Mycobacterium bovis BCG but not Mycobacterium leprae Induces TNF-a Secretion in Human Monocytic THP-1 Cells

In this study, we compared the level of TNF-α secretion induced in monocytic THP-1 cells after phagocytosis of Mycobacterium leprae   , the causative agent of leprosy, and M. bovis BCG, an attenuated strain used as a vaccine against leprosy and tuberculosis. The presence of M. leprae and BCG was observed in more than 80% of the cells after 24 h of exposure. However, BCG but not M. leprae was able to induce TNF-α secretion in these cells. Moreover, THP-1 cells treated simultaneously with BCG and M. leprae secreted lower levels of TNF-α compared to cells incubated with BCG alone. M. leprae was able, however, to induce TNF-α secretion both in blood-derived monocytes as well as in THP-1 cells pretreated with phorbol myristate acetate. The inclusion of streptomycin in our cultures, together with the fact that the use of both gamma-irradiated M. leprae and heat-killed BCG gave similar results, indicate that the differences observed were not due to differences in viability but in intrinsic properties between M. leprae and BCG. These data suggest that the capacity of M. leprae to induce TNF-α is dependent on the stage of cell maturation and emphasize the potential of this model to explore differences in the effects triggered by vaccine strain versus pathogenic species of mycobacteria on the host cell physiology and metabolism

Efficient uptake of mannosylated proteins by a human Schwann cell line

Complex carbohydrate structures are essential molecules of infectious microbes and host cells, and are involved in cell signaling associated with inflammatory and immune responses. The uptake of mannose-tailed glycans is usually carried out by macrophages, dendritic cells (DCs), and other professional phagocytes to trigger MHC class I- and MHC class II-restricted antigen presentation, and to promote T cell effector responses. Since Schwann cells (SCs) have been proposed as immunocompetent cells, we investigated whether a human cell line (ST88-14 cells) could bind mannosylated ligands in a specific manner. The saturation of uptake of mannosylated molecules by ST88-14 cells and the internalization and distribution pathway of these ligands were tested by cytometry and confocal plus electron microscopy, respectively. This uptake showed a dose-dependent increase, the saturation point being reached at high concentrations of mannosyl residues/240mM mannose. Merging of man/BSA-FITC and S100 labeling showed their partial, but, significant colocalization. Ultrastructural analysis of ST88-14 cells after incubation with HRP-colloidal gold, without or with subsequent chasing at 37°C, showed an initial location on the cell surface and temperature- and time-dependent internalization of the probe. Our findings suggest an efficient mannosylated ligand uptake system through putative lectin(s) that may be operational in inflammatory and immune responses

Mycobacterium leprae downregulates the expression of PHEX in Schwann cells and osteoblasts

Neuropathy and bone deformities, lifelong sequelae of leprosy that persist after treatment, result in significant impairment to patients and compromise their social rehabilitation. Phosphate-regulating gene with homologies to endopeptidase on the X chromosome (PHEX) is a Zn-metalloendopeptidase, which is abundantly expressed in osteoblasts and many other cell types, such as Schwann cells, and has been implicated in phosphate metabolism and X-linked rickets. Here, we demonstrate that Mycobacterium leprae stimulation downregulates PHEX transcription and protein expression in a human schwannoma cell line (ST88-14) and human osteoblast lineage. Modulation of PHEX expression was observed to a lesser extent in cells stimulated with other species of mycobacteria, but was not observed in cultures treated with latex beads or with the facultative intracellular bacterium Salmonella typhimurium. Direct downregulation of PHEX by M. leprae could be involved in the bone resorption observed in leprosy patients. This is the first report to describe PHEX modulation by an infectious agent