Leprosy is a chronic infectious disease caused by the intracellular pathogen Mycobacterium leprae. The disease may present different clinical forms depending on the immunological status of the host. M. leprae may infect macrophages and Schwann cells, and recent studies have demonstrated that macrophages are fundamental cells for determining the outcome of the disease. Skin lesions from patients with the paucibacillary form of the disease present a predominance of macrophages with a pro-inflammatory phenotype (M1), whereas skin lesions of multibacillary patients present a predominance of anti-inflammatory macrophages (M2). More recently, it was shown that autophagy is responsible for the control of bacillary load in paucibacillary macrophages and that the blockade of autophagy is involved in the onset of acute inflammatory reactional episodes in multibacillary cells. So, strategies that aim to induce autophagy in infected macrophages are promising not only to improve the efficacy of multidrug therapy (MDT) but also to avoid the occurrence of reactional episodes that are responsible for the disabilities observed in leprosy patients.2 production of nitric oxide, thus causing peripheral nerve damage characteristic of patients with leprosy [10]. Other studies have shown the ability of M. leprae to induce the production of oxidative mediators and their products, peroxynitrite and nitrotyrosine [11][12][13][14].Studies have demonstrated the ability of M. leprae to interact with a range of scavenger receptors of macrophages culminating in a tolerogenic response profile. The scavenger receptors are membrane receptors whose main function is the removal of molecules and cellular debris from the body, binding through a variety of polyanions, leading to phagocytosis of the target, being found in several cell types such as macrophages [15]. The ability of M. leprae to interact with the CD163 receptor, a scavenger receptor, which, during this interaction, can act as a co-receptor for M. leprae entry in macrophages, has been described [16]. It is known that activation of this receptor is related to the activation of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2), leading to the synthesis and increase of the activity of the enzyme heme oxygenase-1 (HO-1), which, through anti-inflammatory and antioxidant pathways, releases interleukin (IL)-10 and generates carbon monoxide, contributing to the polarization of these cells [17][18][19]. Bonilla and colleagues [20] demonstrated that autophagy, a mechanism of metabolic control, regulates the expression of scavenger receptors macrophage receptor with collagenous structure (MARCO) and scavenger receptor type A (SRA-I) that increase phagocytosis and NRF2 activity during Bacillus Calmette-Guérin (BCG) or M. tuberculosis (H37Rv) infection.M. leprae is able to induce macrophage SRA-I and CD36 expression [6] that contributes to the uptake of lipids, culminating in an increase in the uptake and accumulation of oxidized lipids within the macrophages, leading to a fo...

Leprosy reactional episodes are acute inflammatory events that may occur during the clinical course of the disease. Type 1 reaction (T1R) is associated with an increase in neural damage, and the understanding of the molecular pathways related to T1R onset is pivotal for the development of strategies that may effectively control the reaction. Interferon-gamma (IFN-γ) is a key cytokine associated with T1R onset and is also associated with autophagy induction. Here, we evaluated the modulation of the autophagy pathway in Mycobacterium leprae-stimulated cells in the presence or absence of IFN-γ. We observed that IFN-γ treatment promoted autophagy activation and increased the expression of genes related to the formation of phagosomes, autophagy regulation and function, or lysosomal pathways in M. leprae-stimulated cells. IFN-γ increased interleukin (IL)-15 secretion in M. leprae-stimulated THP-1 cells in a process associated with autophagy activation. We also observed higher IL15 gene expression in multibacillary (MB) patients who later developed T1R during clinical follow-up when compared to MB patients who did not develop the episode. By overlapping gene expression patterns, we observed 13 common elements shared between T1R skin lesion cells and THP-1 cells stimulated with both M. leprae and IFN-γ. Among these genes, the autophagy regulator Translocated Promoter Region, Nuclear Basket Protein (TPR) was significantly increased in T1R cells when compared with non-reactional MB cells. Overall, our results indicate that IFN-γ may induce a TPR-mediated autophagy transcriptional program in M. leprae-stimulated cells similar to that observed in skin cells during T1R by a pathway that involves IL-15 production, suggesting the involvement of this cytokine in the pathogenesis of T1R.

Pathogenic mycobacteria species may subvert the innate immune mechanisms and can modulate the activation of cells that cause disease in the skin. Cutaneous mycobacterial infection may present different clinical presentations and it is associated with stigma, deformity, and disability. The understanding of the immunopathogenic mechanisms related to mycobacterial infection in human skin is of pivotal importance to identify targets for new therapeutic strategies. The occurrence of reactional episodes and relapse in leprosy patients, the emergence of resistant mycobacteria strains, and the absence of effective drugs to treat mycobacterial cutaneous infection increased the interest in the development of therapies based on repurposed drugs against mycobacteria. The mechanism of action of many of these therapies evaluated is linked to the activation of autophagy. Autophagy is an evolutionary conserved lysosomal degradation pathway that has been associated with the control of the mycobacterial bacillary load. Here, we review the role of autophagy in the pathogenesis of cutaneous mycobacterial infection and discuss the perspectives of autophagy as a target for drug development and repurposing against cutaneous mycobacterial infection.

In HIV-infected individuals, a paradoxical clinical deterioration may occur in preexisting leprosy when highly active antiretroviral therapy (HAART)-associated reversal reaction (RR) develops. Leprosy-HIV co-infected patients during HAART may present a more severe form of the disease (RR/HIV), but the immune mechanisms related to the pathogenesis of leprosy-HIV co-infection remain unknown. Although the adaptive immune responses have been extensively studied in leprosy-HIV co-infected individuals, recent studies have described that innate immune cells may drive the overall immune responses to mycobacterial antigens. Monocytes are critical to the innate immune system and play an important role in several inflammatory conditions associated with chronic infections. In leprosy, different tissue macrophage phenotypes have been associated with the different clinical forms of the disease, but it is not clear how HIV infection modulates the phenotype of innate immune cells (monocytes or macrophages) during leprosy. In the present study, we investigated the phenotype of monocytes and macrophages in leprosy-HIV co-infected individuals, with or without RR. We did not observe differences between the monocyte profiles in the studied groups; however, analysis of gene expression within the skin lesion cells revealed that the RR/HIV group presents a higher expression of macrophage scavenger receptor 1 (MRS1), CD209 molecule (CD209), vascular endothelial growth factor (VEGF), arginase 2 (ARG2), and peroxisome proliferator-activated receptor gamma (PPARG) when compared with the RR group. Our data suggest that different phenotypes of tissue macrophages found in the skin from RR and RR/HIV patients could differentially contribute to the progression of leprosy.