CYBB-Mediated Ferroptosis Associated with Immunosuppression in Mycobacterium leprae-Infected Monocyte-Derived Macrophages.

Mycobacterium leprae-infected macrophages preferentially exhibit the regulatory M2 phenotype in vitro, which helps the immune escape unabated growth of M leprae in host cells. The mechanism that triggers macrophage polarization is still unknown. In this study, we performed single-cell RNA sequencing to determine the initial responses of human monocyte-derived macrophages against M leprae infection of 4 healthy individuals and found an increase in a major alternative-activated macrophage type that overexpressed NEAT1, CCL2, and CD163. Importantly, further functional analysis showed that ferroptosis was positively correlated with M2 polarization of macrophages, and in vitro experiments have shown that inhibition of ferroptosis promotes the survival of M leprae within macrophages. In addition, further joint analysis of our results with mutisequencing data from patients with leprosy and in vitro validation identified that CYBB was the pivotal molecule for ferroptosis that could promote the M2 polarization of M leprae-infected macrophages, resulting in the immune escape and unabated growth of pathogenic bacteria. Overall, our results suggest that M leprae facilitated its survival by inducing CYBB-mediated macrophage ferroptosis leading to its alternative activation and might reveal the potential for a new therapeutic strategy of leprosy.

Single-cell sequencing analysis reveals development and differentiation trajectory of Schwann cells manipulated by M. leprae.

BACKGROUND: M. leprae preferentially infects Schwann cells (SCs) in the peripheral nerves leading to nerve damage and irreversible disability. Knowledge of how M. leprae infects and interacts with host SCs is essential for understanding mechanisms of nerve damage and revealing potential new therapeutic strategies. METHODOLOGY/PRINCIPAL FINDINGS: We performed a time-course single-cell sequencing analysis of SCs infected with M. leprae at different time points, further analyzed the heterogeneity of SCs, subpopulations associated with M. leprae infection, developmental trajectory of SCs and validated by Western blot or flow cytometry. Different subpopulations of SCs exhibiting distinct genetic features and functional enrichments were present. We observed two subpopulations associated with M. leprae infection, a stem cell-like cell subpopulation increased significantly at 24 h but declined by 72 h after M. leprae infection, and an adipocyte-like cell subpopulation, emerged at 72 h post-infection. The results were validated and confirmed that a stem cell-like cell subpopulation was in the early stage of differentiation and could differentiate into an adipocyte-like cell subpopulation. CONCLUSIONS/SIGNIFICANCE: Our results present a systematic time-course analysis of SC heterogeneity after infection by M. leprae at single-cell resolution, provide valuable information to understand the critical biological processes underlying reprogramming and lipid metabolism during M. leprae infection of SCs, and increase understanding of the disease-causing mechanisms at play in leprosy patients as well as revealing potential new therapeutic strategies.

IL-23/IL-23R Promote Macrophage Pyroptosis and T Helper 1/T Helper 17 Cell Differentiation in Mycobacterial Infection.

Pathogen-induced epigenetic modifications can reshape anti-infection immune processes and control the magnitude of host responses. DNA methylation profiling has identified crucial aberrant methylation changes associated with diseases, thus providing biological insights into the roles of epigenetic factors in mycobacterial infection. In this study, we performed a genome-wide methylation analysis of skin biopsies from patients with leprosy and healthy controls. T helper 17 differentiation pathway was found to be significantly associated with leprosy through functional enrichment analysis. As a key gene in this pathway, IL-23R was found to be critical to mycobacterial immunity in leprosy, according to integrated analysis with DNA methylation, RNA sequencing, and GWASs. Functional analysis revealed that IL-23/IL-23R-enhanced bacterial clearance by activating caspase-1/GSDMD-mediated pyroptosis in a manner dependent on NLRP3 through signal transducer and activator of transcription 3 signaling in macrophages. Moreover, IL23/IL-23R promoted T helper 1 and T helper 17 cell differentiation and proinflammatory cytokine secretion, thereby increasing host bactericidal activity. IL-23R knockout attenuated the effects and increased susceptibility to mycobacterial infection mentioned earlier. These findings illustrate the biological functions of IL-23/IL-23R in modulating intracellular bacterial clearance in macrophages and further support their regulatory effects in T helper cell differentiation. Our study highlights that IL-23/IL-23R might serve as potential targets for the prevention and treatment of leprosy and other mycobacterial infections.

Case Report: Lepromatous Leprosy and Psoriasis: An Uncommon Coincidence.

Leprosy, a chronic infectious disease, and psoriasis, an inflammatory disorder, are distinct entities. Epidemiology data show that these two diseases are almost mutually exclusive, with only a few reported cases of their coexistence. Here, we present the case of a patient manifesting intermingled psoriatic and leprosy lesions diagnosed as borderline lepromatous leprosy and plaque psoriasis. Of note, Mycobacterium leprae bacilli were detected not only in the two types of lesions but also in normal-appearing skin and blood.

The immune-suppressive landscape in lepromatous leprosy revealed by single-cell RNA sequencing.

Lepromatous leprosy (L-LEP), caused by the massive proliferation of Mycobacterium leprae primarily in macrophages, is an ideal disease model for investigating the molecular mechanism of intracellular bacteria evading or modulating host immune response. Here, we performed single-cell RNA sequencing of both skin biopsies and peripheral blood mononuclear cells (PBMCs) of L-LEP patients and healthy controls. In L-LEP lesions, we revealed remarkable upregulation of APOE expression that showed a negative correlation with the major histocompatibility complex II gene HLA-DQB2 and MIF, which encodes a pro-inflammatory and anti-microbial cytokine, in the subset of macrophages exhibiting a high expression level of LIPA. The exhaustion of CD8+ T cells featured by the high expression of TIGIT and LAG3 in L-LEP lesions was demonstrated. Moreover, remarkable enhancement of inhibitory immune receptors mediated crosstalk between skin immune cells was observed in L-LEP lesions. For PBMCs, a high expression level of APOE in the HLA-DRhighFBP1high monocyte subset and the expansion of regulatory T cells were found to be associated with L-LEP. These findings revealed the primary suppressive landscape in the L-LEP patients, providing potential targets for the intervention of intracellular bacteria caused persistent infections.