Immunohistochemical investigation of CD14 in experimental rabbit pneumonic pasteurellosis

Abstract

The present study investigated the immunolocalization of CD 14 and the bacterial antigen of Pasteurella multocida serotype A :3 in normal and pneumonic rabbit lungs. To induce pneumonia, P. multocida serotype A :3 (4 x 10(6) CFU/ml) was inoculated intra-tracheally to twelve New Zealand White rabbits (Oryctolagus cuniculus) at age of 8-10 weeks while four rabbits received physiologic saline with the same route. Nine infected rabbits died with clinical sings of the disease between the 3(rd) and 13(th) days post inoculation. On day 14, the remaining three infected and control rabbits were euthanatized. The histopathological evaluation of the lung samples collected from nine infected rabbits with clinical symptoms revealed severe cases of fibrinopurulent and necrotic pneumonia and fibrinopurulent pleuritis. The bacterial antigen was immunolocalized in macrophages and degenerating leukocytes around the necrotic tissue and in exudates occupying the lumens of bronchia, bronchioles, and alveoli. CD14 immunoreactivity was present in alveolar macrophages, neutrophiles, alveolar epithelial cell surfaces, and lumens of the capillaries of the pneumonic lungs. In three rabbits, inoculated but presenting no clinical symptoms and no histopathological lesions, the bacterial antigen was found in the alveolar wall; however, like in the controls, CD14 immunoreactivity was present only in the lumen of capillaries. Double labelling immunohistochemistry indicated that CD14 was closely associated with the bacterial antigen in inflamed regions of the lung. Results suggested that interaction of the bacterial antigens and CD14 may have a critical role in lung pathologies resulting from P. multocida serotype A :3 infection.