M. tuberculosis demonstrates an extraordinary penetrance of the human population. Much of its success is liked to its ability to persist within the host, which is dependent on the formation of granulomas, or localized infections that support bacterial persistence without overt disease. The granuloma fulfills functions ambivalent to the host because although it limits spread of the infection it also provides a haven for the bacterium from the more extreme rigors of the host immune response. Dr. Russell proposes to extend his existing studies into the life cycle stages of M. tuberculosis by studying how both the host and the bacterium initiate and maintain the granuloma in both the murine and human infections.
The specific aims of the proposal are: 1. Characterization of the bacterial factors that induce and modulate granuloma development. M. tuberculosis synthesize and release 7 major lipids these lipids induce granuloma-like structures in mice and stimulate a pro-inflammatory response in macrophages in culture. These lipids will be identified structurally and their biological activities delineated. 2. Elucidation of the roles of host cytokines, chemokines and their receptors in the biology of the granuloma. The ability of the cell wall lipids to induce granuloma in non-immune and immune mice will be determined and compared with bacterial granulomas. Bacterial lipid granulomas will be dissected in an in vivo model that mixes labeled macrophages from relevant knock-out mice with the lipid-bearing particles and the data compared to immunohistological analysis of murine tuberculosis granulomas. The PI will also develop an in vitro cell migration model to determine the cytokines and chemokines responsible for recruitment of macrophages to the infection foci. 3. Examination of human alveolar macrophages from BAL cells from tuberculosis patients. These studies will encompass functional characterization of BAL macrophages for phagocytosis, vacuolar acidification and cellular responsiveness. The PI will also examine the cytokine/chemokine profiles of these cells as well as whether or not they contain mycobacterial cell wall constituents. The BAL cells will also be examined in cell migration assays based on the result from the murine granuloma model described in aim # 2.
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