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.Bacillus anthracis is a gram-positive, spore-forming bacterium that causes the disease anthrax. The infectious B. anthracis spore is a dormant, metabolically inactive form of the organism made up of distinct, concentric layers that collectively provide a highly structured casing capable of protecting the spore core from high temperature, UV irradiation, lytic digestion, and numerous reactive agents (31, 59). Spore germination is initiated through receptor-mediated interactions between soluble germinant molecules (typically nutrients such as single amino acids, sugars, or purine nucleosides) and germinant receptors located at the inner membrane of the dormant spore (20,36). Although the molecular mechanism(s) linking germinant binding to the loss of dormancy is undefined, germinant receptor engagement initiates a cascade of processes, including dipicolinic acid (DPA) release, that promote core rehydration and result in the controlled degradation of the protective spore structures; as germination concludes, metabolic activity resumes, and vegetative outgrowth is initiated (58). Fully virulent B. anthracis bacilli generate several virulence factors including an antiphagocytic, poly-D-glutamic acid capsule encode...