CHANGES IN THE LUNGS OF LAMBS AFTER INTRATRACHEAL INJECTION OF LIPOPOLYSACCHARIDE FROM PASTEURELLA-HAEMOLYTICA A1

Ten lambs aged 8 weeks were inoculated intratracheally through the tra cheal wall with lipopolysaccharide from Pasteurella haemolytica Al and examined in chronological sequence by light and electron microscopy f or pulmonary lesions. An acute fibrinopurulent pneumonia was produced, which resolved within 72 h but bore many resemblances to field cases of pneumonic pasteurellosis. Sequestration of neutrophils in the capil laries of the lungs and aggregation of surfactant in the alveoli occur red rapidly, followed by swelling of the alveolar and capillary endoth elia, oedema, haemorrhage, and emigration of neutrophils into the inte rstitium and small air spaces of the lungs. Necrosis of isolated neutr ophils was a constant feature. Alveolar, interstitial and intravascula r macrophages and lymphoid cells increased slowly to become the predom inant inflammatory cells at 72 h. A surprising feature was the transie nt appearance of multinucleated cells in the lungs ar. 2 and Gh after inoculation. It is concluded that lipopolysaccharide makes a major con tribution to the pathogenesis of P. haemolytica infection in the lungs of sheep.