Defining protective responses to pathogens: cytokine profiles in leprosy lesions

Leprosy Classification, Clinical Features, Epidemiology, and Host Immunological Responses: Failure of Eradication in 2023

Leprosy is of big concern in the medical fraternity. Leprosy is also known as Hansen's disease. It is a curable communicable disease that remains prevalent in most countries all over the globe. It is a chronic granulomatous infection commonly caused by Mycobacterium leprae and Mycobacterium lepromatosis, which mainly show an effect on the skin and peripheral nerves. To control the disease and minimize the impact of the disease, much effort has been put into it for decades. Nearly 0.2 million fresh cases were documented in 2017 worldwide in spite of being declared "eradicated" by the WHO in the year 2000. However, impressive achievements have been made in several countries, including India; still, we are lagging behind the ultimate goal of the final disappearance of leprosy. Extensive migration is a crucial element that may transmit leprosy to unaffected areas. Additionally, there are several areas in the USA where person-to-person leprosy transmission has been reported without a prior history of exposure. Recently, WHO instigated a new Global Leprosy Strategy 2021-2030, termed "Towards Zero Leprosy." In this article, we review the clinical features, leprosy epidemiology, transmission, classification, host immunological response, and diagnostic challenges.

Host Immune-Metabolic Adaptations Upon Mycobacterial Infections and Associated Co-Morbidities

Mycobacterial diseases are a major public health challenge. Their causative agents include, in order of impact, members of the Mycobacterium tuberculosis complex (causing tuberculosis), Mycobacterium leprae (causing leprosy), and non-tuberculous mycobacterial pathogens including Mycobacterium ulcerans. Macrophages are mycobacterial targets and they play an essential role in the host immune response to mycobacteria. This review aims to provide a comprehensive understanding of the immune-metabolic adaptations of the macrophage to mycobacterial infections. This metabolic rewiring involves changes in glycolysis and oxidative metabolism, as well as in the use of fatty acids and that of metals such as iron, zinc and copper. The macrophage metabolic adaptations result in changes in intracellular metabolites, which can post-translationally modify proteins including histones, with potential for shaping the epigenetic landscape. This review will also cover how critical tuberculosis co-morbidities such as smoking, diabetes and HIV infection shape host metabolic responses and impact disease outcome. Finally, we will explore how the immune-metabolic knowledge gained in the last decades can be harnessed towards the design of novel diagnostic and therapeutic tools, as well as vaccines.

Targeting Autophagy as a Strategy for Developing New Vaccines and Host-Directed Therapeutics Against Mycobacteria

Mycobacterial disease is an immense burden worldwide. This disease group includes tuberculosis, leprosy (Hansen's disease), Buruli Ulcer, and non-tuberculous mycobacterial (NTM) disease. The burden of NTM disease, both pulmonary and ulcerative, is drastically escalating globally, especially in developed countries such as America and Australia. Mycobacteria's ability to inhibit or evade the host immune system has contributed significantly to its continued prevalence. Pre-clinical studies have highlighted promising candidates that enhance endogenous pathways and/or limit destructive host responses. Autophagy is a cell-autonomous host defense mechanism by which intracytoplasmic cargos can be delivered and then destroyed in lysosomes. Previous studies have reported that autophagy-activating agents, small molecules, and autophagy-activating vaccines may be beneficial in restricting intracellular mycobacterial infection, even with multidrug-resistant strains. This review will examine how mycobacteria evade autophagy and discusses how autophagy could be exploited to design novel TB treatment strategies, such as host-directed therapeutics and vaccines, against Mycobacterium tuberculosis and NTMs.

The role of oxidized phospholipids in the development of disease

Oxidized phospholipids (OxPLs), complex mixtures of phospholipid oxidation products generated during normal or pathological processes, are increasingly recognized to show bioactive effects on many cellular signalling pathways. There is a growing body of evidence showing that OxPLs play an important role in many diseases, so it is essential to define the specific role of OxPLs in different diseases for the design of disease therapies. In vastly diverse pathological processes, OxPLs act as pro-inflammatory agents and contribute to the progression of many diseases; in addition, they play a role in anti-inflammatory processes, promoting the dissipation of inflammation and inhibiting the progression of some diseases. In addition to participating in the regulation of inflammatory responses, OxPLs affect the occurrence and development of diseases through other pathways, such as apoptosis promotion. In this review, the different and even opposite effects of different OxPL molecular species are discussed. Furthermore, the specific effects of OxPLs in various diseases, as well as the receptor and cellular mechanisms involved, are summarized.

Immunology of leprosy and diagnostic challenges

Leprosy, caused by noncultivable Mycobacterium leprae (ML), has varied manifestations, which are associated with the host immune responses. The dermal involvement is accompanied by peripheral nerve damage, which leads to sensory motor loss and deformities. Both innate and acquired immune responses are involved. The main cell to be compromised is the CD4 + T helper cell, which shows antigen specific unresponsiveness to only ML and not to other common antigens in the bacilliferous generalized lepromatous form of the disease. In contrast, the paucibacillary localized tuberculoid form shows appropriate T cell functions and poor antibody response. The dichotomy between T cell functions and antibodies are discussed against the current information on cytokines, Th subsets, and regulatory T cells. During lepromatous reactions, there is a temporary, heightened T cell immunity, even in lepromatous subjects. The dermal lesions confirm many features observed with peripheral blood mononuclear cells and give additional information on local immune responses. Nerve damage involves both immune and nonimmune mechanisms. Leprosy is a model disease for understanding host immune responses to intracellular bacilli. There are challenges in diagnosing early leprosy. In spite of intensive efforts by many groups, consensus on a universal test suitable for endemic areas is awaited.

Leprosy and the human genome

Despite the availability of effective treatment for several decades, leprosy remains an important medical problem in many regions of the world. Infection with Mycobacterium leprae can produce paucibacillary disease, characterized by well-formed granulomas and a Th1 T-cell response, or multibacillary disease, characterized by poorly organized cellular infiltrates and Th2 cytokines. These diametric immune responses confer states of relative resistance or susceptibility to leprosy, respectively, and have well-defined clinical manifestations. As a result, leprosy provides a unique opportunity to dissect the genetic basis of human in vivo immunity. A series of studies over the past 40 years suggests that host genes influence the risk of leprosy acquisition and the predilection for different clinical forms of the disease. However, a comprehensive, cellular, and molecular view of the genes and variants involved is still being assembled. In this article, we review several decades of human genetic studies of leprosy, including a number of recent investigations. We emphasize genetic analyses that are validated by the replication of the same phenotype in independent studies or supported by functional experiments demonstrating biological mechanisms of action for specific polymorphisms. Identifying and functionally exploring the genetic and immunological factors that underlie human susceptibility to leprosy have yielded important insights into M. leprae pathogenesis and are likely to advance our understanding of the immune response to other pathogenic mycobacteria. This knowledge may inform new treatment or vaccine strategies for leprosy or tuberculosis.

Innate immunity: a cutaneous perspective

The first responsibility for protection against microbial infection rests on the normal function of the innate immune system. This system establishes an antimicrobial barrier, recognizes attempts to breach this barrier, and responds rapidly to danger, all based on an innate defense system. Here, we review this system as it applies to mammalian skin, highlighting how a physical, cellular, and chemical barrier is formed to resist infection. When challenged, the diverse cellular components of the skin recognize the nature of the challenge and respond with an appropriate antimicrobial program including the release of antimicrobial peptides and, when necessary, recruitment and coordination with adaptive immune responses. Recent insights into these processes have advanced the understanding of disease pathogenesis and provided new therapeutic options for a variety of skin diseases.

Serum levels of interferon-gamma, tumour necrosis factor-alpha, soluble interleukin-6R and soluble cell activation markers for monitoring response to treatment of leprosy reactions

Identifying pathogen and host-related laboratory parameters are essential for the early diagnosis of leprosy reactions. The present study aimed to clarify the validity of measuring the profiles of serum cytokines [interleukin (IL)-4, IL-6, IL-10, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha], the soluble IL-6 receptor (sIL-6R), soluble T cell (sCD27) and macrophage (neopterin) activation markers and Mycobacterium leprae-specific anti-PGL-I IgM antibodies in relation to the leprosy spectrum and reactions. Serum samples from 131 Indonesian leprosy patients (82 non-reactional leprosy patients and 49 reactional) and 112 healthy controls (HC) from the same endemic region were investigated. Forty-four (89.8%) of the reactional patients had erythema nodosum leprosum (ENL) while only five (10.2%) had reversal reaction (RR). Follow-up serum samples after corticosteroid treatment were also obtained from 17 of the patients with ENL and one with RR. A wide variability in cytokine levels was observed in the patient groups. However, IFN-gamma and sIL-6R were elevated significantly in ENL compared to non-ENL patients. Levels of IFN-gamma, TNF-alpha and sIL-6R declined significantly upon corticosteroid treatment of ENL. Thus, although the present study suggests limited applicability of serial measurement of IFN-gamma, TNF-alpha and sIL-6R in monitoring treatment efficacy of ENL, reactions it recommends a search for a wider panel of more disease-specific markers in future studies.

Th1/Th2 cytokine profiles and their relationship to clinical features in patients following nonmyeloablative allogeneic stem cell transplantation

An imbalance in helper T-cell type 1 (Th1) and type 2 (Th2) cytokines is suggested to play an important role in the pathogenesis of acute graft-versus-host disease (aGVHD). The aim of this study was to investigate the cytokine bias acquired by T cells after transplantation and its possible influence on relapse of original malignancy. Cytokine levels by peripheral CD4 and CD8 T cells were tested at various pre- and post-transplant time points with fluorescein isothiocyanate-based intracellular cytokine assay after short-term in vitro mitogenic stimulation (phorbol myristate acetate + ionomycin). In both CD4+ and CD8+ cells, interferon (IFN)-gamma-producing cell populations increased, indicating a shift to a Th1 cytokine profile with aGVHD. IFN-gamma-producing T cells was significantly lower in patients who experienced relapse of original disease compared to those who showed no signs of relapse and compared to normal controls. Our studies demonstrate that aGVHD correlates with a Th1 bias and that Th1 response may potentiate an effective immune surveillance.

Th1/Th2 cytokine expression and its relationship with tumor growth in B cell non-Hodgkin's lymphoma (NHL)

AT helper 1 (Th1) immune response is considered more effective than T helper 2 (Th2) for anti-tumor immunity, but either response could potentially stimulate tumor cell growth in lymphomas. Moreover, both IL-4 and IL-2/IL-12 are used in experimental treatment models for non-Hodgkin's lymphoma (NHL) despite their differing ability to elicit Th2 or Th1 responses, respectively. Here, we investigate which T helper cytokines (Th1 or Th2) predominate in B cell NHL tissue and determine whether cytokine expression correlates with tumor cell growth, cell death, and survival in a series of 44 NHL patients. Overall, we observed both Th1 and Th2 cytokine expression at the mRNA level, detecting high levels of IFN-gamma, IL6 and IL-10 expression in the majority of tumors. Transcripts for the IL-12 subunits p35 (38 of 38) and p 40 (23 of 38) were frequently detected in NHL tissue, and high p40 levels were common in patients with a good prognosis. Furthermore, high IL-4 levels correlated with greater survival duration (P < 0.0024) but nor overall survival. Cytokine expression of IL-2, IFNgamma and IL-4 was significantly reduced in the high grade tumor group. Interestingly, there was a strong correlation between high IL-4 levels and reduced levels of apoptosis (P < 0.006) or proliferation (P < 0.0001), which has also been reported in leukemic models. This has important implications for the success of IL-4 as a treatment for low and high grade tumors.

Cytokine profile of liver- and blood-derived nonspecific T cells after liver transplantation: T helper cells type 1/0 lymphokines dominate in recurrent hepatitis C virus infection and rejection

Orthotopic liver transplantation (OLT) is a successful treatment in patients with hepatitis C virus (HCV)-associated end-stage liver disease worldwide. T lymphocytes and their cytokines are believed to have a pivotal role in the defense against HCV and in allograft rejection. An immunosuppressive drug regimen may cause a cytokine imbalance toward a T helper (TH) cell type 2 profile that is associated with the persistence of infection and acceptance of the graft. The aim of this study is to assess whether cytokine imbalances toward a TH1- or TH2-type response may have a role in recurrent HCV infection and rejection after OLT. Twenty-one intrahepatic T-cell lines of 15 patients with recurrent HCV infection after OLT (group A) and 15 lines of 11 patients with rejection (group B) were studied. Both patient groups had received liver allografts because of HCV-associated end-stage liver disease. Patients with HCV-induced liver disease who did not undergo OLT served as controls: 17 patients with chronic hepatitis C (CH-C) and 8 patients with cirrhosis. At the time of liver biopsy, 14 blood-derived T-cell lines of 12 patients with recurrent HCV infection, 7 of 10 patients with rejection, and 18 of 18 control patients were also investigated. Regardless of the underlying disease (recurrent HCV infection, rejection, HCV-induced hepatitis, and cirrhosis), all liver tissue-derived T-cell lines produced interferon-gamma; some additionally produced interleukin-4 (IL-4), but none produced IL-10, indicating that the TH0/1 cytokine profile dominates. T-cell lines showing a TH1 cytokine profile derived from intrahepatic T cells could be established significantly more often in recurrent HCV infection and rejection than in controls with CH-C (Fisher's exact test, P <.05). The cytokine profile of intrahepatic T cells did not differ from that obtained in peripheral blood. TH0/1 cytokine profile dominates the intrahepatic and blood-derived immune response in recurrent HCV infection and rejection after OLT regardless of the mode of immunosuppression. The lymphokine profile of immunocompromised patients with recurrent HCV infection or rejection does not differ principally from that of patients with HCV-induced hepatitis and cirrhosis, but seems to show a TH1 profile significantly more often.

Generation and in vivo persistence of polarized Th1 and Th2 memory cells

In vitro generated CD4 cell lines and effectors often produce either Th1 or Th2 cytokines, but stimulation of resting CD4 cells from animals leads to production mostly of IL-2. To determine whether polarization of CD4 effector cells results in development of polarized memory, I generated antigen-specific Th1 and Th2 effectors in vitro and transferred them to adoptive hosts. The effectors gave rise to long-lived populations of CD4 T cells with the phenotype of resting memory cells. Recovered cells responded vigorously to specific antigen, producing a pattern of cytokines closely related to that of the transferred effectors. Thus, encounter with a peptide antigen and directive cytokines at the initiation of culture can lead to generation of both effector and long-lived memory cell populations that produce restricted patterns of cytokines.