Gene Expression of Primary Human Type I Alveolar Epithelial Cells Exposed to Bacillus anthracis, Sterne endospores

The lung is the entry site for Bacillus anthracis in inhalation anthrax, the most deadly form of the disease. Spores must escape through the alveolar epithelial cell (AEC) barrier and migrate to regional lymph nodes, germinate and enter the circulatory system to cause disease. Several mechanisms to explain alveolar escape have been postulated, and all these tacitly involve the AEC barrier. In this study, we incorporate our primary human type I AEC model, microarray gene profiling and gene enrichment analysis to study the response of AEC to B. anthracis, (Sterne) spores at 4 and 24 hours post-exposure. Spore exposure altered gene expression in AEC after 4 and 24 hours and differentially expressed genes (1.3 fold, p 0.05) included CCL4/MIP-1 (4 hours), CXCL8/IL-8 (4 and 24 hours) and CXCL5/ENA-78 (24 hours). Gene enrichment analysis revealed that pathways involving cytokine or chemokine activity, receptor binding, and innate immune responses to infection were prominent. Microarray results were confirmed by qRT-PCR and multiplex ELISA assays. Chemotaxis assays demonstrated that spores induced the release of biologically active neutrophil and monocyte chemokines, and that CXCL8/IL-8 was the major neutrophil chemokine. The small or sub-chemotactic doses of CXCL5/ENA-78, CXCL3/GRO and CCL20/MIP-3 may contribute to chemotaxis by priming effects. These data provide the first whole transcriptomic description of the human type I AEC initial response to B. anthracis spore exposure, and contribute to an increased understanding of the role of AEC in the pathogenesis of inhalational anthrax.

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