MOLECULAR-CLONING, CHARACTERIZATION, AND TISSUE DISTRIBUTION OF RAT LIPOPOLYSACCHARIDE-BINDING PROTEIN - EVIDENCE FOR EXTRAHEPATIC EXPRESSION

LPS binding protein (LBP) is a glycoprotein present in normal serum th at becomes markedly elevated during acute phase responses. LBP has bee n reported to greatly potentiate host responses to endotoxin or LPS. T herefore, LBP may play a critical role in the body's response to injur y and infection. Little is known about the factors regulating producti on of LBP. To investigate the regulation of LBP expression, we have cl oned the full-length cDNA for rat LBP. The deduced amino acid sequence of rat LBP was highly homologous with that reported for rabbit and hu man LBP. The sequence of rat LBP further refines the conserved regions found within the family of proteins that bind LPS; this family is com prised of bactericidal permeability-increasing protein and LBP from mu ltiple species. Use of the rat LBP cDNA clone for Northern blot analys is reveals that LBP mRNA levels are markedly up-regulated in liver dur ing acute phase responses. However, in contrast to previous reports, w e also find evidence of extrahepatic expression of LBP under these ind uced conditions. The presence of LBP mRNA in activated tissues other t han liver suggests that LBP may play a larger role in local tissue res ponses to LPS than previously appreciated.