INCREASED EXPRESSION OF VASCULAR CELL-ADHESION MOLECULE-1 BY THE AORTIC ENDOTHELIUM OF RABBITS WITH PASTEURELLA-MULTOCIDA PNEUMONIA

Vascular cell adhesion molecule-1 (VCAM-1) is expressed by endothelial cells in a variety of inflammatory conditions in experimental animals and humans. It is increased in rabbit endothelium after the intraveno us administration of endotoxin, after cholesterol feeding, in regenera tion after injury, and in alloxan-induced diabetes mellitus. The effec t of a respiratory tract infection with Pasteurella multocida, a commo n laboratory pathogen in rabbits, on VCAM-1 expression by aortic endot helial cells and on the endothelial ultrastructure was examined in spe cific-pathogen-free (SPF) New Zealand White rabbits infected by the in stillation of a suspension of live organisms into the nose and in conv entionally raised rabbits with naturally acquired P. multocida infecti on. Age-matched SPF rabbits maintained in a disease-free environment w ere controls. Rabbits were euthanized 50 days after infection, the aor ta was excised, and the endothelial cells expressing VCAM-1 were ident ified by immunohistochemistry. Perfusion-fixed aortas from infected an d SPF rabbits were prepared for examination by electron microscopy. Al l infected animals had pneumonitis and leukocytosis. In SPF rabbits th e total leukocyte count was highest at postinfection day 25. There was a significant (P < 0.05) increase in the number of VCAM-1-positive ao rtic endothelial cells in infected SPF rabbits (34 +/- 4/10(4) endothe lial cells; n = 5) and rabbits with naturally acquired infection (57 /- 14/10(4) endothelial cells; n = 5) compared with control animals (1 2 +/- 3 per 10(4) endothelial cells; n = 4). The endothelium of infect ed rabbits had morphologic alterations consistent with injury. Thus in fection at remote sites can activate arterial endothelium and induce t he expression of VCAM-1.