IMMUNOHISTOLOGICAL EVALUATION ON RESPIRATORY LESIONS OF PIGS INTRANASALLY INOCULATED WITH ACTINOBACILLUS-PLEUROPNEUMONIAE SEROTYPE-1

Nine-week-old pigs were inoculated intranasally with 6.10 x 10(3) (gro up 10(3)), 10(5) (group 10(5)) and 10(7) (group 10(7)) colony-forming unit of Actinobacillus pleuropneumoniae (App) serotype 1 designated HA -337 strain, respectively. One pig in group 10(5) and 2 pigs in group 10(7) died with dispnea and hemorrhagic pleuropneumonia within 20 to 4 8 hr post inoculation (PI). All pigs necropsied on 7 days in groups 10 (5) and 10(7) had focal fibrous pleuropneumonia. Histologically, pulmo nary lesions were classified into three stages; peracute, acute and su bacute. Fatal cases in group 10(7) had peracute lesion composed of sev ere edema, hemorrhage and necrobiosis of alveoli, with mononuclear cel ls infiltration in the dilated interlobulus. The fatal case in group 1 0(5) had acute pulmonary lesion composed of focal or linear infiltrati on of round and fusiform cells that frequently showed swirling pattern in alveoli. The surviving cases in group 10(5) and 10(7) had subacute lesion composed of multifocal pulmonary necrosis surrounded by fibrou s tissue. The swirling pattern was clearly seen in demarcation zone. I mmunohistochemically, App antigens scattered as intact bacteria in alv eoli, dilated interlobular septa and pleura, and lymph vessels in pera cute and acute lesions. Areas of necrosis were also stained weakly. Al though no antigen was detected in cytoplasm of macrophages and infiltr ated cells in peracute lesions, App antigen was detected as positively stained mass in cytoplasm of some macrophages in acute lesions. In su bacute lesions, App antigens were recognized as intact bacteria in nec rotic areas and among the swirling pattern cells of demarcation zone. Macrophages had App antigens as a large mass of pigment in the cytopla sm in area of fibrosis.