Analysis of naturally occurring delayed-type hypersensitivity reactions in leprosy by in situ hybridization

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.

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.

The cellular architecture of the antimicrobial response network in human leprosy granulomas

Granulomas are complex cellular structures composed predominantly of macrophages and lymphocytes that function to contain and kill invading pathogens. Here, we investigated the single-cell phenotypes associated with antimicrobial responses in human leprosy granulomas by applying single-cell and spatial sequencing to leprosy biopsy specimens. We focused on reversal reactions (RRs), a dynamic process whereby some patients with disseminated lepromatous leprosy (L-lep) transition toward self-limiting tuberculoid leprosy (T-lep), mounting effective antimicrobial responses. We identified a set of genes encoding proteins involved in antimicrobial responses that are differentially expressed in RR versus L-lep lesions and regulated by interferon-γ and interleukin-1β. By integrating the spatial coordinates of the key cell types and antimicrobial gene expression in RR and T-lep lesions, we constructed a map revealing the organized architecture of granulomas depicting compositional and functional layers by which macrophages, T cells, keratinocytes and fibroblasts can each contribute to the antimicrobial response.

Cellular, Molecular, and Immunological Characteristics of Langhans Multinucleated Giant Cells Programmed by IL-15

Langhans multinucleated giant cells (LGCs) are a specific type of multinucleated giant cell containing a characteristic horseshoe-shaped ring of nuclei that are present within granulomas of infectious etiology. Although cytokines that trigger macrophage activation (such as IFN-γ) induce LGC formation, it is not clear whether cytokines that trigger macrophage differentiation contribute to LGC formation. Here, we found that IL-15, a cytokine that induces M1 macrophage differentiation, programs human peripheral blood adherent cells to form LGCs. Analysis of the IL-15‒treated adherent cell transcriptome identified gene networks for T cells, DNA damage and replication, and IFN-inducible genes that correlated with IL-15 treatment and LGC-type multinucleated giant cell formation. Gene networks enriched for myeloid cells were anticorrelated with IL-15 treatment and LGC formation. Functional studies revealed that T cells were required for IL-15‒induced LGC formation, involving a direct contact with myeloid cells through CD40L-CD40 interaction and IFN-γ release. These data indicate that IL-15 induces LGC formation through the direct interaction of activated T cells and myeloid cells.

Identification of a systemic interferon-γ inducible antimicrobial gene signature in leprosy patients undergoing reversal reaction

Reversal reactions (RRs) in leprosy are characterized by a reduction in the number of bacilli in lesions associated with an increase in cell-mediated immunity against the intracellular bacterium Mycobacterium leprae, the causative pathogen of leprosy. To identify the mechanisms that contribute to cell-mediated immunity in leprosy, we measured changes in the whole blood-derived transcriptome of patients with leprosy before, during and after RR. We identified an ‘RR signature’ of 1017 genes that were upregulated at the time of the clinical diagnosis of RR. Using weighted gene correlated network analysis (WGCNA), we detected a module of 794 genes, bisque4, that was significantly correlated with RR, of which 434 genes were part of the RR signature. An enrichment for both IFN-γ and IFN-β downstream gene pathways was present in the RR signature as well as the RR upregulated genes in the bisque4 module, including those encoding proteins of the guanylate binding protein (GBP) family that contributes to antimicrobial responses against mycobacteria. Specifically, GBP1, GBP2, GBP3 and GBP5 mRNAs were upregulated in the RR peripheral blood transcriptome, with GBP1, GBP2 and GBP5 mRNAs also upregulated in the RR disease lesion transcriptome. These data indicate that RRs involve a systemic upregulation of IFN-γ downstream genes including GBP family members as part of the host antimicrobial response against mycobacteria.

Reversal reaction (RR) is a major cause of tissue injury and disabilities in leprosy, resulting from the rapid onset of cell-mediated immune responses to the intracellular bacterium Mycobacterium leprae. To identify the mechanisms related to the increase in cell-mediated immunity in RR, we measured changes in the whole blood-derived transcriptome of patients with leprosy before, during and after RR. We identified that RRs are associated with an IFN-γ induced inflammatory response including an antimicrobial gene network containing the GBP1, GBP2, GBP3 and GBP5 mRNAs in the peripheral blood. Furthermore, we show that GBP1, GBP2 and GBP5 mRNAs are also upregulated at the site of disease in RR patients. In summary, our study suggests that RR involves a systemic induction of IFN-γ regulated genes that contributes to an antimicrobial response against the pathogen, releasing ligands and antigens that can further amplify the inflammatory response.

Autophagy links antimicrobial activity with antigen presentation in Langerhans cells

DC, through the uptake, processing, and presentation of antigen, are responsible for activation of T cell responses to defend the host against infection, yet it is not known if they can directly kill invading bacteria. Here, we studied in human leprosy, how Langerhans cells (LC), specialized DC, contribute to host defense against bacterial infection. IFN-γ treatment of LC isolated from human epidermis and infected with Mycobacterium leprae (M. leprae) activated an antimicrobial activity, which was dependent on the upregulation of the antimicrobial peptide cathelicidin and induction of autophagy. IFN-γ induction of autophagy promoted fusion of phagosomes containing M. leprae with lysosomes and the delivery of cathelicidin to the intracellular compartment containing the pathogen. Autophagy enhanced the ability of M. leprae-infected LC to present antigen to CD1a-restricted T cells. The frequency of IFN-γ labeling and LC containing both cathelicidin and autophagic vesicles was greater in the self-healing lesions vs. progressive lesions, thus correlating with the effectiveness of host defense against the pathogen. These data indicate that autophagy links the ability of DC to kill and degrade an invading pathogen, ensuring cell survival from the infection while facilitating presentation of microbial antigens to resident T cells.

The Effects of Prednisolone Treatment on Cytokine Expression in Patients with Erythema Nodosum Leprosum Reactions

Erythema nodosum leprosum (ENL) is a systemic inflammatory complication occurring mainly in patients with lepromatous leprosy (LL) and borderline lepromatous leprosy. Prednisolone is widely used for treatment of ENL reactions but clinical improvement varies. However, there is little good in vivo data as to the effect of prednisolone treatment on the pro-inflammatory cytokines in patients with ENL reactions. As a result, treatment and management of reactional and post-reactional episodes of ENL often pose a therapeutic challenge. We investigated the effect of prednisolone treatment on the inflammatory cytokines TNF, IFN-γ, IL-1β, IL-6, and IL-17 and the regulatory cytokines IL-10 and TGF-β in the skin lesion and blood of patients with ENL and compared with non-reactional LL patient controls. A case–control study was employed to recruit 30 patients with ENL and 30 non-reactional LL patient controls at ALERT Hospital, Ethiopia. Blood and skin biopsy samples were obtained from each patient before and after prednisolone treatment. Peripheral blood mononuclear cells from patients with ENL cases and LL controls were cultured with M. leprae whole-cell sonicates (MLWCS), phytohemagglutinin or no stimulation for 6 days. The supernatants were assessed with the enzyme-linked immunosorbent assay for inflammatory and regulatory cytokines. For cytokine gene expression, mRNA was isolated from whole blood and skin lesions and then reverse transcribed into cDNA. The mRNA gene expression was quantified on a Light Cycler using real-time PCR assays specific to TNF, IFN-γ, IL-β, TGF-β, IL-17A, IL-6, IL-8, and IL-10. The ex vivo production of the cytokines: TNF, IFN-γ, IL-1β, and IL-17A was significantly increased in untreated patients with ENL. However, IL-10 production was significantly lower in untreated patients with ENL and significantly increased after treatment. The ex vivo production of IL-6 and IL-8 in patients with ENL did not show statistically significant differences before and after prednisolone treatment. The mRNA expression in blood and skin lesion for TNF, IFN-γ, IL-1β, IL-6, and IL-17A significantly reduced in patients with ENL after treatment, while mRNA expression for IL-10 and TGF-β was significantly increased both in blood and skin lesion after treatment. This is the first study examining the effect of prednisolone on the kinetics of inflammatory and regulatory cytokines in patients with ENL reactions before and after prednisolone treatment. Our findings suggest that prednisolone modulates the pro-inflammatory cytokines studied here either directly or through suppression of the immune cells producing these inflammatory cytokines.

New Insight into the Pathogenesis of Erythema Nodosum Leprosum: The Role of Activated Memory T-Cells

Memory T-cells, particularly, effector memory T cells are implicated in the pathogenesis of inflammatory diseases and may contribute to tissue injury and disease progression. Although erythema nodosum leprosum (ENL) is an inflammatory complication of leprosy, the role of memory T cell subsets has never been studied in this patient group. The aim of this study was at investigate the kinetics of memory T cell subsets in patients with ENL before and after prednisolone treatment. A case–control study design was used to recruit 35 untreated patients with ENL and 25 non-reactional lepromatous leprosy (LL) patient controls at ALERT Hospital, Ethiopia. Venous blood samples were obtained before, during, and after treatment from each patient. Peripheral blood mononuclear cells (PBMCs) were isolated and used for immunophenotyping of T cell activation and memory T-cell subsets by flow cytometry. The kinetics of these immune cells in patients with ENL before and after treatment were compared with LL patient controls as well as within ENL cases at different time points. The median percentage of CD3⁺, CD4⁺, and CD8⁺ T-cells expressing activated T-cells were significantly higher in the PBMCs from patients with ENL than from LL patient controls before treatment. The median percentage of central and activated memory T-cells was significantly increased in patients with ENL compared to LL patient controls before treatment. Interestingly, patients with ENL had a lower percentage of naïve T cells (27.7%) compared to LL patient controls (59.5%) (P < 0.0001) before treatment. However, after prednisolone treatment, patients with ENL had a higher median percentage of naïve T-cells (43.0%) than LL controls (33.0%) (P < 0.001). The median percentage of activated T-cells (effector memory and effector T-cells) was significantly increased in patients with ENL (59.2%) before treatment compared to after treatment with prednisolone (33.9%) (P < 0.005). This is the first work which has shown T-cell activation and the different subsets of memory T cells in untreated patients with ENL. Consequently, this study delineates the role of T-cell activation in the pathogenesis of ENL reaction and challenges the long-standing dogma of immune complex as a sole etiology of ENL reaction.

TB or not TB: that is no longer the question

Tuberculosis (TB) remains a devastating infectious disease and, with the emergence of multidrug-resistant forms, represents a major global threat. Much of our understanding of pathogenic and immunologic mechanisms in TB has derived from studies in experimental animals. However, it is becoming increasingly clear in TB as well as in other inflammatory diseases that there are substantial differences in immunological responses of humans not found or predicted by animal studies. Thus, it is critically important to understand mechanisms of pathogenesis and immunological protection in humans. In this review, we will address the key immunological question: What are the necessary and sufficient immune responses required for protection against TB infection and disease in people-specifically protection against infection, protection against the establishment of latency or persistence, and protection against transitioning from latent infection to active disease.

Gene set signature of reversal reaction type I in leprosy patients

Leprosy reversal reactions type 1 (T1R) are acute immune episodes that affect a subset of leprosy patients and remain a major cause of nerve damage. Little is known about the relative importance of innate versus environmental factors in the pathogenesis of T1R. In a retrospective design, we evaluated innate differences in response to Mycobacterium leprae between healthy individuals and former leprosy patients affected or free of T1R by analyzing the transcriptome response of whole blood to M. leprae sonicate. Validation of results was conducted in a subsequent prospective study. We observed the differential expression of 581 genes upon exposure of whole blood to M. leprae sonicate in the retrospective study. We defined a 44 T1R gene set signature of differentially regulated genes. The majority of the T1R set genes were represented by three functional groups: i) pro-inflammatory regulators; ii) arachidonic acid metabolism mediators; and iii) regulators of anti-inflammation. The validity of the T1R gene set signature was replicated in the prospective arm of the study. The T1R genetic signature encompasses genes encoding pro- and anti-inflammatory mediators of innate immunity. This suggests an innate defect in the regulation of the inflammatory response to M. leprae antigens. The identified T1R gene set represents a critical first step towards a genetic profile of leprosy patients who are at increased risk of T1R and concomitant nerve damage.

Leprosy type 1 reversal reactions (T1R) are an important cause of nerve damage in leprosy patients and accurate prediction of patients at increased risk of T1R is a major challenge of current leprosy control. The incidence of T1R differs widely from 6% to 67% of leprosy patients in different leprosy endemic settings. Whether or not this reflects the impact of unknown environmental triggers or differences in the genetic background across ethnicities is not known. We performed a comparative transcriptome analysis between leprosy patients affected and free of T1R in response to M. leprae antigens. As the discovery sample we enrolled cured leprosy patients who had been diagnosed with T1R at the time of leprosy diagnosis and leprosy patients who had never undergone T1R (retrospective arm). Whole genome transcriptome analysis after stimulation of blood with M. leprae antigen resulted in the definition of a T1R signature gene set. We validated the T1R gene set in RNA samples obtained from T1R-free patients at the time of leprosy diagnosis and followed for 3 years for development of T1R (prospective arm). These results confirm the role of innate factors in T1R and are a first step towards a predictive genetic T1R signature.

Type I interferon suppresses type II interferon-triggered human anti-mycobacterial responses

Type I interferons (IFN-α and IFN-β) are important for protection against many viral infections, whereas type II interferon (IFN-γ) is essential for host defense against some bacterial and parasitic pathogens. Study of IFN responses in human leprosy revealed an inverse correlation between IFN-β and IFN-γ gene expression programs. IFN-γ and its downstream vitamin D-dependent antimicrobial genes were preferentially expressed in self-healing tuberculoid lesions and mediated antimicrobial activity against the pathogen Mycobacterium leprae in vitro. In contrast, IFN-β and its downstream genes, including interleukin-10 (IL-10), were induced in monocytes by M. leprae in vitro and preferentially expressed in disseminated and progressive lepromatous lesions. The IFN-γ-induced macrophage vitamin D-dependent antimicrobial peptide response was inhibited by IFN-β and by IL-10, suggesting that the differential production of IFNs contributes to protection versus pathogenesis in some human bacterial infections.

Galectin-3 regulates the innate immune response of human monocytes

Galectin-3 is a β-galactoside-binding lectin widely expressed on epithelial and hematopoietic cells, and its expression is frequently associated with a poor prognosis in cancer. Because it has not been well-studied in human infectious disease, we examined galectin-3 expression in mycobacterial infection by studying leprosy, an intracellular infection caused by Mycobacterium leprae. Galectin-3 was highly expressed on macrophages in lesions of patients with the clinically progressive lepromatous form of leprosy; in contrast, galectin-3 was almost undetectable in self-limited tuberculoid lesions. We investigated the potential function of galectin-3 in cell-mediated immunity using peripheral blood monocytes. Galectin-3 enhanced monocyte interleukin 10 production to a TLR2/1 ligand, whereas interleukin 12p40 secretion was unaffected. Furthermore, galectin-3 diminished monocyte to dendritic cell differentiation and T-cell antigen presentation. These data demonstrate an association of galectin-3 with unfavorable host response in leprosy and a potential mechanism for impaired host defense in humans.

A role for interleukin-5 in promoting increased immunoglobulin M at the site of disease in leprosy

Leprosy is an infectious disease in which the clinical manifestations correlate with the type of immune response mounted to the pathogen, Mycobacterium leprae. To investigate which biological pathways or gene sets are over-represented in lepromatous (L-Lep) versus tuberculoid (T-Lep) patients that might be relevant in disease pathogenesis, we compared the gene expression profiles of L-lep versus T-lep skin lesions using knowledge-guided bioinformatic analysis, incorporating data on likely biological functions, including gene ontology information and regulatory data. Analysis of probe sets comparatively increased in expression in L-lep versus T-lep revealed multiple pathways and functional groups involving B-cell genes (P values all < 0.005) relevant to the dataset. Further pathways analysis of B-cell genes comparatively increased in expression in L-lep versus T-lep lesions revealed a potential network linking the expression of immunoglobulin M (IgM) and interleukin-5 (IL-5). Analysis of the leprosy lesions by immunohistology indicated that there was approximately 8% more IgM-positive cells in L-lep lesions than in T-lep lesions. Furthermore, IL-5 synergized in vitro with M. leprae to enhance total IgM secretion from peripheral blood mononuclear cells. This pathways analysis of leprosy in combination with our in vitro studies implicates a role for IL-5 in the increased IgM at the site of disease in leprosy.

Reactions following completion of 1 and 2 year multidrug therapy (MDT)

We evaluated the incidence, severity, and duration of reactional states in 139 multibacillary (MB) leprosy patients in the first 2 years after the completion of the 1 year regimen of multidrug therapy (MDT) currently recommended by the World Health Organization (WHO) and compared those findings with 295 MB leprosy patients treated with the same regimen previously recommended for 2 years. During the first year after the completion of 1 year MDT, patients experienced 1 or more reactional states 27% of the time, the vast majority being lepra type 1 reactions (reversal reactions, RR), whereas patients who received 2 year MDT experienced a reactional state during that time period only 8% of the time (P < 0.001). Furthermore, during the first year after the completion of therapy, and during the first 2 years, both the number of reactional states and reversal reactions were significantly (P < or = 0.004) more frequent, severe, of longer duration, and more commonly associated with neuritis.

The innate immune response in leprosy

Investigation into the innate immune response in leprosy has provided insight into immunoregulation in human infectious disease. Key advances include the role of pattern recognition receptors in recognizing pathogen-associated molecular patterns of Mycobacterium leprae, cytokine release by innate immune cells, macrophage and dendritic cell differentiation, as well as antimicrobial effector pathways. These insights provide targets for therapeutic intervention in modulating the course of leprosy and other chronic infectious diseases.

Towards understanding the pathology of erythema nodosum leprosum

Erythema nodosum leprosum (ENL) is an immune-mediated complication of leprosy presenting with inflammatory skin nodules and involvement of multiple organ systems, often running a protracted course. Immune complex production and deposition as well as complement activation have long been regarded as the principal aetiology of ENL. However, new data show that cell-mediated immunity is also important. We have performed a critical analysis of studies on the pathology of ENL. Our main findings are as follows. ENL is characterised by an inflammatory infiltrate of neutrophils with vasculitis and/or panniculitis. There is deposition of immune complexes and complement together with Mycobacterium leprae antigens in the skin. Changes in serum levels of Igs indicate a transient, localised immune response. The major T-cell subtype in ENL is the CD4 cell, in contrast to lepromatous leprosy where CD8 cells predominate. The cytokines TNFalpha and IL-6 are consistently found whilst IL-4 is low or absent in ENL lesions, indicating a T(H)1 type response. Keratinocyte 1a and intercellular adhesion molecule-1 (ICAM-1) have been shown to be present in the epidermis in ENL, which is evidence of a cell-mediated immune response. Co-stimulatory molecules such as B7-1 have also been studied but further work is needed to draw strong conclusions. We also highlight potential areas for future research.

Two patients coinfected with Mycobacterium leprae and human immunodeficiency virus type 1 and naive for antiretroviral therapy who exhibited type 1 leprosy reactions mimicking the immune reconstitution inflammatory syndrome

Two case reports of patients with human immunodeficiency virus type 1 (HIV-1) infection who developed leprosy are presented. Both developed type 1 leprosy reactions in the absence of antiretroviral therapy. Reactions have been described for a number of HIV-1- and Mycobacterium leprae-coinfected patients and have been considered to be part of an immune reconstitution inflammatory syndrome (IRIS) since the reactions were usually linked to the administration of highly active antiretroviral therapy. The reports of our two patients suggest that the type 1 reactions in patients with leprosy and HIV may not always be an IRIS manifestation but may be akin to the classical reactional state described for the natural course of leprosy infection, which occurs in leprosy patients due to the fluctuations of the antimycobacterial immune response, whether they are coinfected with HIV or not.

Interactions between HIV infection and leprosy: a paradox

Early in the HIV epidemic it was feared that the disease would undermine leprosy control, as has occurred with tuberculosis. It was predicted that patients with leprosy and HIV coinfection would have an increased risk of lepromatous disease and a faster clinical evolution, and that the leprosy would be more difficult to treat. None of these concerns have materialised and the interaction between HIV and Mycobacterium leprae seems to be far more subtle than that between HIV and tuberculosis. We review the epidemiological, clinical, and pathological data relating to leprosy/HIV coinfection. The published epidemiological data are limited in quality but show neither an increased HIV prevalence among leprosy cases nor an alteration in clinical spectrum of leprosy among coinfected patients. Some data suggest that immune-mediated reactions that complicate leprosy occur at a higher frequency in coinfected patients. Leprosy has now been reported presenting as immune reconstitution disease among patients commencing highly active antiretroviral treatment. Histopathological observations reveal a normal spectrum of appearances in biopsies of leprosy lesions from coinfected patients, even among those with advanced immunodeficiency. These observations suggest that cell-mediated immune responses to M leprae are preserved at the site of disease despite evidence that these responses are abrogated systemically, by contrast with tuberculosis, in which the host granulomatous response is impaired by HIV coinfection. We speculate that this paradox may relate to differences between the activation state and rates of cell turnover within leprosy and tuberculosis granulomas that differentially affect the susceptibility of the granulomas to HIV. The interactions between leprosy and HIV have been little studied and further research on the clinical, pathological, and management aspects of this coinfection is warranted.

High levels of inflammatory cytokines are associated with poor clinical response to steroid treatment and recurrent episodes of type 1 reactions in leprosy

Levels of leprosy antigen-induced interferon-gamma (IFN-gamma), tumour necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) were measured in 96 leprosy patients with type 1 reactions (T1R) before, during and after a standard 12-week course of steroids. Peripheral blood mononuclear cells (PBMC) from leprosy patients with untreated T1R produced significantly more TNF-alpha than leprosy patients without T1R. Median levels of IFN-gamma and TNF-alpha in T1R patients fell during treatment with steroids; however, TNF-alpha levels increased as the steroid dose was reduced. Median IL-10 levels increased throughout the steroid treatment period and were associated strongly with TNF-alpha levels. Patients with high cytokine levels had a poorer recovery of sensory or voluntary muscle nerve function, a higher risk of reactivation of symptoms during steroid treatment, and a higher risk of another episode of T1R within 2 months of completing the steroid regimen. Rapid and effective reversal of the inflammatory process in T1R is critical to prevent permanent nerve damage from T1R and monitoring cytokine levels during treatment may be useful.

Mycobacterium leprae-specific, HLA class II-restricted killing of human Schwann cells by CD4+ Th1 cells: a novel immunopathogenic mechanism of nerve damage in leprosy

Peripheral nerve damage is a major complication of reversal (or type-1) reactions in leprosy. The pathogenesis of nerve damage remains largely unresolved, but detailed in situ analyses suggest that type-1 T cells play an important role. Mycobacterium leprae is known to have a remarkable tropism for Schwann cells of the peripheral nerve. Reversal reactions in leprosy are often accompanied by severe and irreversible nerve destruction and are associated with increased cellular immune reactivity against M. leprae. Thus, a likely immunopathogenic mechanism of Schwann cell and nerve damage in leprosy is that infected Schwann cells process and present Ags of M. leprae to Ag-specific, inflammatory type-1 T cells and that these T cells subsequently damage and lyse infected Schwann cells. Thus far it has been difficult to study this directly because of the inability to grow large numbers of human Schwann cells. We now have established long-term human Schwann cell cultures from sural nerves and show that human Schwann cells express MHC class I and II, ICAM-1, and CD80 surface molecules involved in Ag presentation. Human Schwann cells process and present M. leprae, as well as recombinant proteins and peptides to MHC class II-restricted CD4(+) T cells, and are efficiently killed by these activated T cells. These findings elucidate a novel mechanism that is likely involved in the immunopathogenesis of nerve damage in leprosy.

Immunohistochemical analysis of cellular infiltrate and gamma interferon, interleukin-12, and inducible nitric oxide synthase expression in leprosy type 1 (reversal) reactions before and during prednisolone treatment

The effects of prednisolone treatment on the cellularity and cytokine (gamma interferon, interleukin-12, and inducible nitric oxide synthase) profiles of leprosy skin type 1 (reversal) reactions were studied using immunohistochemistry. Skin biopsies were taken from 15 patients with leprosy type 1 (reversal) reactions at days 0, 7, 28, and 180 after the start of steroid treatment. Prednisolone treatment had little effect at day 7, but by day 28 significant decreases were found in cytokine levels. Some patients maintained cytokine production at days 28 and 180. These results illustrate the strong Th1 profile of type 1 reactional lesions, the slow response to steroid therapy, and continuing activity at 180 days.

Novel mechanisms in the immunopathogenesis of leprosy nerve damage: the role of Schwann cells, T cells and Mycobacterium leprae

The major complication of reversal (or type 1) reactions in leprosy is peripheral nerve damage. The pathogenesis of nerve damage remains largely unresolved. In situ analyses suggest an important role for type 1 T cells. Mycobacterium leprae is known to have a remarkable tropism for Schwann cells that surround peripheral axons. Reversal reactions in leprosy are often accompanied by severe and irreversible nerve destruction and are associated with increased cellular immune reactivity against M. leprae. Thus, a likely immunopathogenic mechanism of Schwann cell and nerve damage in leprosy is that infected Schwann cells process and present antigens of M. Leprae to antigen-specific, inflammatory type 1 T cells and that these T cells subsequently damage and lyse infected Schwann cells. Previous studies using rodent CD8+ T cells and Schwann cells have revealed evidence for the existence of such a mechanism. Recently, a similar role has been suggested for human CD4+ T cells. These cells may be more important in causing leprosy nerve damage in vivo, given the predilection of M. leprae for Schwann cells and the dominant role of CD4+ serine esterase+ Th1 cells in leprosy lesions. Antagonism of molecular interactions between M. leprae, Schwann cells and inflammatory T cells may therefore provide a rational strategy to prevent Schwann cell and nerve damage in leprosy.

Cytokine mRNA expression in leprosy: a possible role for interferon-gamma and interleukin-12 in reactions (RR and ENL)

Leprosy patients during the natural course of the disease may develop reactional episodes, namely reversal reaction (RR) and erythema nodosum leprosum (ENL). Immunological events described as occurring during RR indicate up-regulation of the immune response, whereas in ENL the events are not fully understood. The aim of this study was to analyse the in vivo pattern of cytokine gene expression in the reactional states of leprosy. Peripheral blood mononuclear cells (PBMC, n = 14) and tissue samples (n = 17) obtained from patients with ENL and RR were obtained and assayed by RT-PCR. PBMC obtained from unreactional patients (n = 15) and normal individuals (n = 5) were also assessed. Expression of interferon (IFN)gamma, granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin (IL)-2Rp55, perforin and IL-1beta mRNA in PBMC were detected mostly in ENL/RR patients, but not in unreactional patients. Likewise, cytokines such as IL-6, IL-8, tumour necrosis factor (TNF)alpha and TNFbeta were also present in reactional and tuberculoid patients as opposed to lepromatous leprosy (BL/LL). Interestingly, the majority of ENL/RR patients showed messages for IL-6, IL-10, IL-12 and TNFalpha in the skin. IFNgamma was detected in 84.6% (ENL) and 100% (RR) of the patients, whereas IL-4 was detected only in few individuals (38.5 and 25%, respectively). Although mRNA expression and protein levels may be different, the data reported in this study suggest a cytokine mRNA profile that seems to be indistinguishable for RR and ENL. In addition, it shows up-regulation of immuno-inflammatory cytokines in the blood and tissue of the same patient examined before and during reaction. Furthermore, it is suggested that this pattern of response results from an immunological reactivation that might lead to an acute inflammatory response in both reactional episodes.

Expression of interleukin-4 and interferon-gamma in the small bowel of patients with dermatitis herpetiformis and isolated gluten-sensitive enteropathy

Although possessing a morphologically similar small bowel abnormality to patients with isolated gluten-sensitive enteropathy (GSE), patients with dermatitis herpetiformis (DH) have few gastrointestinal symptoms and exhibit blistering skin lesions and cutaneous IgA deposits. To determine whether clinical discrepancies between these gluten-sensitive conditions might be the result of different patterns of small bowel cytokine expression, duodenal biopsies were obtained from eight DH patients and nine isolated GSE patients. Biopsies were evaluated for interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) expression by reverse-transcriptase polymerase chain reaction (message) and immunohistochemistry (protein). In DH patients, most of whom had no gut symptoms, IFN-gamma mRNA expression was significantly less than in isolated GSE patients with symptomatic gut disease. Conversely, IL-4 mRNA expression in DH patients was greater than that found among isolated GSE patients. These findings suggest that the different clinical phenotypes of gluten sensitivity may be caused by variation in cytokine expression in the small bowel response to gluten.

Cytokines in leprosy, I. Serum cytokine profile in leprosy

BACKGROUND

Leprosy is a chronic infectious disease characterized by a broad spectrum of clinical forms depending on the patient's immune response, in particular cell-mediated immune response.

METHODS

Cytokines can play a role in the cell-mediated immune response. Serum levels of interferon-gamma (IFN-gamma), interleukin-2 (IL-2), interleukin-2 receptor (IL-2R), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) were measured by enzyme-linked immunosorbent assay (ELISA) in 55 untreated leprosy patients and 35 reactional leprosy patients, in addition to 20 age- and sex-matched healthy controls.

RESULTS

Leprosy patients showed significantly higher serum levels of the studied cytokines (except IL-2) compared with healthy controls. When the two poles were compared, tuberculoid leprosy (TT) patients showed significantly higher levels of IFN-gamma and TNF-alpha with significant negative correlations with the bacterial index (BI), whereas lepromatous leprosy (LL) patients showed significantly higher serum levels of IL-2R, IL-10, and IL-1beta with significant positive correlations with the BI. Both type I and type II reactional patients showed significantly higher serum IFN-gamma, IL-2R, and IL-1beta, in addition to IL-10 in type II reactional patients, compared with nonreactional leprosy patients. When compared with each other, type I reactional patients showed increased levels of IFN-gamma, whereas type II reactional patients showed increased levels of IL-10.

CONCLUSIONS

In leprosy patients, both IFN-gamma and TNF-alpha are immunoprotective, whereas IL-2R, IL-10, and IL-1beta are immunosuppressive. Our results indicate that type I reaction, with increased levels of IFN-gamma, is a cell-mediated immune response, whereas type II reaction, with increased levels of IL-10, is essentially an immune complex disease.

Immunocytochemical localization of inducible nitric oxide synthase and transforming growth factor-beta (TGF-beta) in leprosy lesions

Inducible nitric oxide synthase (iNOS) and TGF-beta were localized by immunocytochemistry in skin lesions from patients across the leprosy spectrum, and from patients undergoing reversal reaction. iNOS expression was highest at the tuberculoid pole of the spectrum, and increased during reversal reaction. TGF-beta was observed throughout the leprosy spectrum, but was highest at the lepromatous pole. Levels of TGF-beta decreased during reversal reaction. Reduced levels of TGF-beta may contribute to unregulated inflammatory responses during reactional episodes.

Local expression of IFN-gamma mRNA in skin lesions of patients with dermatophytosis

Delayed type hypersensitivity (DTH) response to dermatophyte antigens is one of the host defense mechanisms in dermatophytosis. Skin lesions of dermatophytosis were examined for the cytokine mRNAs expression using the reverse transcriptase/polymerase chain reaction (RT-PCR) method. Interferon-gamma (IFN-gamma) mRNA was expressed in all of the dermatophytosis lesions. IFN-gamma plays an important role in the effector phase of the DTH reaction. Therefore, these findings indicate that DTH response is elicited in the skin lesions with dermatophytosis.

The cytokines NAP-1 (IL-8), MCP-1, IL-1 beta, and GRO in rabbit inflammatory skin lesions produced by the chemical irritant sulfur mustard

Developing and healing dermal inflammatory lesions were produced in rabbits by the topical application of dilute sulfur mustard (SM), the military vesicant. In tissue sections of such lesions, cells containing the mRNA of important cytokines were identified with in situ hybridization techniques. These cytokines were neutrophil attractant/activation protein-1 (NAP-1 (also called IL-8), monocyte chemoattractant (activating) protein 1 (MCP-1), interleukin 1 (beta) (IL-1 (beta)), and GRO (a growth factor and chemokine). Mononuclear cells (mainly macrophages and activated fibroblasts) contained the mRNA of all four of these cytokines. A higher percentage of cytokine-producing mononuclear cells (macrophages and activated fibroblasts) was present in lesions at 2 days (their peak size) than at 6 days, when they were almost healed. Granulocytes emigrated from the bloodstream, passed through the lesions, and were the major constituent of the protective crust. This sequence correlated with the distribution of cells able to produce NAP-1: At 2 days and 6 days, the mononuclears that contained messenger RNA for this granulocyte chemoattractant were found mainly in the upper part of the dermis. At 2 days and 6 days, cells containing the mRNA of IL-1, a primary cytokine, were also found predominantly in the upper dermis, i.e., nearest the site of injury. In contrast, mononuclears containing the mRNA of MCP-1 (a monocyte chemoattractant), and the mRNA of GRO (a granulocyte chemoattractant) were more equally distributed throughout the dermis. SM stimulated hair follicle epithelial cells to up-regulate GRO mRNA and, to a lesser degree, NAP-1 mRNA. Apparently, the irritation produced by SM directly or indirectly induces such epithelial cells to manufacture these growth factors. In the rabbit, hair follicles are known to be the main source of new epithelial cells after the covering epithelium has been destroyed. Therefore, GRO is probably a major autocrine-paracrine stimulus for such repair. A brief review of the role of cytokines in dermal inflammation is presented.

Functional heterogeneity among CD4+ T-cell clones from blood and skin lesions of leprosy patients. Identification of T-cell clones distinct from Th0, Th1 and Th2

In the present study we examined the functional properties of T-cell clones reactive with Mycobacterium leprae and other mycobacterial antigens. Clones isolated from the skin lesions and blood of leprosy patients across the spectrum were exclusively CD4+CD8- and expressed the alpha beta T-cell receptor. Substantial heterogeneity in the production of cytokines, in particular interleukin-4 (IL-4), was observed, although no striking correlation with clinical status was apparent. A variety of patterns of cytokine secretion distinct from those of T-helper type-1 (Th1) Th2 or Th0, as defined in murine studies, was evident. Most noteworthy was a large number of clones from skin which secreted neither IL-2 nor IL-4, but large amounts of tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma). Clones isolated from the blood of leprosy patients had a more restricted cytokine secretion profile, and appeared to resemble more closely previously described patterns, including those of high level production of IL-2 and/or IL-4. Virtually all clones, from either skin or blood, produced high levels of IFN-gamma, and thus many clones were IL-4 and IFN-gamma co-producers. The pattern of cytokine production by skin-derived T-cell clones was significantly affected by the in vitro activation status of the cells. Cells enriched in activated blasts tended to produce more IL-4 than small resting cells. In addition, the production of IFN-gamma by skin T-cell clones after < or = 10 weeks of culture was strikingly distinct from that of these clones after 5 months of culture. IL-4 and IFN-gamma co-producing clones shifted to a Th2-like pattern with much less IFN-gamma secretion, whereas non-IL-4-producing clones secreted much higher levels of IFN-gamma after prolonged culture, and became much more Th1-like. However, there was still no correlation between clinical status and pattern of cytokines produced. These results imply that a high fraction of T cells exists in leprosy lesions that is distinct from or that has not yet fully matured into Th1 or Th2 cells.

Tumour necrosis factor-alpha (TNF-alpha) synthesis is associated with the skin and peripheral nerve pathology of leprosy reversal reactions

Leprosy may be complicated by episodes of increased cell-mediated immunity towards Mycobacterium leprae (reversal reactions) which result in severe local immunopathology in skin lesions and peripheral nerves. Using in situ hybridization and MoAb techniques we have demonstrated TNF-alpha mRNA and TNF-alpha protein in macrophages infiltrating leprosy skin and peripheral nerve. Levels of TNF-alpha mRNA are significantly increased in reactional skin and nerve, particularly in borderline tuberculoid patients. TNF-alpha mRNA and TNF-alpha protein levels are higher in reactional nerves then reactional skin. In both reactional skin and nerve TNF-alpha mRNA is more abundant than TNF-alpha protein; this may reflect the rapid turnover of TNF-alpha protein in an immunologically dynamic situation, such as is seen in reversal reaction. Our findings emphasize the importance of documenting both mRNA and protein production when assessing the role of cytokines in pathology. The leprosy reversal reaction may be regarded as a useful model of tissue immunopathology in which TNF-alpha is generated as part of the host response to infection, but also produces local tissue damage.

T lymphocytes derived from skin lesions of patients with psoriasis vulgaris express a novel cytokine pattern that is distinct from that of T helper type 1 and T helper type 2 cells

In various immunological disorders the pathomechanisms of tissue damage are causally associated with specific patterns of locally produced cytokines. To study the molecular and cellular mechanisms involved in the manifestation of psoriasis vulgaris we have assessed the cytokine mRNA profile expressed in lesional psoriatic skin and in T cell clones (TCC) that were established from skin lesions of patients with psoriasis. As demonstrated by use of the polymerase chain reaction (PCR), psoriasis lesions consistently exhibit transcription of a complex pattern of cytokines. It includes mediators selectively produced by T lymphocytes [interferon (IFN)-gamma, tumor necrosis factor (TNF)-beta, interleukin (IL)-2, IL-3 and IL-5] as well as cytokines secreted by various cell types [transforming growth factor (TGF)-alpha/-beta, TNF-alpha, IL-6/-8 and granulocyte-macrophage-colony stimulating factor], while IL-4 is missing. With the exception of TGF-alpha, this cytokine profile was also observed in lesional psoriatic T cell clones yielding supernatants mitogenic for keratinocytes in vitro (MTCC), but not in T cell clones yielding supernatants that inhibited keratinocyte proliferation (STCC). The congruent cytokine expression of psoriatic skin lesions and MTCC emphasizes that inflammation in psoriasis is driven by a sofar unrecognized regulatory T cell subset that may serve to control epidermal regeneration and convey immunosurveillance over epithelial surfaces. It is characterized by the combined expression of IFN-gamma, TGF-beta, IL-2 and IL-5 in the absence of IL-4 and by its selective capacity to enhance keratinocyte proliferation. This newly defined combination of regulatory properties of a distinct T cell population cannot be reconciled with an immune response of the T helper cells (TH)0, TH1 or TH2 type.

Divergent T-cell cytokine patterns in inflammatory arthritis

A major immunoregulatory mechanism in inflammatory infections and allergic diseases is the control of the balance of cytokines secreted by Th1/Th2 subsets of T helper (Th) cells. This might also be true in autoimmune diseases; a Th2 pattern that prevents an effective immune response in infections with intracellular bacteria may favor immunosuppression in autoimmune disease. The pattern of cytokine expression was compared in the synovial tissue from patients with a typical autoimmune disease, rheumatoid arthritis, and with a disorder with similar synovial pathology but driven by persisting exogenous antigen, reactive arthritis. We screened 12 rheumatoid and 9 reactive arthritis synovial tissues by PCR and in situ hybridization for their expression of T-cell cytokines. The cytokine pattern differs significantly between the two diseases; rheumatoid arthritis samples express a Th1-like pattern whereas in reactive arthritis interferon gamma expression is accompanied by that of interleukin 4. Studying the expression of cytokines by in situ hybridization confirmed the results found by PCR; they also show an extremely low frequency of cytokine-transcribing cells. In a double-staining experiment, it was demonstrated that interleukin 4 is made by CD4 cells. These experiments favor the possibility of therapeutic intervention in inflammatory rheumatic disease by means of inhibitory cytokines.

Th1-Th2 paradigm: insights from leprosy

The mechanism by which T cells and cytokines regulate immune processes in skin can be investigated by studying patients with leprosy. The disease, caused by the obligate intracellular bacterium Mycobacterium leprae, forms a spectrum. At one pole, patients with tuberculoid leprosy are able to restrict the growth of the pathogen and their skin lesions are characterized by a predominance of CD4+ T cells and type 1 cytokines including interleukin 2 and interferon gamma. At the opposite pole, patients with lepromatous leprosy are unable to contain the infection and their skin lesions are characterized by a predominance of CD8+ T cells and type 2 cytokines including interleukins 4 and 10. A key determinant of the T-cell cytokine response may be interleukin 12, which selectively favors expansion of CD4+ T cells producing interferon gamma. By understanding the factors that regulate T-cell and cytokine responses in leprosy, it should be possible to devise specific immunologic interventions in diseases of skin.

Nerve and skin damage in leprosy is associated with increased intralesional heat shock protein

Leprosy is frequently complicated by the development of reversal reactions in which peripheral nerve and skin lesions become inflamed and irreversible nerve damage may ensue. Increased expression of proteins belonging to the 70-kD heat shock family (hsp 70) occurs in cells of the central nervous system exposed to hyperthermia, physical damage or drug-induced trauma. In the present study we have used immunocytochemical staining to monitor hsp70 levels in peripheral nerves infected by Mycobacterium leprae. Hsp70 was detected in skin and nerve lesions from all leprosy patients, but was particularly prominent in lesions from patients undergoing reversal reactions. Hsp70 immunocytochemistry can thus be used as a marker of neural injury in the peripheral as well as in the central nervous system. The cellular dynamics of nerve damage in leprosy are currently poorly understood, and we postulate that the immunopathology of leprosy may be partly due to an autoimmune response to heat shock proteins.

T cell receptor analysis in rheumatoid arthritis: what have we learnt?

Many clues point to a role for T lymphocytes in the pathogenesis of rheumatoid arthritis (RA), although the importance of these cells and their position within the rheumatoid pathogenic scheme remain unknown. Encouraged by data from animal models of T-lymphocyte-mediated autoimmunity, a major focus of research into the role of T lymphocytes in RA has been the usage of T cell receptor V genes in rheumatoid synovitis. Despite many methodologic problems, involving choice of patients and controls, choice of specimens, and technical factors, several conclusions can be drawn from the published research. In particular, synovial T lymphocyte populations, as a whole, frequently show biased V gene usage and restricted clonality within those T lymphocyte subsets that utilize over-represented V gene families. Continued research into these synovial T lymphocyte subsets should provide important insights into the pathogenesis of RA, particularly if solutions to the identified methodologic problems are implemented.

Mycobacteria induce CD4+ T cells that are cytotoxic and display Th1-like cytokine secretion profile: heterogeneity in cytotoxic activity and cytokine secretion levels

Protective immunity against mycobacteria is dependent on antigen-specific T cells. Current evidence suggests that not only helper T cells that activate infected macrophages but also cytotoxic T cells (CTL) that lyse infected macrophages are involved in protection. Mycobacterium-specific CD4+ CTL are readily detectable among primary peripheral T cells but what proportion of CD4+ T cells display cytotoxic activity is not known. Whether the cytotoxic CD4+ T cells are identical to or distinct from those that produce interferon (IFN)-gamma is also unknown. In addition, studies on CTL in mycobacterial infections have focused primarily on selected antigens like hsp65 but have not analyzed systematically whether other mycobacterial antigens can activate CTL as well. These issues are relevant not only to a further understanding of protective immunity and immunopathology but also may have implications for the design of effective vaccines. To start addressing these issues, we have studied a large panel of CD4+ T cell clones specific for a broad range of mycobacterial antigens, and analyzed their ability to lyse mycobacterium-pulsed target cells and to release IFN-gamma and interleukin (IL)-4. Our results show that the vast majority of CD4+ T cell clones are able to lyse mycobacterial antigen-pulsed target cells, and that those CTL can be triggered by a wide variety of mycobacterial antigens. CD4+ CTL released high levels of IFN-gamma, but low or nondetectable levels of IL-4. In contrast, control tetanus toxoid-specific T cell clones or lines displayed poor or weak cytotoxic activity and released high levels of IL-4. The antimycobacterial clones appeared to be heterogeneous in their levels of cytotoxic activity and IFN-gamma release. Interestingly one T cell clone was able to lyse only mycobacterium-pulsed macrophages but not B cells suggesting possible selectivity in target cell recognition for some CTL. These in vitro data have to be interpreted with some caution. Nevertheless they confirm and significantly extend previous observations and suggest that mycobacteria preferentially induce CD4+ T helper type 1 (Th1)-like cells that display cytotoxic activity, and release high levels of IFN-gamma but no or little IL-4. The induction of such Th1 like cells is specific for mycobacteria since tetanus toxoid induced T cells that were poorly or not cytolytic and secreted high levels of IL-4.

Immunology of leprosy

The host immune response to Mycobacterium leprae is critical for control of the infection but also responsible for the immunopathological damage to skin and nerves. The complex and varied immune responses to the organism are the basis for the clinical spectrum of disease ranging from tuberculoid to lepromatous leprosy. The cellular interactions underlying this spectrum are discussed and the antigenic components of the bacillus briefly reviewed. M. leprae has evolved a variety of mechanisms to avoid macrophage bactericidal mechanisms. These result in the persistence of bacilli and the release of cytokines leading to chronic granulomatous inflammation. The immune response to M. leprae is dynamic and spontaneous variations in cellular reactivity occur with time leading to type I and II leprosy reactions. The factors which preset the host immune response to a tuberculoid or lepromatous pattern and which precipitate reactional episodes remain to be elucidated.

Cytokine production at the site of disease in human tuberculosis

Clinical and immunologic evidence suggests that tuberculous pleuritis provides a model to understand protective immune mechanisms against Mycobacterium tuberculosis. We therefore evaluated the pattern of cytokine mRNA expression and cytokine production in pleural fluid and blood of patients with tuberculous pleuritis. RNA was extracted from mononuclear cells, reverse transcribed to cDNA, and amplified by polymerase chain reaction (PCR). After normalization for T-cell cDNA, cDNA from pleural fluid cells and peripheral blood mononuclear cells (PBMC) was amplified with cytokine-specific primers. PCR product was quantified by Southern blot. For the Th1 cytokines gamma interferon (IFN-gamma) and interleukin-2 (IL-2), PCR product was greater in pleural fluid than in blood, whereas PCR product for the Th2 cytokine IL-4 was decreased in pleural fluid compared with blood. Concentrations of IFN-gamma were elevated in pleural fluid compared with serum, but IL-2, IL-4, and IL-5 were not detectable. Mean concentrations of IFN-gamma and IL-2 in supernatants of M. tuberculosis-stimulated pleural fluid cells were significantly greater than corresponding concentrations in supernatants of stimulated PBMC. In situ hybridization showed that increased IFN-gamma production by pleural fluid cells was associated with a 20- to 60-fold increase in the frequency of antigen-reactive IFN-gamma-mRNA-expressing cells. Because IL-10 can be produced by T cells and macrophages, pleural fluid cells and PBMC were normalized for beta-actin cDNA content and then amplified by PCR with IL-10-specific primers. IL-10 mRNA was greater in pleural fluid cells than in PBMC and was expressed predominantly by macrophages. IL-10 concentrations were elevated in pleural fluid versus serum. These data provide strong evidence for compartmentalization of Th1 cytokines and IL-10 at the site of disease in humans with a resistant immune response to mycobacterial infection.

Cytokine patterns in the pathogenesis of human leishmaniasis

The host response to infection appears to be regulated by specific patterns of local cytokine production. In the mouse, resistance to many pathogens including Leishmania is associated with a TH1 cytokine profile, IL-2 and IFN-gamma; whereas susceptibility to infection is associated with production of TH2 cytokines, IL-4, IL-5, and IL-10. To determine the cytokine patterns of the local immune response to Leishmania infection in humans, we used the polymerase chain reaction to compare cytokine mRNAs in biopsy specimens of American cutaneous leishmaniasis. In localized cutaneous leishmaniasis and the Montenegro delayed-type hypersensitivity reaction, type 1 cytokine mRNAs such as IL-2, IFN-gamma, and lymphotoxin were relatively predominant. In the chronic and destructive mucocutaneous form of leishmaniasis, there was a mixture of type 1 and type 2 cytokines, with a striking abundance of IL-4 mRNA in lesions. These results suggest that clinical course of infection with Leishmania braziliensis in man is associated with specific local patterns of cytokine production.