**7. Conclusion**

The formation of lipid inclusions during infection in the host as well as in the pathogen during intracellular infection with *M. tuberculosis* and *M. leprae* plays an important role in pathogen‐ esis. A hallmark of intracellular infection is the formation of foamy macrophages. *M. tubercu‐ losis* and *M. leprae* induce the formation of lipid droplets in the host cell. The accumulated lipids are used as energy and carbon source. In fact *M. tuberculosis* seems to switch completely to fatty acid catabolism at the transition from the acute to the chronic phase of infection. The central role of fatty acid metabolism during the dormant state of *M. tuberculosis* is underlined by the finding that both isocitrate lyase, icl and icl2, are essential for intracellular replication in the lung [79,80]. The TAG metabolism and the resulting formation of lipid inclusions of host and pathogen play a fundamental role in infection. Indeed TAG-derived fatty acids from the host cell are imported into *M. tuberculosis* and incorporated into bacterial TAG [46]. In conclusion the enzymes involved in lipid droplet metabolism are essential for survival of the pathogen in the lung and thus attractive targets for novel drugs. Especially enzymes with DGAT activity such as Tgs and Ag85A seem to be promising drug target candidates. Another promising targets seem to be the recently discovered cell wall associated and secreted esterases, which are involved in the utilization of host cell lipids such as Rv0183 and LipY [55, 75,76]. Future studies should also focus on the lipid metabolism of *M. leprae*, an organism which upregulates several genes of the host´s lipid metabolism during infection [92]. The regulation of lipid droplet formation in the host cell is another important topic. Recent sudies revealed that intracellular pathogens induce the expression of LDL receptor and scavenger receptors CD36 and LOX1 for the internalization of native and oxidized fatty acids. Especially the generation of oxidized lipids by macrophage-derived reactive oxygen species seems to be an important mechanism for the induction of scavenger receptors.

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