LIPOPROTEIN RELEASE BY BACTERIA - POTENTIAL FACTOR IN BACTERIAL PATHOGENESIS

Lipoprotein (LP) is a major component of the outer membrane of bacteri a in the family Enterobacteriaceae, LP induces proinflammatory cytokin e production in macrophages and lethal shock in LPS-responsive and -no nresponsive mice. In this study, the release of LP from growing bacter ia was investigated by immune-dot blot analysis. An immune-dot blot as say that could detect LP at levels as low as 100 ng/ml was developed. By using this assay, significant levels of LP were detected in culture supernatants of growing Escherichia coli cells. During mid-logarithmi c growth, approximately 1 to 1.5 mu g of LP per ml was detected in cul ture supernatants from E. coli. In contrast, these culture supernatant s contained 5 to 6 mu g/ml of lipopolysaccharide (LPS). LP release was not unique to E. call. Salmonella typhimurium, Yersinia enterocolitic a, and two pathogenic E. coli strains also released LP during in vitro growth. Treatment of bacteria with the antibiotic ceftazidime signifi cantly enhanced LP release. Culture supernatants from 5-h cultures off . coil were shown to induce in vitro production of interleukin-6 (IL-6 ) by macrophages obtained from ITS-nonresponsive C3H/HeJ mice. In cont rast, culture supernatants from an E. coli LP-deletion mutant were sig nificantly less efficient at inducing IL-6 production in C3H/HeJ macro phages. These results suggest, for the first time, that LP is released from growing bacteria and that this released LP may play an important role in the induction of cytokine production and pathologic changes a ssociated with gram-negative bacterial infections.