THE BIPHASIC MESSENGER-RNA EXPRESSION PATTERN OF BOVINE INTERLEUKIN-8IN PASTEURELLA-HAEMOLYTICA LIPOPOLYSACCHARIDE-STIMULATED ALVEOLAR MACROPHAGES IS PRIMARILY DUE TO TUMOR-NECROSIS-FACTOR-ALPHA

Pasteurella haemolytica serotype 1 is the bacterial agent responsible for the pathophysiological events associated with bovine pneumonic pas teurellosis. Our previous studies support a role for the lipopolysacch aride (LPS) from P. haemolytica in the induction of proinflammatory cy tokines. One of the pathological hallmarks of bovine pneumonic pasteur ellosis is an influx of neutrophils into the alveolar spaces. This pro nounced influx suggests the local production of a chemotactic factor(s ) such as interleukin-8 (IL-8). In the context of the lung, the alveol ar macrophage appears to be the major producer of IL-H, a proinflammat ory cytokine with potent neutrophil chemotactic activity. By using Nor thern blot analysis, we have examined the kinetics of IL-8 mRNA expres sion in P. haemolytica LPS-stimulated bovine alveolar macrophages and found that I ng of LPS per mi induces maximal expression of IL-8 mRNA. The results also indicate a biphasic time course expression pattern i n which IL-8 mRNA levels peak between 1 and 2 h in the first phase and between 16 and 24 h in the second phase (P < 0.01). In addition, mono specific polyclonal antibodies were used to demonstrate the role of tu mor necrosis factor alpha (TNF-a) in the second phase of IL-8 mRNA exp ression. Our findings support a role for P. haemolytica LPS and TNF-al pha in the induction of IL-8 from bovine alveolar macrophages.