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Infection and Immunity, November 1998, p. 5196-5201, Vol. 66, No. 11
Department of Microbiology and Immunology,
The University of Texas Medical Branch, Galveston, Texas 77555-1070
Received 13 May 1998/Returned for modification 9 June 1998/Accepted 18 August 1998
Lipoprotein (LP) is a major component of the outer membrane of
bacteria in the family Enterobacteriaceae. LP induces
proinflammatory cytokine production in macrophages and lethal shock in
LPS-responsive and -nonresponsive mice. In this study, the release of
LP from growing bacteria was investigated by immuno-dot blot analysis. An immuno-dot blot assay 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-logarithmic growth, approximately 1 to 1.5 µg of LP per ml was detected in culture supernatants from E. coli. In contrast, these culture supernatants contained 5 to 6 µg/ml of lipopolysaccharide (LPS). LP release was not unique to
E. coli. Salmonella typhimurium, Yersinia
enterocolitica, and two pathogenic E. coli strains
also released LP during in vitro growth. Treatment of bacteria with the
antibiotic ceftazidime significantly enhanced LP release. Culture
supernatants from 5-h cultures of E. coli were shown to
induce in vitro production of interleukin-6 (IL-6) by macrophages
obtained from LPS-nonresponsive C3H/HeJ mice. In contrast, culture
supernatants from an E. coli LP-deletion mutant were
significantly less efficient at inducing IL-6 production in C3H/HeJ
macrophages. 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 associated with gram-negative bacterial infections.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Lipoprotein Release by Bacteria: Potential Factor
in Bacterial Pathogenesis
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, The University of Texas Medical Branch, Galveston, TX 77555-1070. Phone: (409) 772-4917. Fax: (409) 747-6869. E-mail: gklimpel{at}utmb.edu.
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