Salmonella flagellin induces tumor necrosis factor alpha in a human promonocytic cell line.
During infection of the gastrointestinal tract, salmonellae induce cytokine production and inflammatory responses which are believed to mediate tissue damage in the host. In a previous study, we reported that salmonellae possess the ability to stimulate tumor necrosis factor alpha (TNF-alpha) accumulation in primary human monocytes, as well as in the human promonocytic cell line U38. In this model system, cytokine upregulation is not due to lipopolysaccharide but is mediated by a released protein. In the present study, TnphoA transposon mutagenesis was used to identify the TNF-alpha-inducing factor. A mutant Salmonella strain which lacks the ability to induce TNF-alpha was isolated from a TnphoA library. Genetic analysis of this mutant demonstrated that the hns gene has been interrupted by transposon insertion. The hns gene product is a DNA-binding protein that regulates the expression of a variety of unrelated genes in salmonellae. One of the known targets of histone-like protein H1 is flhDC, the master operon which is absolutely required for flagellar expression. Analysis of other nonflagellated mutant Salmonella strains revealed a correlation between the ability to induce TNF-alpha and the expression of the phase 1 filament subunit protein FliC. Complementation experiments demonstrated that FliC is sufficient to restore the ability of nonflagellated mutant Salmonella strains to upregulate TNF-alpha, whereas the phase 2 protein FljB appears to complement to a lesser extent. In addition, Salmonella FliC can confer the TNF-alpha-inducing phenotype on Escherichia coli, which otherwise lacks the activity. Furthermore, assembly of FliC into complete flagellar structures may not be required for induction of TNF-alpha.
Ciacci-Woolwine
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F
Department of Microbiology and Immunology, Wake Forest University Medical Center, Winston-Salem, North Carolina 27157, USA.
Blomfield
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IC
Richardson
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SH
Mizel
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SB
D002460:Cell Line; D004251:DNA Transposable Elements; D005408:Flagellin / Q000276:immunology / Q000494:pharmacology*; D006801:Humans; D008070:Lipopolysaccharides / Q000633:toxicity; D008262:Macrophage Activation; D012475:Salmonella / Q000276:immunology / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
D004251:DNA Transposable Elements; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D005408:Flagellin