Differential immunoglobulin and complement levels in leprosy prior to development of reversal reaction and erythema nodosum leprosum

Probing Dermal Immunity to Mycobacteria through a Controlled Human Infection Model

Cutaneous mycobacterial infections cause substantial morbidity and are challenging to diagnose and treat. An improved understanding of the dermal immune response to mycobacteria may inspire new therapeutic approaches. We conducted a controlled human infection study with 10 participants who received 2 × 106 CFUs of Mycobacterium bovis bacillus Calmette-Guérin (Tice strain) intradermally and were randomized to receive isoniazid or no treatment. Peripheral blood was collected at multiple time points for flow cytometry, bulk RNA sequencing (RNA-seq), and serum Ab assessments. Systemic immune responses were detected as early as 8 d postchallenge in this M. bovis bacillus Calmette-Guérin-naive population. Injection-site skin biopsies were performed at days 3 and 15 postchallenge and underwent immune profiling using mass cytometry and single-cell RNA-seq, as well as quantitative assessments of bacterial viability and burden. Molecular viability testing and standard culture results correlated well, although no differences were observed between treatment arms. Single-cell RNA-seq revealed various immune and nonimmune cell types in the skin, and communication between them was inferred by ligand-receptor gene expression. Day 3 communication was predominantly directed toward monocytes from keratinocyte, muscle, epithelial, and endothelial cells, largely via the migration inhibitory factor pathway and HLA-E-KLRK1 interaction. At day 15, communication was more balanced between cell types. These data reveal the potential role of nonimmune cells in the dermal immune response to mycobacteria and the utility of human challenge studies to augment our understanding of mycobacterial infections.

IgG seroprevalence of Toxoplasma gondii and Leishmania infantum in leprosy patients: Implications for screening and management of co-infections

Parasitic co-infections are common in developing countries and can interfere with leprosy treatment, leading to an increased risk of inflammatory leprosy reactions. This study assessed serum immunoglobulin G (IgG) levels against Toxoplasma gondii and Visceral Leishmaniasis (VL) antigens in 270 leprosy patients from Brazilian states. Regarding the respective cut-offs, the prevalence of IgG seropositivity for T. gondii and VL were 21.05 % and 47.36 % in the leprosy-negative group, and 77.7 % and 52.6 % in the leprosy-positive group. Of the 270 leprosy patients, 158 (58.5 %) presented with inflammatory leprosy reactions. Of those, 72 (59.5 %) had neuritis, 35 (48.6 %) had reverse reactions, and 28 (38.9 %) had ENL in both Brazilian states. Leprosy patients with anti-Leishmania IgG seropositivity were 3.25 times more likely to develop neuritis (95 % C.I.: 1.187 - 9.154; p = 0.019). These findings are particularly relevant for clinical settings where both leprosy and parasitic diseases are prevalent and could provide essential guidance for detecting and addressing complications arising from parasitic co-infections in leprosy patients, thereby improving clinical management strategies.

Sequential trypsin and ProAlanase digestions unearth immunological protein biomarkers shrouded by skeletal collagen

This study investigates the efficacy of proteomic analysis of human remains to identify active infections in the past through the detection of pathogens and the host response to infection. We advance leprosy as a case study due to the sequestering of sufferers in leprosaria and the suggestive skeletal lesions that can result from the disease. Here we present a sequential enzyme extraction protocol, using trypsin followed by ProAlanase, to reduce the abundance of collagen peptides and in so doing increase the detection of non-collagenous proteins. Through our study of five individuals from an 11th to 18th century leprosarium, as well as four from a contemporaneous non-leprosy associated cemetery in Barcelona, we show that samples from 2 out of 5 leprosarium individuals extracted with the sequential digestion methodology contain numerous host immune proteins associated with modern leprosy. In contrast, individuals from the non-leprosy associated cemetery and all samples extracted with a trypsin-only protocol did not. Through this study, we advance a palaeoproteomic methodology to gain insights into the health of archaeological individuals and take a step toward a proteomics-based method to study immune responses in past populations.

Immunopathogenesis of Type 1 and Type 2 Leprosy Reaction: An Update Review

Leprosy reactions are acute exacerbations of the signs and symptoms of leprosy occurring during the natural course of the disease and during or after treatment. Left untreated or improperly managed, reactions can lead to severe nerve function impairment and subsequently to disabilities. In the present context of leprosy eradication efforts, leprosy reactions continue to pose a significant and enduring challenge. Type 1 leprosy reaction and type 2 leprosy reaction are substantial contributors to nerve impairment and the subsequent development of enduring impairments. The study of immunopathogenesis of leprosy reactions has emerged as a significant area of research due to its potential to identify critical targets for the early detection and management of these episodes. This study aims to reveal the pathogenesis of type 1 and 2 leprosy reactions so that they can form the basis for their treatment. The study used scientific journals from reputable platforms such as PubMed, Scopus, and Google Scholar to evaluate the pathogenesis of leprosy reaction type 1 and 2 in leprosy patients. This review indicates that the progression of leprosy nerve damage and sensitivity to reactions may be predicted using genetic and serum markers in the human host. A more profound comprehension of the molecular processes underlying leprosy reactions may offer a logical plan for early detection and leprosy reaction complication prevention.

Pathogenicity and virulence of Mycobacterium leprae

Leprosy is caused by Mycobacterium leprae (M. leprae) and M. lepromatosis, an obligate intracellular organism, and over 200,000 new cases occur every year. M. leprae parasitizes histiocytes (skin macrophages) and Schwann cells in the peripheral nerves. Although leprosy can be treated by multidrug therapy, some patients relapse or have a prolonged clinical course and/or experience leprosy reaction. These varying outcomes depend on host factors such as immune responses against bacterial components that determine a range of symptoms. To understand these host responses, knowledge of the mechanisms by which M. leprae parasitizes host cells is important. This article describes the characteristics of leprosy through bacteriology, genetics, epidemiology, immunology, animal models, routes of infection, and clinical findings. It also discusses recent diagnostic methods, treatment, and measures according to the World Health Organization (WHO), including prevention. Recently, the antibacterial activities of anti-hyperlipidaemia agents against other pathogens, such as M. tuberculosis and Staphylococcus aureus have been investigated. Our laboratory has been focused on the metabolism of lipids which constitute the cell wall of M. leprae. Our findings may be useful for the development of future treatments.

Host-Related Laboratory Parameters for Leprosy Reactions

Leprosy reactions are acute inflammatory episodes that complicate the course of a Mycobacterium leprae infection and are the major cause of leprosy-associated pathology. Two types of leprosy reactions with relatively distinct pathogenesis and clinical features can occur: type 1 reaction, also known as reversal reaction, and type 2 reaction, also known as erythema nodosum leprosum. These acute nerve-destructive immune exacerbations often cause irreversible disabilities and deformities, especially when diagnosis is delayed. However, there is no diagnostic test to detect or predict leprosy reactions before the onset of clinical symptoms. Identification of biomarkers for leprosy reactions, which impede the development of symptoms or correlate with early-onset, will allow precise diagnosis and timely interventions to greatly improve the patients' quality of life. Here, we review the progress of research aimed at identifying biomarkers for leprosy reactions, including its correlation with not only immunity but also genetics, transcripts, and metabolites, providing an understanding of the immune dysfunction and inflammation that underly the pathogenesis of leprosy reactions. Nevertheless, no biomarkers that can reliably predict the subsequent occurrence of leprosy reactions from non-reactional patients and distinguish type I reaction from type II have yet been found.

Image Morphometric Analysis of B Cells and Plasma Cells in Erythema Nodosum Leprosum With Clinicopathological Correlation

ABSTRACT

Erythema nodosum leprosum (ENL) occurs as an immunological complication of multibacillary leprosy (MBL). The pathogenesis of ENL is long considered to be a T-cell-mediated process. The role of B cells and plasma cells in ENL is not well described in the literature. Therefore, we investigated the B-cell and plasma cell infiltrates in the skin biopsies of biopsy-proven cases of ENL by immunohistochemistry and image morphometry and compared the result with paucibacillary leprosy and MBL. Moreover, we sought a correlation of the B-cell and plasma cell infiltrates with different clinical, hematological, histopathological, and bacteriological parameters as well as the T-cell subsets in the skin biopsies. Our study highlighted a significant reduction in the number of B cells from paucibacillary leprosy to MBL to ENL, although there was no significant variation in the plasma cell infiltrate. The plasma cell infiltrate correlated with absolute neutrophilia in the blood and the presence of eosinophils in the ENL lesions. Both B cells and plasma cells positively correlated with CD4-positive T-helper cells and the CD8-positive cytotoxic T cells. Besides, the B cells also correlated positively with the CD3-positive pan T cells in the biopsy and negatively correlated with the T-regulatory:T-cell ratio. Our results suggested the role of B cells and plasma cells even at the tissue level in the pathobiogenesis of ENL.

Changes in B Cell Pool of Patients With Multibacillary Leprosy: Diminished Memory B Cell and Enhanced Mature B in Peripheral Blood

Despite being treatable, leprosy still represents a major public health problem, and many mechanisms that drive leprosy immunopathogenesis still need to be elucidated. B cells play important roles in immune defense, being classified in different subgroups that present distinct roles in the immune response. Here, the profile of B cell subpopulations in peripheral blood of patients with paucibacillary (TT/BT), multibacillary (LL/BL) and erythema nodosum leprosum was analyzed. B cell subpopulations (memory, transition, plasmablasts, and mature B cells) and levels of IgG were analyzed by flow cytometry and ELISA, respectively. It was observed that Mycobacterium leprae infection can alter the proportions of B cell subpopulations (increase of mature and decrease of memory B cells) in patients affected by leprosy. This modulation is associated with an increase in total IgG and the patient's clinical condition. Circulating B cells may be acting in the modulation of the immune response in patients with various forms of leprosy, which may reflect the patient's ability to respond to M. leprae.

Serum IgA Antibodies Specific to M. leprae Antigens as Biomarkers for Leprosy Detection and Household Contact Tracking

Leprosy remains endemic in several developing countries, such as India and Brazil, in part due to delayed diagnosis that facilitates ongoing transmission. Although immunoglobulins against several Mycobacterium leprae antigens have been indicated for the early diagnosis, and IgA participates in the early stages of leprosy and in subclinical infection, relatively little research has examined anti-M. leprae IgA responses. Here, we investigated serum IgA reactivity against NDO-HSA, LID-1 and NDO-LID, in paucibacillary (PB) and multibacillary (MB) patients and their household contacts, using enzyme-linked immunosorbent assay (ELISA). Diagnostic accuracy of each ELISA was evaluated by receiver operating characteristic (ROC) curve analysis. Our data reveal elevated IgA serum levels against the three M. leprae specific antigens in MB patients, whereas IgA reactivity in PB patients was increased only to NDO-HSA. Further, MB and PB household contacts displayed higher IgA reactivity to NDO-HSA than non-endemic controls. Our data suggest measurement of serum IgA against NDO-HSA as an additional tool in the diagnosis and classification of the disease, with potential utility for household contact follow-up.

Neutrophil NETworking in ENL: Potential as a Putative Biomarker: Future Insights

Erythema nodosum leprosum (ENL), also known as type 2 reaction (T2R) is an immune complex mediated (type III hypersensitivity) reactional state encountered in patients with borderline lepromatous and lepromatous leprosy (BL and LL) either before, during, or after the institution of anti-leprosy treatment (ALT). The consequences of ENL may be serious, leading to permanent nerve damage and deformities, constituting a major cause of leprosy-related morbidity. The incidence of ENL is increasing with the increasing number of multibacillary cases. Although the diagnosis of ENL is not difficult to make for physicians involved in the care of leprosy patients, its management continues to be a most challenging aspect of the leprosy eradication program: the chronic and recurrent painful skin lesions, neuritis, and organ involvement necessitates prolonged treatment with prednisolone, thalidomide, and anti-inflammatory and immunosuppressive drugs, which further adds to the existing morbidity. In addition, the use of immunosuppressants like methotrexate, azathioprine, cyclosporine, or biologics carries a risk of reactivation of persisters (Mycobacterium leprae), apart from their own end-organ toxicities. Most ENL therapeutic guidelines are primarily designed for acute episodes and there is scarcity of literature on management of patients with chronic and recurrent ENL. It is difficult to predict which patients will develop chronic or recurrent ENL and plan the treatment accordingly. We need simple point-of-care or ELISA-based tests from blood or skin biopsy samples, which can help us in identifying patients who are likely to require prolonged treatment and also inform us about the prognosis of reactions so that appropriate therapy may be started and continued for better ENL control in such patients. There is a significant unmet need for research for better understanding the immunopathogenesis of, and biomarkers for, ENL to improve clinical stratification and therapeutics. In this review we will discuss the potential of neutrophils (polymorphonuclear granulocytes) as putative diagnostic and prognostic biomarkers by virtue of their universal abundance in human blood, functional versatility, phenotypic heterogeneity, metabolic plasticity, differential hierarchical cytoplasmic granule mobilization, and their ability to form NETs (neutrophil extracellular traps). We will touch upon the various aspects of neutrophil biology relevant to ENL pathophysiology in a step-wise manner. We also hypothesize about an element of metabolic reprogramming of neutrophils by M. leprae that could be investigated and exploited for biomarker discovery. In the end, a potential role for neutrophil derived exosomes as a novel biomarker for ENL will also be explored.

Susceptibility and resistance in leprosy: Studies in the mouse model

Leprosy is a chronic granulomatous infectious disease caused by the pathogen, Mycobacterium leprae, and the more recently discovered, M. lepromatosis. Described in 1873, M. leprae was among the first microorganisms to be proposed as a cause of a human infectious disease. As an obligate intracellular bacterium, it has still not thus far been reproducibly cultivated in axenic medium or cell cultures. Shepard's mouse footpad assay, therefore, was truly a breakthrough in leprosy research. The generation of immunosuppressed and genetically engineered mice, along with advances in molecular and cellular techniques, has since offered more tools for the study of the M. leprae–induced granuloma. While far from perfect, these new mouse models have provided insights into the immunoregulatory mechanisms responsible for the spectrum of this complex disease.

The Role of Complement System and the Immune Response to Tuberculosis Infection

The complement system orchestrates a multi-faceted immune response to the invading pathogen, Mycobacterium tuberculosis. Macrophages engulf the mycobacterial bacilli through bacterial cell surface proteins or secrete proteins, which activate the complement pathway. The classical pathway is activated by C1q, which binds to antibody antigen complexes. While the alternative pathway is constitutively active and regulated by properdin, the direct interaction of properdin is capable of complement activation. The lectin-binding pathway is activated in response to bacterial cell surface carbohydrates such as mannose, fucose, and N-acetyl-d-glucosamine. All three pathways contribute to mounting an immune response for the clearance of mycobacteria. However, the bacilli can reside, persist, and evade clearance by the immune system once inside the macrophages using a number of mechanisms. The immune system can compartmentalise the infection into a granulomatous structure, which contains heterogenous sub-populations of M. tuberculosis. The granuloma consists of many types of immune cells, which aim to clear and contain the infection whilst sacrificing the affected host tissue. The full extent of the involvement of the complement system during infection with M. tuberculosis is not fully understood. Therefore, we reviewed the available literature on M. tuberculosis and other mycobacterial literature to understand the contribution of the complement system during infection.

Adding MASP1 to the lectin pathway-Leprosy association puzzle: Hints from gene polymorphisms and protein levels

BACKGROUND

Deposition of complement factors on Mycobacterium leprae may enhance phagocytosis. Such deposition may occur through the lectin pathway of complement. Three proteins of the lectin pathway are produced from the gene MASP1: Mannan-binding lectin-associated serine protease 1 (MASP-1) and MASP-3 and mannan-binding lectin-associated protein of 44 kDa (MAp44). Despite their obvious importance, the roles played by these proteins have never been investigated in leprosy disease.

METHODOLOGY

We haplotyped five MASP1 polymorphisms by multiplex sequence-specific PCR (intronic rs7609662*G>A and rs13064994*C>T, exon 12 3'-untranslated rs72549262*C>G, rs1109452*C>T and rs850314*G>A) and measured MASP-1, MASP-3 and MAp44 serum levels in 196 leprosy patients (60%, lepromatous) and 193 controls.

PRINCIPAL FINDINGS

Lower MASP-3 and MAp44 levels were observed in patients, compared with controls (P = 0.0002 and P<0.0001, respectively) and in lepromatous, compared with non-lepromatous patients (P = 0.008 and P = 0.002, respectively). Higher MASP-3 levels were present in controls carrying variants/haplotypes associated with leprosy resistance (rs13064994*T, rs1109452_rs850314*CG within GT_CCG and rs850314*A: OR = 0.5-0.6, Pcorr = 0.01-0.04). Controls with rs1109452*T, included in susceptibility haplotypes (GT_GTG/GT_CTG: OR = 2.0, Pcorr = 0.03), had higher MASP-1 and lower MASP-3 levels (P≤0.009). Those with GC_CCG, presented increasing susceptibility (OR = 1.7, Pcorr = 0.006) and higher MAp44 levels (P = 0.015). MASP-3 expression decreased in patients, compared with controls carrying rs1109452_rs850314*CA or CG (P≤0.02), which may rely on exon 12 CpG methylation and/or miR-2861/miR-3181 mRNA binding.

CONCLUSION

Polymorphisms regulating MASP-3/MAp44 availability in serum modulate leprosy susceptibility, underlining the importance of lectin pathway regulation against pathogens that exploit phagocytosis to parasitize host macrophages.

The Many Hosts of Mycobacteria 8 (MHM8): A conference report

Mycobacteria are important causes of disease in human and animal hosts. Diseases caused by mycobacteria include leprosy, tuberculosis (TB), nontuberculous mycobacteria (NTM) infections and Buruli Ulcer. To better understand and treat mycobacterial disease, clinicians, veterinarians and scientists use a range of discipline-specific approaches to conduct basic and applied research, including conducting epidemiological surveys, patient studies, wildlife sampling, animal models, genetic studies and computational simulations. To foster the exchange of knowledge and collaboration across disciplines, the Many Hosts of Mycobacteria (MHM) conference series brings together clinical, veterinary and basic scientists who are dedicated to advancing mycobacterial disease research. Started in 2007, the MHM series recently held its 8th conference at the Albert Einstein College of Medicine (Bronx, NY). Here, we review the diseases discussed at MHM8 and summarize the presentations on research advances in leprosy, NTM and Buruli Ulcer, human and animal TB, mycobacterial disease comorbidities, mycobacterial genetics and 'omics, and animal models. A mouse models workshop, which was held immediately after MHM8, is also summarized. In addition to being a resource for those who were unable to attend MHM8, we anticipate this review will provide a benchmark to gauge the progress of future research concerning mycobacteria and their many hosts.

Utility and limitations of serodiagnostic tests in monitoring the response to treatment of leprosy patients

Simple measures that can facilitate early recognition of leprosy complications are still lacking. We therefore evaluated a lateral flow-based rapid diagnostic test and fast enzyme-linked immunosorbent assay measuring anti-LID-NDO antibody responses among leprosy cases in Cebu, Philippines. Responses were measured at diagnosis, then during and after the provision of standard multidrug therapy. Our data indicate that both platforms are highly sensitive tools for the primary diagnosis of, in particular, multibacillary leprosy. A gradual, quantifiable decline in both magnitude of response and percent positive responders was observed during and after treatment. As a group, patients that developed erythema nodosum leprosum (ENL) had a significantly higher response at diagnosis than patients that either developed reversal reactions or did not develop reactions. Although higher initial anti-NDO-LID responses were a risk factor for ENL, neither platform, however, could reliably predict the time of emergence of reactional episodes.