Cholesterol dynamics in macrophages implication for the bacteriology and pathology of leprosy.

M. leprae in the host multiplies abundantly in macrophages rich in cholesterol. Host-grown leprosy bacilli have an extremely high cholesterol content and in this respect they occupy a unique place among procariotic cells. M. leprae takes up cholesterol from the environment and it is not clear whether it can synthesize cholesterol and if so from which precursors. Mycobacteria can be grown from leprous tissues in primary cultures only in the presence of cholesterol. These strains quickly adapt to in vitro substrates and are able to synthesize cholesterol from still-unknown chemical entities, which are also sources of carbon and energy. These still unknown substrates will probably have to be discovered before cultivation of these elusive microorganisms is achieved and we approach a better understanding of the chemical mediators in the cellular defence and/or pathology of leprosy.