[Mycobacterium leprae: behavior in the adipocyte undergoing differentiation]

We have investigated the behaviour of M. leprae in murine preadipocyte cells (clone Ob17) undergoing the adipose cell conversion process in vitro. Actively differentiating Ob17 cells were infected with M. leprae. The morphological index (MI) of the acid-fast bacteria (AFB) present at day 12 and day 25 after infection was compared to the MI of the AFB inoculated. An increase of the MI was consistently observed. This increase is suppressed by rifampicin. Due to important cell loss, an increase of the number of the AFB per culture could not be obtained in monolayer tissue cultures. In order to prevent cell loss, we used a three-dimensional culture system. This cell culture system is an in vitro reconstitution of the human dermis, a main target organ for the leprosy bacillus. Adipocytes infected with M. leprae are incorporated in a condensed collagen lattice together with skin fibroblasts. Under such conditions, both an increase of the MI and an increase of the number of the AFB are obtained. This suggests that cellular functions related to the adipose cell differentiation process might complement the defective bacterial genome, leading to transient multiplication in vitro.