Autophagy-Associated IL-15 Production Is Involved in the Pathogenesis of Leprosy Type 1 Reaction.

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.

Innate Immune Responses in Leprosy.

Leprosy is an infectious disease that may present different clinical forms depending on host immune response to Mycobacterium leprae. Several studies have clarified the role of various T cell populations in leprosy; however, recent evidences suggest that local innate immune mechanisms are key determinants in driving the disease to its different clinical manifestations. Leprosy is an ideal model to study the immunoregulatory role of innate immune molecules and its interaction with nervous system, which can affect homeostasis and contribute to the development of inflammatory episodes during the course of the disease. Macrophages, dendritic cells, neutrophils, and keratinocytes are the major cell populations studied and the comprehension of the complex networking created by cytokine release, lipid and iron metabolism, as well as antimicrobial effector pathways might provide data that will help in the development of new strategies for leprosy management.

Elevated Pentraxin-3 Concentrations in Patients With Leprosy: Potential Biomarker of Erythema Nodosum Leprosum.

Background: Leprosy, the leading infectious cause of disability worldwide, remains a major public health challenge in the most severely affected countries despite the sharp decline in new cases in recent years. The search for biomarkers is essential to achieve a better understanding of the molecular and cellular mechanisms underlying the disease. Methods: Pentraxin-3 (PTX3) analyses of sera from 87 leprosy patients with or without reactions were conducted via enzyme-linked immunosorbent assay. In situ identification of PTX3 in skin lesion was confirmed by quantitative reverse-transcription polymerase chain reaction, immunohistochemistry, and immunofluorescence assays. Results: We found that PTX3 serum levels were higher in multibacillary patients when evaluated before the onset of acute erythema nodosum leprosum (ENL) and persistently elevated during reaction. Thalidomide treatment reduced PTX3 in the serum 7 days after starting treatment. In situ analyses have also demonstrated enhancement of PTX3 in ENL lesions and showed that treatment with thalidomide reduced its expression and the prominent neutrophilic infiltrate, a hallmark of the disease. Conclusions: In summary, our study provides in vivo evidence that PTX3 is enhanced during ENL but not in reversal reaction and provides a new molecular target in ENL pathogenesis.

Autophagy Is an Innate Mechanism Associated with Leprosy Polarization.

Leprosy is a chronic infectious disease that may present different clinical forms according to the immune response of the host. Levels of IFN-γ are significantly raised in paucibacillary tuberculoid (T-lep) when compared with multibacillary lepromatous (L-lep) patients. IFN-γ primes macrophages for inflammatory activation and induces the autophagy antimicrobial mechanism. The involvement of autophagy in the immune response against Mycobacterium leprae remains unexplored. Here, we demonstrated by different autophagic assays that LC3-positive autophagosomes were predominantly observed in T-lep when compared with L-lep lesions and skin-derived macrophages. Accumulation of the autophagic receptors SQSTM1/p62 and NBR1, expression of lysosomal antimicrobial peptides and colocalization analysis of autolysosomes revealed an impairment of the autophagic flux in L-lep cells, which was restored by IFN-γ or rapamycin treatment. Autophagy PCR array gene-expression analysis revealed a significantly upregulation of autophagy genes (BECN1, GPSM3, ATG14, APOL1, and TPR) in T-lep cells. Furthermore, an upregulation of autophagy genes (TPR, GFI1B and GNAI3) as well as LC3 levels was observed in cells of L-lep patients that developed type 1 reaction (T1R) episodes, an acute inflammatory condition associated with increased IFN-γ levels. Finally, we observed increased BCL2 expression in L-lep cells that could be responsible for the blockage of BECN1-mediated autophagy. In addition, in vitro studies demonstrated that dead, but not live M. leprae can induce autophagy in primary and lineage human monocytes, and that live mycobacteria can reduce the autophagy activation triggered by dead mycobacteria, suggesting that M. leprae may hamper the autophagic machinery as an immune escape mechanism. Together, these results indicate that autophagy is an important innate mechanism associated with the M. leprae control in skin macrophages.

STING-Dependent 2'-5' Oligoadenylate Synthetase-Like Production Is Required for Intracellular Mycobacterium leprae Survival.

Cytosolic detection of nucleic acids elicits a type I interferon (IFN) response and plays a critical role in host defense against intracellular pathogens. Herein, a global gene expression profile of Mycobacterium leprae-infected primary human Schwann cells identified the genes differentially expressed in the type I IFN pathway. Among them, the gene encoding 2'-5' oligoadenylate synthetase-like (OASL) underwent the greatest upregulation and was also shown to be upregulated in M. leprae-infected human macrophage cell lineages, primary monocytes, and skin lesion specimens from patients with a disseminated form of leprosy. OASL knock down was associated with decreased viability of M. leprae that was concomitant with upregulation of either antimicrobial peptide expression or autophagy levels. Downregulation of MCP-1/CCL2 release was also observed during OASL knock down. M. leprae-mediated OASL expression was dependent on cytosolic DNA sensing mediated by stimulator of IFN genes signaling. The addition of M. leprae DNA enhanced nonpathogenic Mycobacterium bovis bacillus Calmette-Guerin intracellular survival, downregulated antimicrobial peptide expression, and increased MCP-1/CCL2 secretion. Thus, our data uncover a promycobacterial role for OASL during M. leprae infection that directs the host immune response toward a niche that permits survival of the pathogen.