Molecular cloning, expression and tissue distribution of canine lipopolysaccharide (LPS)-binding protein

The plasma lipopolysaccharide (LPS)-binding protein (LBP) plays an important role in infection caused by Gram-negative bacteria. It is markedly increased during acute-phase responses. In this study, we cloned the full length of canine LBP cDNA and determined its amino-acid sequence and its expression in several canine tissues. The isolated LBP cDNA contained a 1443-bp coding region, which encodes a 25-amino-acid signal peptide, a 456-amino-acid mature LBP and a stop codon, and a 3'-noncoding region containing a TATTTAT motif, which is probably involved in the degradation and/or suppression of mRNA translation. The amino-acid sequence of the mature canine LBP showed 78%, 66% and 67% identity with that of human, rat and rabbit LBPs, respectively. In transient expression assays, canine and human LBPs accelerated the production of tumor necrosis factor-alpha induced by LPS in human monocytes. Northern blot analysis showed that LBP mRNA is mainly expressed in the liver and kidneys of normal dogs. In situ hybridization analysis revealed that the canine LBP mRNA is mainly located in hepatocytes and in epithelial cells of the proximal urinary tubules of the kidneys. These findings suggest that LBP is produced in organs readily exposed to LPS, where it probably plays an important role in bacterial infections, particularly in those occurring after major surgery.