The Differential In Vitro Presentation of Mycobacterium leprae Antigens by Human Dendritic Cells is determined by the Mechanism of Host Cell Adhesion.

Clinical manifestations in leprosy, a chronic infectious disease caused by Mycobacterium leprae, depend on the immunologic reactions of the patient to the bacilli. Previously, we have shown a reversion of the inefficiency of the cellular-mediated immune response against M. leprae in lepromatous leprosy patients when dendritic cells (DCs) were used in vitro as APC. The aim of the current study is to investigate the cell-to-cell interaction when purified human monocytes-derived DCs and macrophages from healthy adult donors were co-cultured with autologous lymphocytes in the presence of either M. leprae or M. bovis BCG by using APCs which were either attached or in suspension. Subsequently, APCs were analyzed by optical microscopy, phenotypically monitored by flow cytometry, and cytokines secretion evaluated by ELISA and Luminex. Overall, our results suggest that: (1) the process of adhesion of the APC may not be absolutely essential for antigen presentation activity; (2) IL-12 production appears to be in direct relation to the susceptibility of the host cell to infection with M. leprae; (3) in the presence of autologous lymphocytes, there is a down-modulation of surface markers studied, except for CD209 in M. leprae-infected CD11c+ DCs, although a similar decreased expression of these markers on macrophages was also observed, and this step occurs in an antigen-dependent manner; and (4) the cytokines secretion is also dependent on the APCs’ adhesion process. In parallel, the human THP-1 cell line was assessed showing that no monokine was differentially regulated when cells remained either attached or in suspension, regardless of the stimulus employed. These results may further guide future pivotal experimental procedures when studying in vitro cellular immune responses against mycobacteria.