Mycobacterial catalase-peroxidase is a tissue antigen and target of the adaptive immune response in systemic sarcoidosis

Mycobacterial ESAT-6 and katG are recognized by sarcoidosis CD4+ T cells when presented by the American sarcoidosis susceptibility allele, DRB1*1101

INTRODUCTION

Genetic associations of American sarcoidosis susceptibility implicate MHC class II allele, DRB1*1101. We previously reported immune recognition of Mycobacterium peptides from peripheral cells of 26 sarcoidosis subjects, 24 PPD- healthy volunteers, and eight with latent tuberculosis infection.

MATERIALS AND METHODS

In order to further link these genetic and immunologic pillars of sarcoidosis pathogenesis, we performed flow cytometry on these same subjects to identify the cells responsible for immune responses to ESAT-6 and katG peptides, followed by HLA typing to determine allelic associations with recognition.

DISCUSSION AND CONCLUSION

Sarcoidosis CD4+ T cells were primarily responsible for the systemic responses. Recognition was inhibited by monoclonal antibody against HLA-DR and HLA-DQ, but not HLA-DP. Immune recognition of ESAT-6 peptide NNALQNLARTISEAG was associated with possession of DRB1*1101. ESAT-6 and katG presented by antigen-presenting cells expressing DRB1*1101-induced Th-1 responses from sarcoidosis T cells, thus providing a mechanistic insight for the association of HLA DRB1*1101 with sarcoidosis, and sarcoidosis T cell interaction with microbial antigens.

Hypothesis: sarcoidosis is a STAT1-mediated disease

Immunologic pathways involved in sarcoidosis pathogenesis are largely unknown. We hypothesized that patients with sarcoidosis have characteristic mRNA profiles. Microarray analysis of gene expression was done on peripheral blood (12 patients, 12 controls), lung (6 patients, 6 controls) and lymph node (8 patients, 5 controls). Comparing peripheral blood from patients with sarcoidosis to controls, 872 transcripts were upregulated and 1039 were downregulated at >1.5-fold change and a significant q value. Several transcripts associated with interferon and STAT1 were upregulated. Lung and lymph node analyses also showed dramatic increases in STAT1 and STAT1-regulated chemokines. Granulomas in lymph nodes of patients with sarcoidosis expressed abundant STAT1 and phosphorylated STAT1. STAT1 might play an important role in sarcoidosis. This novel hypothesis unites seemingly disparate observations with regard to sarcoidosis including implication of a casual role for interferons, a suspected infectious trigger, T(H)1 predominating lymphocytes in bronchoalveolar lavage, and the association with hypercalcemia.

T helper type 2 differentiation is associated with induction of antibacterial defense mechanisms in blood lymphocytes of patients with sarcoidosis

Whereas sarcoidosis is characterized by an excessive inflammatory immune response mainly at the pulmonary site, circulating T lymphocytes poorly respond to antigen challenge. It has been suggested, that the extensive local inflammation might be triggered by bacterial pathogens. Recently, it has been shown that this paradoxically immunological situation likely results from a disequilibrium between effector and regulatory T lymphocytes (T(reg)). Here, we apply a DNA microarray approach in order to analyze circulating T cells for specific dysregulatory events, which should provide detailed insights in the impairment of cell-mediated immunity. Gene expression profiles were performed from peripheral blood T lymphocytes of untreated patients with pulmonary sarcoidosis (stage I) (n = 3) and a control group consisting of healthy donors (n = 3). Circulating T lymphocytes in sarcoidosis exhibit a specific gene expression pattern of molecules that are primarily involved in immune responses and lymphocyte signalling. Compared to controls patients with sarcoidosis display also alterations in gene expression of molecules with bacteriolytic and chemotactic function. Among others, array analysis resulted in increased transcript levels of Th2 immune response, whereas genes coding for molecules involved in Th1 differentiation are down-regulated. Furthermore, genes encoding proteins representing primordial antimicrobial peptides which may mobilise immunocompetent T cells and other inflammatory cells are up-regulated. This observation supports recent reports suggesting that bacterial antigens play a role in the pathogenesis of sarcoidosis. However, the results of our study indicate an unbalanced immune response towards Th2 in the peripheral blood of patients with sarcoidosis.

T cell responses to mycobacterial catalase-peroxidase profile a pathogenic antigen in systemic sarcoidosis

Sarcoidosis is a systemic granulomatous disease associated with local epithelioid granulomas, CD4(+) T cells, and Th1 cytokines. The tissue Ags that drive this granulomatous inflammation are uncertain. In this study, we used IFN-gamma-ELISPOT assays and flow cytometry to assess lung and blood T cell responses to the candidate pathogenic Ag, Mycobacterium tuberculosis catalase-peroxidase (mKatG) in patients with sarcoidosis from two centers. Despite differences in patient phenotypic, genetic, and prognostic characteristics, we report that T cell responses to mKatG were remarkably similar in these cohorts, with higher frequencies of mKatG-reactive, IFN-gamma-expressing T cells in the blood of sarcoidosis patients compared with nontuberculosis sensitized healthy controls, and (in a subset) in greater numbers than T cells reactive to purified protein derivative. In sarcoidosis, mKatG-reactive CD4(+) Th1 cells preferentially accumulated in the lung, indicating a compartmentalized response. Patients with or without Löfgren syndrome had similar frequencies of mKatG specific IFN-gamma-expressing blood T cells. Circulating mKatG-reactive T cells were found in chronic active sarcoidosis but not in patients with inactive disease. Together, these results demonstrate that T cell responses to mKatG in sarcoidosis fit a profile expected for a pathogenic Ag, supporting an immunotherapeutic approach to this disease.

Childhood sarcoidosis: A rare but fascinating disorder

Childhood sarcoidosis is a rare multisystemic granulomatous disorder of unknown etiology. In the pediatric series reported from the southeastern United States, sarcoidosis had a higher incidence among African Americans. Most reported childhood cases have occurred in patients aged 13-15 years. Macrophages bearing an increased expression of major histocompatibility class (MHC) II molecules most likely initiate the inflammatory response of sarcoidosis by presenting an unidentified antigen to CD4+ Th (helper-inducer) lymphocytes. A persistent, poorly degradable antigen driven cell-mediated immune response leads to a cytokine cascade, to granuloma formation, and eventually to fibrosis. Frequently observed immunologic features include depression of cutaneous delayed-type hypersensitivity and a heightened helper T cell type 1 (Th1) immune response at sites of disease. Circulating immune complexes, along with signs of B cell hyperactivity, may also be found. The clinical presentation can vary greatly depending upon the organs involved and age of the patient. Two distinct forms of sarcoidosis exist in children. Older children usually present with a multisystem disease similar to the adult manifestations, with frequent hilar lymphadenopathy and pulmonary infiltrations. Early-onset sarcoidosis is a unique form of the disease characterized by the triad of rash, uveitis, and arthritis in children presenting before four years of age. The diagnosis of sarcoidosis is confirmed by demonstrating a typical noncaseating granuloma on a biopsy specimen. Other granulmatous diseases should be reasonably excluded. The current therapy of choice for sarcoidosis in children with multisystem involvement is oral corticosteroids. Methotrexate given orally in low doses has been effective, safe and steroid sparing in some patients. Alternative immunosuppressive agents, such as azathioprine, cyclophosphamide, chlorambucil, and cyclosporine, have been tried in adult cases of sarcoidosis with questionable efficacy. The high toxicity profile of these agents, including an increased risk of lymphoproliferative disorders and carcinomas, has limited their use to patients with severe disease refractory to other agents. Successful steroid sparing treatment with mycophenolate mofetil was described in an adolescent with renal-limited sarcoidosis complicated by renal failure. Novel treatment strategies for sarcoidosis have been developed including the use of TNF-alpha inhibitors, such as infliximab. The long-term course and prognosis is not well established in childhood sarcoidosis, but it appears to be poorer in early-onset disease.

The immunology of sarcoidosis

Sarcoidosis continues to be a disease of research interest because of its complicated immune mechanisms and elusive etiology. So far, it has been established that granulomatous inflammation in sarcoidosis is predominantly a T-helper 1 immune response mediated by a complex network of lymphocytes, macrophages, and cytokines. The cause of progression to a chronic and potentially fibrotic form is unclear but may involve loss of apoptotic mechanisms, loss of regulatory response, or a persistent antigen that cannot be cleared. Recent genomic and proteomic technology has emphasized the importance of host susceptibility and gene-environment interaction in the expression of the disease.

Higher monocyte expression of TLR2 and TLR4, and enhanced pro-inflammatory synergy of TLR2 with NOD2 stimulation in sarcoidosis

INTRODUCTION

Sarcoidosis is an inflammatory disease of unknown etiology. However, an infectious cause has been proposed suggesting a role for pattern-recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding domain, leucin-rich repeat containing family proteins (NLRs), in the pathogenesis.

OBJECTIVE

Our aim was to investigate whether differences in TLR2 and TLR4 expression, and the response to TLR2, TLR4, and NOD2 stimulation, are associated with sarcoidosis.

MATERIALS AND METHODS

Blood mononuclear cells from sarcoidosis patients (n = 24) and healthy subjects (n = 19) were incubated with the TLR2 ligands PGN and Pam3CSK4, the TLR4 ligand LPS, the NOD2 ligand MDP, or medium alone. After 16 h, monocyte TLR2 and TLR4 expression and cytokine secretion, including TNFalpha, IL-1 beta, IL-6, IL-8, IL-10, and IL-12p70, were measured using flow cytometry and cytometric bead array.

RESULTS

TLR2 and TLR4 expression at baseline was significantly higher in patients. Combined TLR2 and NOD2 stimulation induced a four-fold higher secretion of TNFalpha and a 13-fold higher secretion of IL-1 beta in patients. Additionally, there was a synergistic effect of TLR2 with NOD2 stimulation on induction of IL-1 beta in patients, whereas IL-10 was synergistically induced in healthy subjects.

CONCLUSION

Increased TLR expression and enhanced secretion of pro-inflammatory cytokines after combined TLR2 and NOD2 stimulation may be related to the pathogenesis of sarcoidosis.

Superoxide dismutase A antigens derived from molecular analysis of sarcoidosis granulomas elicit systemic Th-1 immune responses

BACKGROUND

Sarcoidosis is an idiopathic granulomatous disease with pathologic and immunologic features similar to tuberculosis. Routine histologic staining and culture fail to identify infectious agents. An alternative means for investigating a role of infectious agents in human pathogenesis involves molecular analysis of pathologic tissues for microbial nucleic acids, as well as recognition of microbial antigens by the host immune system. Molecular analysis for superoxide dismutase A (sodA) allows speciation of mycobacteria. SodA is an abundantly secreted virulence factor that generates cellular immune responses in infected hosts. The purpose of this study is to investigate if target antigens of the sarcoidosis immune response can be identified by molecular analysis of sarcoidosis granulomas.

METHODS

We detected sodA amplicons in 12 of 17 sarcoidosis specimens, compared to 2 of 16 controls (p = 0.001, two-tailed Fisher's exact test), and 3 of 3 tuberculosis specimens (p = 0.54). Analysis of the amplicons revealed sequences identical to M. tuberculosis (MTB) complex, as well as sequences which were genetically divergent. Using peripheral blood mononuclear cells (PBMC) from 12 of the 17 sarcoidosis subjects, we performed enzyme-linked immunospot assay (ELISPOT) to assess for immune recognition of MTB sodA peptides, along with PBMC from 26 PPD- healthy volunteers, and 11 latent tuberculosis subjects.

RESULTS

Six of 12 sarcoidosis subjects recognized the sodA peptides, compared to one of 26 PPD- controls (p = 0.002), and 6/11 PPD+ subjects (p = .68). Overall, 10 of the 12 sarcoidosis subjects from whom we obtained PBMC and archival tissue possessed molecular or immunologic evidence for sodA.

CONCLUSION

Dual molecular and immunologic analysis increases the ability to find infectious antigens. The detection of Th-1 immune responses to sodA peptides derived from molecular analysis of sarcoidosis granulomas reveals that these are among the target antigens contributing to sarcoidosis granulomatous inflammation.

Microbial antigen treatment in sarcoidosis – A new paradigm?

Increasing evidence suggests that the risk for sarcoidosis is related to exposure to microbes, particularly molds. Microbial cell wall agents, even in the absence of clinical infection, could cause a late hypersensitivity reaction leading to the formation of granulomas. A few interventions studies using antimicrobial treatment demonstrate improvement in sarcoidosis. It is suggested that diagnostic tools for the presence of microbes are used in patients with sarcoidosis and that antimicrobial treatment is considered in cases resistant to corticosteroids.

Multiple Mycobacterium antigens induce interferon-gamma production from sarcoidosis peripheral blood mononuclear cells

Studies of sarcoidosis immunology have noted oligoclonal T cell populations, suggesting cell-mediated immunity that is antigen-specific. Sarcoidosis immunology and pathology are most similar to mycobacterial infections. Mycobacterium tuberculosis infection in mice and humans reflects T helper 1 (Th1) immune responses to multiple cell wall and secreted antigens. We investigated if the oligoclonal immune response in individual sarcoidosis subjects could be elicited by multiple secreted mycobacterial antigens by performing ex vivo enzyme-linked immunospot assay (ELISPOT) on peripheral blood mononuclear cells (PBMC) from 30 sarcoidosis, 26 purified protein derivative negative (PPD-) control and 10 latent tuberculosis subjects (PPD+) to assess Th1 responses to mycobacterial superoxide dismutase A (sodA), catalase-peroxidase (katG) and early secreted antigenic target protein (ESAT-6). A significant difference was noted among the sarcoidosis and PPD- control subjects to ESAT-6 [12 of 30 versus one of 26 (P = 0.0014)], katG [nine of 30 versus none of 26 (P = 0.002)] and sodA [12 of 30 versus none of 26 (P = 0.002)]. There was no significant difference between sarcoidosis and PPD+ subjects. Twelve sarcoidosis subjects recognized two or more mycobacterial proteins, as well as multiple distinct epitopes within individual proteins. One sarcoidosis subject on whom we collected bronchoalveolar lavage (BAL) fluid and PBMC had no recognition of mycobacterial antigens using PBMC, but BAL fluid demonstrated strong Th1 immune responses to ESAT-6 and katG. Individual sarcoidosis subjects recognized not only multiple mycobacterial proteins, but multiple distinct peptides within a specific protein, thus demonstrating that multiple mycobacterial epitopes elicit the Th1 immune response observed. Immune responses by sarcoidosis T cells to mycobacterial proteins may have an important role in sarcoidosis pathogenesis.

Role of CD4+ T cells in sarcoidosis

Activated pulmonary CD4(+) T lymphocytes of the Th-1 type are essential for the inflammatory process in sarcoidosis, and IFN-gamma production is crucial for the characteristic granuloma formation. Both the T cells and their inflammatory mediators may constitute possible targets for immunotherapy. A particular T-cell subset, the T-cell receptor (TCR) AV2S3(+) bronchoalveolar lavage (BAL) CD4(+) T cells, is found at dramatically increased levels in the BAL fluid of human leukocyte antigen (HLA)-DRB1*0301-positive and/or HLA-DRB3*0101-positive patients with sarcoidosis. The AV2S3(+) BAL CD4(+) T cells strongly associate with the sarcoid inflammation, and future studies on this particular T-cell subset to reveal their specificity may lead to the identification of sarcoidosis-specific antigen(s). T-cell subpopulations with regulatory functions (i.e., natural killer T cells and T regulatory cells) have recently been described as abnormal in sarcoidosis. Dysfunctional regulatory T cells may allow T effector cells to contribute to the formation of granulomas, and they may thus be relevant for the inflammatory process in this disease. These findings are exciting news and will be of help in designing new treatment strategies.

Potential etiologic agents in sarcoidosis

The etiology of sarcoidosis remains uncertain. The hallmark of sarcoidosis is the epithelioid granuloma, which serves as a necessary starting point for considering disease etiology. Any etiologic agent of sarcoidosis must also explain the typical clinical behaviors and characteristic immunopathologic features of the disease. One clinical observation that serves as a bridge to the etiology of sarcoidosis is the Kveim reaction. In this reaction, local epithelioid granulomas develop several weeks after the intradermal injection of homogenates of sarcoidosis tissue. Our group capitalized on the known properties of the Kveim reagent to search for candidate pathogenic tissue antigens in sarcoidosis without other a priori hypotheses regarding possible microbial or autoimmune etiologies. Using a limited proteomics approach based on the physicochemical properties of Kveim reagent, we detected a limited number of poorly soluble antigenic proteins in sarcoidosis tissues by protein immunoblotting, using sarcoidosis sera. Matrix-associated laser desorption/ionization-time of flight mass spectrometry identified one of these antigens to be the Mycobacterium tuberculosis catalase-peroxidase protein (mKatG). We found IgG responses to recombinant mKatG in more than 50% of patients with sarcoidosis but rarely in purified protein derivative (PPD)-negative control subjects. These findings support the conclusion that mKatG is a tissue antigen and target of the adaptive immune response in sarcoidosis, providing further evidence of a mycobacterial etiology in a subset of sarcoidosis. More generally, the approach used in these studies might be employed to discover and validate other candidate pathogenic antigens in sarcoidosis or other granulomatous disorders.

HLA class II amino acid epitopes as susceptibility markers of sarcoidosis

Sarcoidosis is a multisystemic disorder of unknown etiology, affecting primarily the lung and characterized by epithelioid granulomas. Disease association studies showed human leukocyte antigen (HLA) class II to be related to sarcoidosis. Initially, we studied the association of sarcoidosis with DQB1, and in the present study, we evaluated all amino acid variants of the HLA-DPB1, -DQB1, -DRB1, -DRB3, -DRB4 and -DRB5 genes to identify possible polymorphisms associated with the disease. Patients and controls were typed for class II genes to the allele level by sequence-based typing. Multiple logistic regression models showed DRAla71 and DQPhe9 to be independently associated with the disease. Subdivision of patients according to their radiographic stage resulted in identification of DRArg74 as independent associated residue in the RS I group, whereas DRAla71 and DQTyr30 were associated with RS II-IV groups. Polymorphic residues specifically associated with sarcoidosis shed new light on the characteristics of sarcoidosis-triggered peptides. Overall, pocket 9 of DQ and pocket 4 of DR seem to be the most important areas involved in the association with sarcoidosis.

Considering an infectious etiology of sarcoidosis

Sarcoidosis is a systemic granulomatous disease of unknown cause. An infectious etiology of sarcoidosis has long been suspected, but only recently has scientific evidence provided a strong link between infectious agents and sarcoidosis. Moreover, recent advances in our understanding of the relationships between sarcoidosis phenotype and host genetic factors may further illuminate the mechanisms linking infection and sarcoidosis.

Gene-environment interactions in sarcoidosis: challenge and opportunity

Susceptibility to most human diseases is polygenic, with complex interactions between functional polymorphisms of single genes governing disease incidence, phenotype, or both. In this context, the contribution of any discrete gene is generally modest for a single individual, but may confer substantial attributable risk on a population level. Environmental exposure can modify the effects of a polymorphism, either by providing a necessary substrate for development of human disease or because the effects of a given exposure modulate the effects of the gene. In several diseases, genetic polymorphisms have been shown to be context dependent, ie, the effects of a genetic variant are realized only in the setting of a relevant exposure. Because sarcoidosis susceptibility is dependent on both genetic and environmental modifiers, the study of gene-environment interactions may yield important pathogenetic information and will likely be crucial for uncovering the range of genetic susceptibility loci. The complexity of these relationships implies, however, that investigations of gene-environment interactions will require the study of large cohorts with carefully defined exposures and similar clinical phenotypes. A general principle is that the study of gene-environment interactions requires a sample size at least severalfold greater than for either factor alone. To date, the presence of environmental modifiers has been demonstrated for one sarcoidosis susceptibility locus, HLA-DQB1, in African-American families. This article reviews general considerations obtaining for the study of gene-environment interactions in sarcoidosis. It also describes the limited current understanding of the role of environmental influences on sarcoidosis susceptibility genes.

[Epidemiology of sarcoidosis]

La sarcoidosis es una enfermedad multisistémica que afecta frecuentemente al pulmón. Su incidencia y prevalencia han sido ampliamente estudiadas, pero la falta de estandarización del diagnóstico, los diferentes métodos de detección de casos y la escasa sensibilidad y especificidad de las pruebas diagnósticas explican los datos discordantes. El pronóstico es generalmente favorable. Gran parte de las personas afectadas no manifestarán nunca síntomas y muchas tienen remisión espontánea. El curso es crónico en el 10-30% de los casos, con un deterioro permanente de la función pulmonar. La enfermedad es el resultado de la acción de un agente externo que desencadena la respuesta inmunitaria característica en individuos genéticamente susceptibles. Se han implicado factores ambientales, ocupacionales y genéticos, pero las investigaciones están todavía en los inicios. Estudios de casos y controles, así como los avances en biología molecular, ayudarán a definir los factores de susceptibilidad genética y a entender los distintos fenotipos de la sarcoidosis.

Mycobacterium tuberculosis Antigen 85A induces Th-1 immune responses in systemic sarcoidosis

Sarcoidosis is a granulomatous disease of unknown etiology, characterized by a Th-1 immunophenotype. Although humoral immune responses by sarcoidosis subjects to mycobacterial proteins have been detected, mycobacterial antigens capable of inducing cellular immune responses in sarcoidosis subjects have not been reported. We used the enzyme-linked immunospot assay to assess for recognition of the Mycobacterium tuberculosis mycolyl transferase, Antigen 85A, by peripheral blood mononuclear cells from 25 sarcoidosis subjects, 22 PPD- (purified protein derivative) healthy volunteers, and 16 PPD+ healthy subjects. Reactivity to Ag85A whole protein was observed in 15 of 25 sarcoidosis subjects compared to 2 of 22 PPD- subjects (p=0.0006, Fisher's exact test) and to 14 of 16 PPD+ subjects (p=0.084, Fisher's exact test). Monoclonal antibody against HLA-DR inhibited recognition. In addition to immune recognition of Ag85A whole protein, peptide-mapping studies identified four immunogenic Ag85A peptides, which induced Th-1 immune responses in individual sarcoidosis subjects, suggesting that multiple epitopes from a mycobacterial protein may have a role in sarcoidosis immunopathogenesis.

Linkage between Toll-like receptor (TLR) 2 promotor and intron polymorphisms: functional effects and relevance to sarcoidosis

The intracellular pathogens Propionibacterium acnes and Mycobacterium tuberculosis have been leading suspects as the cause of sarcoidosis, a systemic disorder characterized by the formation of non-caseating granulomas. Toll-like receptor (TLR) 2 is important in the innate immune response against both pathogens, and is therefore of interest in sarcoidosis research. In the present study, three single nucleotide polymorphisms and one dinucleotide repeat polymorphism in the TLR-2 gene were genotyped in 419 sarcoidosis patients, divided into a study cohort and a validation cohort, and 196 healthy controls. In the study cohort we found a significant increase in prevalence of the AA-genotype at promotor location -16934 in patients with chronic disease compared to patients with acute/self-remitting sarcoidosis (34.5% versus 15.9%, respectively, P = 0.006, P(c) = 0.019). These results could not be confirmed in our validation cohort, implicating a possible role for TLR-2 genetics in only a small percentage of sarcoidosis patients. Furthermore, linkage was found between the promotor polymorphism -16934 A/T and the number of GT repeats in intron 1 (P < 0.0001). After in vitro stimulation of peripheral blood mononuclear cells (PMBCs) with different TLR-2 agonists, a correlation between induction of TNF-alpha (P = 0.008), interleukin (IL)-12 (P = 0.008) as well as IL-6 (P = 0.02), and the number of GT repeats was observed. In conclusion, the data show that polymorphisms in TLR-2 might be important in a small group of sarcoidosis patients and that their functional consequences explain partly some of the variance in cytokine pattern observed in different clinical phenotypes of this disease.

Immunopathogenesis of sarcoidosis

The immunopathogenesis of sarcoidosis has been difficult to charaterize given the heterogeneity of disease, the elusiveness of the causative antigen, and the lack of an adequate animal model. However, by examining well-defined clinical cohorts, the interplay between genetic predisposition and immunologic response has been increasingly informative. Technological advances in cellular analysis have allowed researchers to characterize the immune responses important in the maintenance of granulomatous inflammation. Finally, "new" clinical observations such as granuloma responsiveness to targeted biological therapies, sarcoid developing during immune restoration, and the relationship between sarcoidosis and Hepatitis C will provide future insight to the immunopathogenesis of sarcoidosis.

Potential biomarkers for diagnosis of sarcoidosis using proteomics in serum

BACKGROUND

Sarcoidosis is a multi-systemic inflammatory disorder, which affects the lungs in 90% of the cases. The main pathologic feature is chronic inflammation resulting in non-caseating granuloma formation. Until now there is no satisfying biomarker for diagnosis or prognosis of sarcoidosis. This study is focused on the detection of potential biomarkers in serum for the diagnosis of sarcoidosis using surface-enhanced laser desorption ionization-time of flight-mass spectrometry (SELDI-TOF-MS).

METHODS

For detection of potential biomarkers, protein profiles of anion exchange fractionated serum of 35 sarcoidosis patients and 35 healthy controls were compared using SELDI-TOF-MS. Sensitivities and specificities of the potential biomarkers obtained with SELDI-TOF-MS, generated with decision tree algorithm, were compared to the conventional markers angiotensin converting enzyme (ACE) and soluble interleukin-2 receptor (sIL-2R).

RESULTS

Optimal classification was achieved with metal affinity binding arrays. A single marker with a mass-to-charge (m/z) value of 11,955 resulted in a sensitivity and specificity of 86% and 63%, respectively. A multimarker approach of two peaks, m/z values of 11,734 and 17,377, resulted in a sensitivity and specificity of 74% and 71%, respectively. These sensitivities and specificities were higher compared to measurements of ACE and sIL-2R. Identification of the peak at m/z 17,377 resulted in the alpha-2chain of haptoglobin.

CONCLUSIONS

This study acts as a proof-of-principle for the use of SELDI-TOF-MS in the detection of new biomarkers for sarcoidosis. The peak of the multimarker at m/z 17,377 was identified as the alpha-2chain of haptoglobin.

Expression profiling in granulomatous lung disease

Granulomatous lung diseases, such as sarcoidosis, hypersensitivity pneumonitis, Wegener's granulomatosis, and chronic beryllium disease, along with granulomatous diseases of known infectious etiologies, such as tuberculosis, are major causes of morbidity and mortality throughout the world. Clinical manifestations of these diseases are highly heterogeneous, and the determinants of disease susceptibility and clinical course (e.g., resolution vs. chronic, progressive fibrosis) are largely unknown. The underlying pathogenic mechanisms of these diseases also remain poorly understood. Within this context, these diseases have been approached using genomic and proteomic technologies to allow us to identify patterns of gene/protein expression that track with clinical disease or to identify new pathways involved in disease pathogenesis. The results from these initial studies highlight the potential for these "-omics" approaches to reveal novel insights into the pathogenesis of granulomatous lung disease and provide new tools to improve diagnosis, clinical classification, course prediction, and response to therapy. Realizing this potential will require collaboration among multidisciplinary groups with expertise in the respective technologies, bioinformatics, and clinical medicine for these complex diseases.

[Epidemiology of sarcoidosis]

Sarcoidosis is a multisystemic disease in which lung involvement is common. Its incidence and prevalence have been extensively studied, but with contradictory results because of the lack of standard diagnostic criteria, variations in the methods for detecting cases, and the low sensitivity and specificity of diagnostic tests. Prognosis is generally favorable. Many of those affected remain asymptomatic and remission often occurs spontaneously, although between 10% and 30% of the patients have chronic disease and permanent deterioration in lung function. Sarcoidosis is caused by an external agent that triggers a characteristic immune response in genetically susceptible individuals. Environmental, occupational, and genetic factors have all been implicated, but research is still in the early stages. Case-control studies, as well as advances in molecular biology, will help to identify genetic susceptibility factors and to understand the different phenotypes of sarcoidosis.

Mycobacterial antigens may be important in sarcoidosis pathogenesis

PURPOSE OF REVIEW

To describe the most recent epidemiologic, molecular and immunologic literature related to the role of infectious antigens in sarcoidosis pathogenesis, with a focus upon Mycobacterium and Proprionibacterium species.

RECENT FINDINGS

Recent studies of successful molecular analysis for and humoral immunity to mycobacterial antigens from sarcoidosis patients have renewed interest in a potential role of mycobacteria in sarcoidosis. One study provided molecular and immunologic evidence for mycobacteria among sarcoidosis subjects from the United States. These studies, while preliminary, provide the groundwork for more in-depth studies of the potential role of mycobacteria in sarcoidosis pathogenesis. Proprionibacteria have also been proposed as a cause of sarcoidosis; a study of the detection of Proprionibacterium species nucleic acids throughout the lung of sarcoidosis and control subjects, however, suggests that these organisms are less likely to be causal.

SUMMARY

While the studies to date do not fulfill Koch's postulates, they do add further support to the hypothesis that infectious antigens, particularly those from mycobacteria, may have a causal role in some sarcoidosis cases. In future studies that purport to show an association of microbial antigen(s) with sarcoidosis, investigation of genetic risk factors contributing to risk will be important, in order to explain why some patients are found to have an association with microbial antigens and others are not.

Cellular recognition of Mycobacterium tuberculosis ESAT-6 and KatG peptides in systemic sarcoidosis

Sarcoidosis is an enigmatic disease with a pathology similar to that of tuberculosis. We detected Th-1 immune responses to Mycobacterium tuberculosis ESAT-6 and KatG peptides from peripheral blood mononuclear cells from 15/26 sarcoidosis, 1/24 purified-protein-derivative-negative (PPD-) (P < 0.0001, Fisher's exact test), and 7/8 PPD-positive (PPD+) subjects (P = 0.21). This finding provides immunologic links between mycobacteria and systemic sarcoidosis.

Transformation of pulmonary histoplasmosis to sarcoidosis: a case report

Histoplasmosis, a dimorphic fungus, and sarcoidosis, a disease of unknown etiology, share many clinical features, including typical manifestations of granulomatous inflammation involving the lungs and mediastinal lymphatics in association with constitutional symptoms. As such, they are often difficult to distinguish based upon clinical presentation. Recent studies suggest that sarcoidosis may be triggered by infectious agents. Here we present a case of documented pulmonary histoplasmosis that evolved into sarcoidosis. This case supports the notion that infections promote sarcoidosis in predisposed hosts.

The immune paradox of sarcoidosis and regulatory T cells

Sarcoidosis is characterized by extensive local inflammation (granuloma, cytokine secretion) associated with anergy (poor response to antigens in vitro and in vivo). We postulated that this paradoxical situation would correspond to a disequilibrium between effector and regulatory T lymphocytes (T reg cells). We show that CD4⁺CD25^brightFoxP3⁺ cells accumulate at the periphery of sarcoid granulomas, in bronchoalveolar lavage fluid, and in peripheral blood of patients with active disease. These cells exhibited powerful antiproliferative activity, yet did not completely inhibit TNF-α production. Sarcoidosis is therefore associated with a global T reg cell subset amplification whose activity would be insufficient to control local inflammation. At the same time, peripheral T reg cells exert powerful antiproliferative activity that may account for the state of anergy. Altogether, these findings advance our conceptual understanding of immune regulation in a way that resolves the immune paradox of sarcoidosis and permit us to envisage a profound clinical impact of T reg cell manipulation on immunity.

Endotoxin Up-regulates Interleukin-18

RATIONALE AND OBJECTIVES

Sarcoidosis is a granulomatous disease of unknown etiology characterized by a helper T-cell type 1-mediated process. Previously we demonstrated a role for interleukin-18 in sarcoidosis. Here we examine the regulation of interleukin-18 in this condition.

METHODS

Cytokine levels in sarcoid epithelial lining fluid were measured by ELISA. We examined interleukin-18 promoter activity and mRNA and protein levels in the epithelial lining fluid of individuals with active sarcoidosis, and of individuals recovered from sarcoidosis, in response to purified protein derivative of Mycobacterium tuberculosis, beryllium sulfate, zirconium sulfate, aluminum sulfate, and lipopolysaccharide. Endotoxin levels in the epithelial lining fluid of individuals with sarcoidosis, individuals recovered from sarcoidosis, and control subjects were assessed by Limulus amebocyte lysate analysis. Allele-specific polymerase chain reaction was used to genotype 94 patients with sarcoidosis and 97 control subjects for the interleukin-18 -607(A/C) polymorphism. Species-specific polymerase chain reaction identified bacterial DNA in fluid samples.

RESULTS

Epithelial lining fluid from active sarcoids contained elevated levels of interleukin-18, interferon-gamma, and interleukin-12 compared with recovered patients and also contained significantly higher levels of endotoxin. Depletion of endotoxin from this epithelial lining fluid reduced its effect on the human interleukin-18 promoter in vitro. There was a higher frequency of the -607C allele and -607(C/C) genotype in the sarcoidosis population compared with control subjects; however, this was not associated with a functional response to endotoxin treatment. Finally, bacterial 16S rRNA from Haemophilus influenzae and Moraxella catarrhalis was detected in sarcoid fluid samples.

CONCLUSIONS

The pathogenesis of sarcoidosis is propagated through the actions of a helper T-cell type 1-driven response. This study shows that gram-negative bacteria may contribute to this effect by upregulating interleukin-18 expression.