A NOVEL ESCHERICHIA-COLI LIPID A MUTANT THAT PRODUCES AN ANTIINFLAMMATORY LIPOPOLYSACCHARIDE

A unique screen was used to identify mutations in Escherichia coli lip id A biosynthesis that result in a decreased ability to stimulate E-se lectin expression by human endothelial cells. A mutation was identifie d in the msbB gene of E. coli that resulted in lipopolysaccharide (LPS ) that lacks the myristoyl fatty acid moiety of the lipid A. Unlike al l previously reported lipid A mutants, the msbB mutant was not conditi onally lethal for growth, Viable cells or purified LPS from an msbB mu tant had a 1000-10,000-fold reduction in the ability to stimulate E-se lectin production by human endothelial cells and TNF alpha production by adherent monocytes. The cloned msbB gene was able to functionally c omplement the msbB mutant, restoring both the LPS to its native compos ition and the ability of the strain to stimulate immune cells. Nonmyri stoylated LPS acted as an antagonist for E-selectin expression when mi xed with LPS obtained from the parental strain. These studies demonstr ate a significant role for the myristate component of LPS in immune ce ll activation and antagonism. In addition, the msbB mutant allowed us to directly examine the crucial role that the lipid A structure plays when viable bacteria are presented to host defense cells.