Bacillus anthracis, the causative agent of inhalational anthrax, enters a host through the pulmonary system before disseminating throughout the body. Our previous work has shown that human alveolar macrophages play a critical role in the initial innate immune response to B. anthracis spores through cell signal-mediated cytokine release. We propose that the lung epithelia also play an important role in the innate immune response to pathogens, and we have developed a human lung slice model to study this process. Exposure of our lung slice model to B. anthracis (Sterne) spores caused rapid activation of the mitogen-activated protein kinase signaling pathways ERK, P38, and JNK. This was followed by an increase in mRNA of several cytokines and chemokines. This was reflected on a translational level with a peak fold increase of TNF-α, IL-6, IL-8, MIP-1α, and the MCP-1 protein of 25, 3, 9, 34, and 5, respectively, as determined by ELISA. Inhibition of individual pathways by the signaling inhibitors UO126, SP 600125, and SB 0203580 was not sufficient to block induction of chemokines and cytokines to background levels. When the three inhibitors were combined, induction of IL-6 and IL-8 was completely blocked and of MCP-1 and MIP-1α was partially blocked. Taken together, these data show activation of pulmonary epithelium in response to B. anthracis spore exposure. Thus, the lung epithelia actively participate in the innate immune response to B. anthracis infection through cell signal-mediated elaboration of cytokines and chemokines.
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