of an 3 of the specific antisera was minimal. Antiserum absorbed against intact A pleuropneumoniae and Escherichia coli organisms indicated that the antibodies to the 39-, 50-, and 76-kd IOMP were specific for A pleuropneumoniae antigens. Nonheat-treated antiserum did not increase phagocytosis, compared with heat-inactivated antiserum, indicating that complement may not have a major role in opsonization of A pleuropneumoniae.

Monoclonal antibodies were prepared against 40- and 56- to 64-kd antigens of Chlamydia pecorum strain Maeda, which was isolated from a cow with pneumonia. Using the monoclonal antibodies, 5 strains of C pecorum, 25 strains of mammalian and 19 strains of avian C psittaci, 1 strain of C pneumoniae, and 3 strains of C trachomatis were analyzed for immunologic reactivity by use of the indirect immunofluorescent test. Monoclonal antibody analysis revealed immunologic relatedness between C pecorum and mammalian strains of C psittaci, which were completely differentiated from the other avian strains. Bovine strains were distinguished from ovine strains. Antigenic diversity mm observed for bovine and ovine strains. Feline- and guinea pig-derived strains were shown to be immunologically different from bovine and ovine strains. Results provide the basis for typing and epidemiologic study of bovine and ovine strains of C pecorum and C psittaci.