Increased monocyte Fc(IgG) receptor expression in sarcoidosis

Altered transcription factor targeting is associated with differential peripheral blood mononuclear cell proportions in sarcoidosis

Introduction

In sarcoidosis, peripheral lymphopenia and anergy have been associated with increased inflammation and maladaptive immune activity, likely promoting development of chronic and progressive disease. However, the molecular mechanisms that lead to reduced lymphocyte proportions, particularly CD4+ T-cells, have not been fully elucidated. We posit that paradoxical peripheral lymphopenia is characterized by a dysregulated transcriptomic network associated with cell function and fate that results from altered transcription factor targeting activity.

Methods

Messenger RNA-sequencing (mRNA-seq) was performed on peripheral blood mononuclear cells (PBMCs) from ACCESS study subjects with sarcoidosis and matched controls and findings validated on a sarcoidosis case-control cohort and a sarcoidosis case series. Preserved PBMC transcriptomic networks between case-control cohorts were assessed to establish cellular associations with gene modules and define regulatory targeting involved in sarcoidosis immune dysregulation utilizing weighted gene co-expression network analysis and differential transcription factor involvement analysis. Network centrality measures identified master transcriptional regulators of subnetworks related to cell proliferation and death. Predictive models of differential PBMC proportions constructed from ACCESS target gene expression corroborated the relationship between aberrant transcription factor regulatory activity and imputed and clinical PBMC populations in the validation cohorts.

Results

We identified two unique and preserved gene modules significantly associated with sarcoidosis immune dysregulation. Strikingly, increased expression of a monocyte-driven, and not a lymphocyte-driven, gene module related to innate immunity and cell death was the best predictor of peripheral CD4+ T-cell proportions. Within the gene network of this monocyte-driven module, TLE3 and CBX8 were determined to be master regulators of the cell death subnetwork. A core gene signature of differentially over-expressed target genes of TLE3 and CBX8 involved in cellular communication and immune response regulation accurately predicted imputed and clinical monocyte expansion and CD4+ T-cell depletion.

Conclusions

Altered transcriptional regulation associated with aberrant gene expression of a monocyte-driven transcriptional network likely influences lymphocyte function and survival. Although further investigation is warranted, this indicates that crosstalk between hyperactive monocytes and lymphocytes may instigate peripheral lymphopenia and underlie sarcoidosis immune dysregulation and pathogenesis. Future therapies selectively targeting master regulators, or their targets, may mitigate dysregulated immune processes in sarcoidosis and disease progression.

FCGR3A and FCGR3B copy number variations are risk factors for sarcoidosis

Sarcoidosis is a multisystem granulomatous disorder that causes significant morbidity. Genetic factors contribute to sarcoidosis risks. In this study, we investigated whether copy number variations (CNVs) of FCGR3A (coding for FcγRIIIA) and FCGR3B (coding for FcγRIIIB) genes are associated with sarcoidosis susceptibility and whether the expressions of FcγRIIIA on NK cells and FcγRIIIB on neutrophils are altered in sarcoidosis patients. TaqMan real-time PCR assays were used to analyze the CNV of FCGR3A and FCGR3B genes. FCGR3A and FCGR3B CNV genotypes were compared between 671 biopsy-proven sarcoidosis patients and the same number of healthy controls matched with age, sex, race, and geographic area from the ACCESS (A Case Control Etiologic Study of Sarcoidosis) cohort. Flow cytometry analyses were used to determine expressions of FcγRIIIA on NK cells and FcγRIIIB on neutrophils in phenotype analyses. We found that FCGR3A CNVs were significantly associated with sarcoidosis in females (CN = 1 vs. CN = 2 logistic regression adjusted for sex and race, OR 4.0156, SE = 2.2784, P = 0.0143; CN = 3 vs. CN = 2 logistic regression adjusted for sex and race, OR 2.8044, SE = 1.1065, P = 0.0090), suggesting that FCGR3A gene abnormality influences sarcoidosis development in a gender-specific manner. Furthermore, FcγRIIIA expressions were significantly decreased on NK cells from sarcoidosis patients compared to those from healthy controls (P = 0.0007). Additionally, low FCGR3B CN was associated with sarcoidosis (CN <2 vs. CN = 2 logistic regression adjusted for sex and race, OR 1.5025, SE = 0.2682, P = 0.0226), indicating that the functions of FCGR3B gene may also contribute to the pathogenesis of sarcoidosis. We conclude that FCGR3A CNVs are a major risk factor for female sarcoidosis and FCGR3B CNVs may also affect the development of sarcoidosis.

Immunology of sarcoidosis

Because of its association with cutaneous anergy, sarcoidosis was originally viewed as a defect of cellular immunity. Supporting that misperception were early studies of peripheral blood lymphocytes that found lymphopenia and impaired lymphocyte responses to mitogens and recall antigens. The clue to a vast underlying network of complex hyperactive cellular immune functions was discovered in the paradoxical finding of in vitro spontaneous lymphoblastic transformation and lymphokine production. Subsequently, investigative focus shifted to the activated, proliferating T-helper lymphocytes, the lymphokines of which were found to function in the recruitment and retention of monocytes for granuloma development. T-helper lymphocytes also contributed to the mechanism of hypergammaglobulinemia through their influence on B cells. The most intriguing question about sarcoid immunology is the initiating factor that triggers the T-lymphocyte activation and proliferation in the first place. There is much to suggest that antigen processing and presentation launches the process. Because lymphocyte activation and proliferation antedate granuloma formation at K-S skin test sites and in the lung, we combined the harvesting technique of BAL with the K-S bioassay to show that granulomagenic antigen is being processed by monocyte-macrophages. The finding of autologous monocyte-macrophage granulomagenicity raises the distinct possibility that sarcoidosis is a unique cell-mediated type of autoimmune process. The isolation and identification of the granulomagenic factor is the exciting research frontier ahead.

Expression of the CD11/CD18 cell surface adhesion glycoprotein family and MHC class II antigen on blood monocytes and alveolar macrophages in interstitial lung diseases

The expression of molecules of the CD11/CD18 cell surface adhesion glycoprotein family and HLA/DR antigen was studied on peripheral blood monocytes (PBM) and alveolar macrophages (AM) in bronchoalveolar lavage (BAL) fluid from patients with sarcoidosis, idiopathic pulmonary fibrosis (IPF), and extrinsic allergic alveolitis (EAA). Patients with these interstitial lung diseases showed increased numbers of macrophages in BAL fluid. This was probably caused by an increased influx of PBM to the alveoli since the numbers of cells with a monocytic morphology were also significantly increased in BAL samples from patients with interstitial lung disease, most prominently in IPF and EAA. The increased influx of PBM into the alveoli in patients with interstitial lung diseases was not reflected by an increased expression of the CD11/CD18 leukocyte function antigens on PBM. In healthy volunteers as well as in those with sarcoidosis, IPF, and EAA, the percentages of AM positive for CD11b (the C3bi complement receptor) and CD11c were lower than among PBM. This indicates that the expression of these cell surface adhesion molecules is downregulated during maturation and migration of PBM to the alveoli. The absolute numbers of AM positive for CD11b were increased in BAL fluid of IPF and EAA patients compared to healthy volunteers. EAA patients also showed increased absolute numbers of AM positive for CD11a and CD11c. This differentially increased expression of these leukocyte function antigens on AM suggests the influence of locally produced cytokines.