Mycobacterium leprae, an obligate intracellular pathogen, shows a unique tropism for Schwann cells (SC). This leads to the peripheral neuropathy disorder observed in leprosy. In this study, we investigated signal transduction events and the intracellular fate of M. leprae during the interaction of the microorganism with SC. First, we demonstrated that the human schwannoma cell line ST88-14 readily phagocytized the bacteria as observed by time-lapse microscopy, actin staining and electron microscopy. The effect of specific kinase inhibitors on M. leprae internalization was then investigated showing that functional protein tyrosine kinase, calcium-dependent protein kinase and phosphatidylinositol 3-kinase, but not cAMP-dependent protein kinase are essential for phagocytosis of the bacteria. Similar results were obtained when irradiated and live bacteria were compared and when M. leprae was pre-coated with recombinant histone-like-protein/laminin binding protein, a bacterial adhesin. In addition, experiments were performed to analyze the bacterial trafficking within the endosomal network by labeling the acidified intracellular compartments of M. leprae-infected SC with the Lysotracker acidotrophic probe. Acidification of vesicles containing live M. leprae was minimal in both RAW murine macrophages and SC, although phagosomes containing heat-killed bacteria seem to follow normal endocytic maturation. These data indicate that the invading bacteria interfere with normal endocytic pathway maturation of bacteria-containing phagosomes within SC.
Bibliographical noteFunding Information:
The authors wish to thank James Krahenbuhl, Patrick Brennan and Janet Fitzakerly. This work was partially support by Grant ID A10325 from WHO/TDR and Papes 3 Grant from the Oswaldo Cruz Foundation. L. Alves was a recipient of a fellowship from CAPES (Brazil). We thank Mecia de Oliveira and Devki Nandan for critical reading of this manuscript and helpful discussions. Many thanks to Juliana P. Rodrigues, Vania W. A. Amaral and Tatiana P. Silva for their skilled technical assistance.
- Endocytic pathway
- Mycobacterium leprae
- Schwann cells