Regulation of interleukin-8 expression in porcine alveolar macrophages by bacterial lipopolysaccharide.
Interleukin (IL)-8 is a macrophage-derived neutrophil chemotactic factor that plays an important role in the recruitment of neutrophils to inflammatory loci. Hence, expression of IL-8 by alveolar macrophages may be a significant factor in host defense in the lung and in the pathogenesis of pneumonia in swine. To initiate molecular studies of IL-8 regulation in pigs, we cloned IL-8 cDNA and examined the regulation of its mRNA in alveolar macrophages. The porcine IL-8 cDNA consists of 1491 base pairs including a coding region of 309 base pairs. The deduced amino acid sequence was 75 and 81% similar to human and rabbit IL-8, respectively. Resting macrophages contained low levels of IL-8 mRNA, which increased markedly after exposure to bacterial lipopolysaccharide (LPS). LPS induction of IL-8 was direct, not mediated through elevation of tumor necrosis factor or interleukin-1. The effect of LPS on IL-8 expression was dose dependent, and induction was observed at a concentration of 10 pg/ml. IL-8 mRNA expression was detectable within 0.5 h after stimulation with LPS, peaked at 3-6 h at about 30-fold higher levels than in resting cells, and was maintained for 24 h. Secreted IL-8, measured by neutrophil chemotaxis, was induced within 4 h by LPS, and accumulated in the media throughout the 24-h period. The mechanism of induction of IL-8 mRNA appeared to involve transcription and RNA processing. Nuclear run-on analysis showed that the IL-8 gene was actively transcribed in noninduced cells; upon stimulation with LPS, the rate of IL-8 transcription was increased about 4-fold. A single mature mRNA species was detected by primer extension analysis. The half-life of IL-8 mRNA transcripts in aveolar macrophages was approximately 2 h and did not change after LPS stimulation. The ability of LPS to induce IL-8 expression was suppressed by recombinant human IL-4 and dexamethasone in a concentration-dependent manner. These observations indicate that the expression of IL-8 is an early event in the sequelae to bacterial infection in the lung.
Lin
G
G
Department of Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota, St. Paul 55108.
Pearson
A E
AE
Scamurra
R W
RW
Zhou
Y
Y
Baarsch
M J
MJ
Weiss
D J
DJ
Murtaugh
M P
MP
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013552:Swine; D014158:Transcription, Genetic
D018076:DNA, Complementary; D016209:Interleukin-8; D008070:Lipopolysaccharides; D015847:Interleukin-4; D003907:Dexamethasone