Antimicrobial Effects of Interferon-Inducible CXC Chemokines against Bacillus anthracis Spores and Bacilli

Department of Medicine, Division of Infectious Diseases, University of Virginia Health Sciences System, Charlottesville, VA 22908, USA.
Infection and immunity (Impact Factor: 3.73). 02/2009; 77(4):1664-78. DOI: 10.1128/IAI.01208-08
Source: PubMed


Based on previous studies showing that host chemokines exert antimicrobial activities against bacteria, we sought to determine whether the interferon-inducible Glu-Leu-Arg-negative CXC chemokines CXCL9, CXCL10, and CXCL11 exhibit antimicrobial activities against Bacillus anthracis. In vitro analysis demonstrated that all three CXC chemokines exerted direct antimicrobial effects against B. anthracis spores and bacilli including marked reductions in spore and bacillus viability as determined using a fluorometric assay of bacterial viability and CFU determinations. Electron microscopy studies revealed that CXCL10-treated spores failed to undergo germination as judged by an absence of cytological changes in spore structure that occur during the process of germination. Immunogold labeling of CXCL10-treated spores demonstrated that the chemokine was located internal to the exosporium in association primarily with the spore coat and its interface with the cortex. To begin examining the potential biological relevance of chemokine-mediated antimicrobial activity, we used a murine model of inhalational anthrax. Upon spore challenge, the lungs of C57BL/6 mice (resistant to inhalational B. anthracis infection) had significantly higher levels of CXCL9, CXCL10, and CXCL11 than did the lungs of A/J mice (highly susceptible to infection). Increased CXC chemokine levels were associated with significantly reduced levels of spore germination within the lungs as determined by in vivo imaging. Taken together, our data demonstrate a novel antimicrobial role for host chemokines against B. anthracis that provides unique insight into host defense against inhalational anthrax; these data also support the notion for an innovative approach in treating B. anthracis infection as well as infections caused by other spore-forming organisms.

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    • "Additionally SIC interferes with the antibacterial activity of CXCL9, without disturbing its chemotactic activity (Egesten et al. 2007), suggesting that SIC interacts with the antimicrobial C-terminal region of CXCL9. Although CXCL9, CXCL10, and CXCL11 are interferon-g-inducible related chemokines that interact with the same CXCR3 receptor and have a similar antibacterial spectrum (Cole et al. 2001; Egesten et al. 2007; Yang et al. 2003; Crawford et al. 2009), the antimicrobial activity of CXCL10 and CXCL11 against E. coli, L. monocytogenes, and S. pyogenes is tenfold less than that of CXCL9 (Cole et al. 2001; Egesten et al. 2007). Analysis of the structures of CXCL10/IP-10 (Swaminathan et al. 2003), IP-10 mutant (NMeLeu27) (Booth et al. 2002), and CXCL11 (Booth et al. 2004) has shown that their C-terminal a-helices are smaller than the predicted C-terminal a-helix in CXCL9, which may account for the difference in the antimicrobial activities (Egesten et al. 2007; Eliasson and Egesten 2008). "
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