Rare genetic variants provide a mechanistic basis for immune imbalance in IgG4-related disease.

Autoimmune diseases are commonly associated with a polygenic inheritance pattern. In rare instances, causal monogenic variants have been identified. The study by Liu et al. in this issue of the JCI provides an example of monogenic variants occurring in patients with IgG4-related disease (IgG4-RD). The authors investigated a familial cluster of IgG4-RD that consisted of an affected father and two daughters; the mother was unaffected. Genome sequencing of this quad identified a variant in IKZF1 (encoding IKAROS) and another variant in UBR4 (encoding E3 ubiquitin ligase). Both variants were present in the father and both daughters but absent in the unaffected mother. Using multidimensional profiling of immune cells and functional experiments in primary cells, the authors determined a molecular pathway contributing to T cell activation in IgG4-RD. Importantly, the characterization of these variants provides insights into pathogenic mechanisms in IgG4-RD and, potentially, other autoimmune diseases.

IKZF1 and UBR4 gene variants drive autoimmunity and Th2 polarization in IgG4-related disease.

IgG4-related disease (IgG4-RD) is a systemic immune-mediated fibroinflammatory disease whose pathomechanisms remain poorly understood. Here, we identified gene variants in familial IgG4-RD and determined their functional consequences. All 3 affected members of the family shared variants of the transcription factor IKAROS, encoded by IKZF1, and the E3 ubiquitin ligase UBR4. The IKAROS variant increased binding to the FYN promoter, resulting in higher transcription of FYN in T cells. The UBR4 variant prevented the lysosomal degradation of the phosphatase CD45. In the presence of elevated FYN, CD45 functioned as a positive regulatory loop, lowering the threshold for T cell activation. Consequently, T cells from the affected family members were hyperresponsive to stimulation. When transduced with a low-avidity, autoreactive T cell receptor, their T cells responded to the autoantigenic peptide. In parallel, high expression of FYN in T cells biased their differentiation toward Th2 polarization by stabilizing the transcription factor JunB. This bias was consistent with the frequent atopic manifestations in patients with IgG4-RD, including the affected family members in the present study. Building on the functional consequences of these 2 variants, we propose a disease model that is not only instructive for IgG4-RD but also for atopic diseases and autoimmune diseases associated with an IKZF1 risk haplotype.

IgG4-related disease and B-cell malignancy due to an IKZF1 gain-of-function variant.

BACKGROUND: Monoallelic loss-of-function IKZF1 (IKAROS) variants cause B-cell deficiency or combined immunodeficiency, whereas monoallelic gain-of-function (GOF) IKZF1 variants have recently been reported to cause hypergammaglobulinemia, abnormal plasma cell differentiation, autoimmune and allergic manifestations, and infections. OBJECTIVE: We studied 7 relatives with autoimmune/inflammatory and lymphoproliferative manifestations to identify the immunologic disturbances and the genetic cause of their disease. METHODS: We analyzed biopsy results and performed whole-exome sequencing and immunologic studies. RESULTS: Disease onset occurred at a mean age of 25.2 years (range, 10-64, years). Six patients suffered from autoimmune/inflammatory diseases, 4 had confirmed IG4-related disease (IgG4-RD), and 5 developed B-cell malignancies: lymphoma in 4 and multiple myeloma in the remaining patient. Patients without immunosuppression were not particularly prone to infectious diseases. Three patients suffered from life-threatening coronavirus disease 2019 pneumonia, of whom 1 had autoantibodies neutralizing IFN-α. The recently described IKZF1 GOF p.R183H variant was found in the 5 affected relatives tested and in a 6-year-old asymptomatic girl. Immunologic analysis revealed hypergammaglobulinemia and high frequencies of certain lymphocyte subsets (exhausted B cells, effector memory CD4 T cells, effector memory CD4 T cells that have regained surface expression of CD45RA and CD28-CD57+ CD4+ and CD8+ T cells, TH2, and Tfh2 cells) attesting to immune dysregulation. Partial clinical responses to rituximab and corticosteroids were observed, and treatment with lenalidomide, which promotes IKAROS degradation, was initiated in 3 patients. CONCLUSIONS: Heterozygosity for GOF IKZF1 variants underlies autoimmunity/inflammatory diseases, IgG4-RD, and B-cell malignancies, the onset of which may occur in adulthood. Clinical and immunologic data are similar to those for patients with unexplained IgG4-RD. Patients may therefore benefit from treatments inhibiting pathways displaying IKAROS-mediated overactivity.

Single-cell RNA sequencing of submandibular gland reveals collagen type XV-positive fibroblasts as a disease-characterizing cell population of IgG4-related disease.

OBJECTIVES: IgG4-related disease (IgG4-RD) is a systemic autoimmune disease with an unknown etiology, affecting single/multiple organ(s). Pathological findings include the infiltration of IgG4-producing plasma cells, obliterative phlebitis, and storiform fibrosis. Although immunological studies have shed light on the dysregulation of lymphocytes in IgG4-RD pathogenesis, the role of non-immune cells remains unclear. This study aimed to investigate the demographics and characteristics of non-immune cells in IgG4-RD and explore potential biomarkers derived from non-immune cells in the sera. METHODS: We conducted single-cell RNA sequence (scRNA-seq) on non-immune cells isolated from submandibular glands of IgG4-RD patients. We focused on fibroblasts expressing collagen type XV and confirmed the presence of those fibroblasts using immunohistochemistry. Additionally, we measured the levels of collagen type XV in the sera of IgG4-RD patients. RESULTS: The scRNA-seq analysis revealed several distinct clusters consisting of fibroblasts, endothelial cells, ductal cells, and muscle cells. Differential gene expression analysis showed upregulation of COL15A1 in IgG4-RD fibroblasts compared to control subjects. Notably, COL15A1-positive fibroblasts exhibited a distinct transcriptome compared to COL15A1-negative counterparts. Immunohistochemical analysis confirmed a significant presence of collagen type XV-positive fibroblasts in IgG4-RD patients. Furthermore, immune-suppressive therapy in active IgG4-RD patients resulted in decreased serum levels of collagen type XV. CONCLUSIONS: Our findings suggest that collagen type XV-producing fibroblasts may represent a disease-characterizing non-immune cell population in IgG4-RD and hold potential as a disease-monitoring marker.

HLA-DRB1 Is Associated with Therapeutic Responsiveness in IgG4-related Disease.

Objective Glucocorticoids are key drugs used in remission induction therapy for IgG4-related disease (IgG4-RD). However, the therapeutic outcomes vary widely, with some patients requiring long-term maintenance therapy and others relapsing repeatedly, whereas still others can tolerate withdrawal. These variations underscore the need for personalized treatment strategies for IgG4-RD. We examined the relationship between human leukocyte antigen (HLA) genotypes and the response to glucocorticoid treatment in patients with IgG4-RD. Methods Eighteen IgG4-RD patients visiting our hospital were included in the study. Peripheral blood samples were collected, HLA genotypes were determined, and the response to glucocorticoid treatment (maintenance dose at the time of last observation, glucocorticoid dose when the serum IgG4 level was the lowest after remission induction therapy, and occurrence of relapse) was examined retrospectively. Results The DQB1*12:01 genotypes were associated with a prednisolone maintenance dose of <7 mg/day. A prednisolone dose ≥10 mg with a minimum serum IgG4 level was significantly more common in B*40:01 and DRB1-GB-7-Val (DRB1*04:01, *04:03, *04:05, *04:06, and *04:10) patients than other alleles. Relapse also tended to be more common in DRB1-GB-7-Val carriers than other alleles. Conclusion These data suggest that HLA-DRB1 is associated with glucocorticoid treatment responsiveness and is important for follow-up monitoring of serum IgG4 levels during glucocorticoid tapering. We believe that these data will contribute to the future development of personalized medicine for IgG4-RD.

Single-Cell RNA-Sequencing Reveals Peripheral T Helper Cells Promoting the Development of IgG4-Related Disease by Enhancing B Cell Activation and Differentiation.

Abnormal B cell differentiation plays a critical role in IgG4-related disease (IgG4-RD), but the underlying mechanism remains largely unknown. We investigated the cell landscape from three IgG4-RD retroperitoneal tissues and three control tissues using single-cell RNA-sequencing. Critical cell type or markers were further validated in the peripheral blood from the patients with IgG4-RD and healthy controls via flow cytometry as well as in the IgG4-RD and control tissue via immunofluorescence staining. The increases in B cells, plasma cells, and CD4+ T cells were found in IgG4-RD retroperitoneal tissue. Importantly, among CD4+ T cells, an increase in CD4+CXCR5-PD1hi peripheral T helper (Tph) cells with a high expression of IL-21 and TIGIT was discovered in IgG4-RD tissue, which was further validated in peripheral blood of the patients with IgG4-RD. The Tph cell and TIGIT+ Tph cell proportion were remarkably higher in active IgG4-RD patients and correlated with disease activity. Moreover, TIGIT+CD4+ cells were able to promote B cell differentiation via IL-21. Our study revealed that Tph cells are increased in IgG4-RD and probably play critical roles in B cell differentiation through TIGIT-IL-21 axis. Peripheral Tph cell and TIGIT+Tph cell are potential markers for IgG4-RD disease activity.

Single-cell transcriptome analysis and protein profiling reveal broad immune system activation in IgG4-related disease.

IgG4-related disease (IgG4-RD) is a systemic autoimmune disease with unclear pathogenesis. We performed single-cell RNA-seq and surface proteome analyses on 61,379 PBMCs from 9 treatment-naive IgG4-RD patients and 7 age- and sex-matched healthy controls. Integrative analyses were performed for altered gene expression in IgG4-RD, and flow cytometry and immunofluorescence were used for validation. We observed expansion of plasmablasts with enhanced protein processing and activation, which correlated with the number of involved organs in IgG4-RD. Increased proportions of CD4+ cytotoxic T lymphocytes (CTLs), CD8+ CTLs-GNLY (granulysin), and γδT cells with enhanced chemotaxis and cytotoxicity but with suppressed inhibitory receptors characterize IgG4-RD. Prominent infiltration of lymphocytes with distinct compositions were found in different organs of IgG4-RD patients. Transcription factors (TFs), including PRDM1/XBP1 and RUNX3, were upregulated in IgG4-RD, promoting the differentiation of plasmablasts and CTLs, respectively. Monocytes in IgG4-RD have stronger expression of genes related to cell adhesion and chemotaxis, which may give rise to profibrotic macrophages in lesions. The gene activation pattern in peripheral immune cells indicated activation of multiple interaction pathways between cell types, in part through chemokines or growth factors and their receptors. Specific upregulation of TFs and expansion of plasmablasts and CTLs may be involved in the pathogenesis of IgG4-RD, and each of these populations are candidate targets for therapeutic interventions in this disease.

Single-cell transcriptome analysis profiles cellular and molecular alterations in submandibular gland and blood in IgG4-related disease.

OBJECTIVES: The aim of this study is to profile the transcriptional landscapes of affected tissues and peripheral blood mononuclear cells (PBMCs) at the single-cell level in IgG4-related disease (IgG4-RD). Identifying the cell populations and crosstalk between immune cells and non-immune cells will assist us in understanding the aetiology of IgG4-RD. METHODS: We performed single-cell RNA sequencing analysis on submandibular glands (SMGs) and PBMCs from patients with IgG4-RD and matched controls. Additionally, bulk RNA sequencing of PBMCs was used to construct the immune repertoire. Furthermore, multiplex immunofluorescence staining was performed to validate the transcriptomic results. RESULTS: We identified three novel subsets of tissue-resident immune cells in the SMGs of patients with IgG4-RD. TOP2A_B cells and TOP2A_T cells had stemness signatures, and trajectory analysis showed that TOP2A_B cells may differentiate into IgG4+plasma cells and that TOP2A_T cells may differentiate into T follicular helper (Tfh) cells. ICOS_PD-1_B cells with Tfh-like characteristics appeared to be an intermediate state in the differentiation from B cells to IgG4+plasma cells. The cellular communication patterns within immune cells and between immune cells and non-immune cells were altered in IgG4-RD compared with controls. Consistently, infection-related pathways were shared in B cells and T cells from SMGs and PBMCs. Furthermore, immune clonotype analysis of PBMC samples showed the complementary determining region 3 amino acid CQQSYSTPYTF was expanded in patients with IgG4-RD. CONCLUSION: Our data revealed the cellular and molecular changes at the single-cell resolution of IgG4-RD and provide valuable insights into the aetiology and novel therapeutic targets of the autoimmune disease.

Differential CpG DNA methylation of peripheral B cells, CD4+ T cells, and salivary gland tissues in IgG4-related disease.

OBJECTIVES: Immunoglobulin-G4-related disease (IgG4-RD) is a distinct systemic autoimmune-mediated disease manifesting as chronic inflammation and tissue fibrosis. Since the role of DNA methylation in the pathogenesis of IgG4-RD is still unclear, we conduct this study to investigate epigenetic modifications in IgG4-RD. METHODS: A genome-wide DNA methylation study was conducted with B cells, CD4+ T cells, and salivary gland tissues from IgG4-RD patients and matched controls by using the Illumina HumanMethylation 850K BeadChip. We further performed pyrosequencing and immunohistochemistry assays to validate the methylation status of some targets of interest. RESULTS: We identified differentially methylated CpG sites including 44 hypomethylated and 166 hypermethylated differentially methylated probes (DMPs) in B cells and 260 hypomethylated and 112 hypermethylated DMPs in CD4+ T cells from 10 IgG4-RD patients compared with 10 healthy controls. We also identified 36945 hypomethylated and 78380 hypermethylated DMPs in salivary gland tissues of 4 IgG4-RD patients compared with 4 controls. DPM2 (cg21181453), IQCK (cg10266221), and ABCC13 (cg05699681, cg04985582) were hypermethylated and MBP (cg18455083) was hypomethylated in B cells, CD4+ T cells, and salivary gland tissues of IgG4-RD patients. We also observed the hypomethylated HLA-DQB2 in CD4+ T cells from IgG4-RD patients. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of DMPs in salivary gland tissues of IgG4-RD patients revealed enrichment of pathways involved in the regulation of immune cell responses and fibrosis. CONCLUSION: This is the first DNA methylation study in peripheral B cells, CD4+ T cells, and salivary gland tissues from IgG4-RD patients. Our findings highlighted the role of epigenetic modification of DNA methylation and identified several genes and pathways possibly involved in IgG4-RD pathogenesis.

Id4 modulates salivary gland homeostasis and its expression is downregulated in IgG4-related disease via miR-486-5p.

Salivary glands are physiologically orchestrated by the coordinated balance between cell differentiation, proliferation, apoptosis, and interactions between epithelial, mesenchymal endothelial, and neuronal cells, and they are frequent sites of manifestations of Sjögren's syndrome (SS) or IgG4-related disease (IgG4-RD). However, little is known about salivary gland homeostasis and its involvement in those diseases. Inhibitor of DNA binding/differentiation 4 (Id4) is an Id protein involved in the transcriptional control of many biological events, including differentiation. Studies of Id4-deficient mice revealed that Id4-deficient submandibular glands were smaller and exhibited accelerated differentiation, compared with those from wild-type littermates. In addition, dry mouth symptoms and Th17 expansion in splenocytes were also observed in the absence of Id4. Furthermore, Id4 levels in the salivary glands of patients with IgG4-RD, but not SS, were significantly decreased compared with those of healthy controls. miRNA-mRNA integrated analysis demonstrated that miR-486-5p was upregulated in IgG4-RD patients and that it might regulate Id4 in the lesion sites. Together, these results provide evidence for the inhibitory role of Id4 in salivary differentiation, and a critical association between Id4 downregulation and IgG4-RD.

IL1R1 gene variants associate with disease susceptibility to IgG4-related periaortitis/periarteritis in IgG4-related disease.

BACKGROUND: IgG4-related disease (IgG4-RD) is an immune-mediated disorder characterized by high serum IgG4 concentration and IgG4-bearing plasma cell infiltration in affected organs. IgG4-related periaortitis/periarteritis is a recently identified disease entity in IgG4-RD that affects the cardiovascular system. Since the genetic factors related to disease onset are unclear, we examined the genetic associations with IgG4-related periaortitis/periarteritis susceptibility. METHODS: A small scale of genome-wide association analysis identified that interleukin 1 receptor type 1 (IL1R1) gene variants were correlated with the development of IgG4-related periaortitis/periarteritis in 75 patients with IgG4-RD. Accordingly, 8 single nucleotide polymorphisms (SNPs) in the IL1R1 gene were selected and genotyped in 124 patients with IgG4-RD (43 with periaortitis/periarteritis and 81 without periaortitis/periarteritis) and 344 healthy subjects. RESULTS: The minor allele frequencies of 6 SNPs (rs2287049, rs3917273, rs2160227, rs951192, rs3917318, rs7582198) were significantly increased in IgG4-related periaortitis/periarteritis patients compared with those without periaortitis/periarteritis (corrected P < 0.05). In addition, the frequency of the AGAAA haplotype, comprised of 5 SNPs (rs3917273, rs2160227, rs951192, rs3917318, rs7582198), was significantly higher in patients with periaortitis/periarteritis (OR = 2.41, 95% CI:1.42-4.10). CONCLUSION: Our findings indicated that IL1R1 genetic polymorphisms contributed to IgG4-related periaortitis/periarteritis and the possibility of certain genetic factors influencing the risk of specific IgG4-RD manifestations.

Disparities between IgG4-related kidney disease and extrarenal IgG4-related disease in a case-control study based on 450 patients.

We aimed to compare the demographic, clinical and laboratory characteristics between IgG4-related kidney disease (IgG4-RKD+) and extrarenal IgG4-related disease (IgG4-RKD-) in a large Chinese cohort, as well as describing the radiological and pathological features of IgG4-RKD+. We retrospectively analyzed the medical records of 470 IgG4-related disease (IgG4-RD) patients at Peking University People's Hospital from January 2004 to January 2020. The demographic, clinical, laboratory, radiological and pathological characteristics between IgG4-RKD+ and IgG4-RKD- were compared. Twenty IgG4-RD patients who had definite etiology of renal impairment including diabetes, hypertension and etc. were excluded. Among the remained 450 IgG4-RD patients, 53 were diagnosed with IgG4-RKD+ . IgG4-RKD+ patients had older age at onset and at diagnosis. Male to female ratio of IgG4-RKD+ patients is significantly higher. In the IgG4-RKD+ group, the most commonly involved organs were salivary gland, lymph nodes and pancreas. It was found that renal function was impaired in approximately 40% of IgG4-RKD+ patients. The most common imaging finding is multiple, often bilateral, hypodense lesions. Male sex, more than three organs involved, and low serum C3 level were risk factors for IgG4-RKD+ in IgG4-RD patients. These findings indicate potential differences in pathogenesis of these two phenotypes.

The pronounced lung lesions developing in LATY136F knock-in mice mimic human IgG4-related lung disease.

RATIONALE: Immunoglobulin (Ig) G4-related disease (IgG4-RD) is a novel clinical disease entity characterized by an elevated serum IgG4 concentration and tumefaction or tissue infiltration by IgG4-positive plasma cells. Pathological changes are most frequently seen in the pancreas, lacrimal glands, and salivary glands, but pathological changes in the lung also exist. Linker for activation of T cell (LAT)Y136F knock-in mice show Th2-dominant immunoreactions with elevated serum IgG1 levels, corresponding to human IgG4. We have reported that LATY136F knock-in mice display several characteristic features of IgG4-RD and concluded that they constitute an appropriate model of human IgG4-RD in salivary glands, pancreas, and kidney lesions. OBJECTIVES: The aim of this study is to evaluate whether lung lesions in LATY136F knock-in mice can be a model of IgG4-related lung disease. METHODS: Lung tissue samples from LATY136F knock-in mice (LAT) and wild-type mice (WT) were immunostained for IgG1 and obtained for pathological evaluation, and cell fractions and cytokine levels in broncho-alveolar lavage fluid (BALF) were analyzed. RESULTS: In the LAT group, IgG1-positive inflammatory cells increased starting at 4 weeks of age and peaked at 10 weeks of age. The total cell count and percentage of lymphocytes increased significantly in BALF in the LAT group compared to the WT group. In BALF, Th2-dominant cytokines and transforming growth factor-ß were also increased. In the LAT group, marked inflammation around broncho-vascular bundles peaked at 10 weeks of age. After 10 weeks, fibrosis around broncho-vascular bundles and bronchiectasis were observed in LATY136F knock-in mice but not WT mice. CONCLUSIONS: LATY136F knock-in mice constitute an appropriate model of lung lesions in IgG4-RD.

CGRP-Mediated Prolactin Upregulation: a Possible Pathomechanism in IgG4-Related Disease.

Similar to other immune-mediated diseases, IgG4-related disease (IgG4-RD) is the disease that develops in genetically susceptible individuals exposed to external or endogenous antigens. In the present study, it was confirmed that MAG (myelin-associated glycoprotein) antibodies (IgG, IgG4, and IgM) were detected by immunofluorescence (IFA) in serum of the patients with IgG4-RD. In vivo, the levels of prolactin and Th2 cytokines in CGRP+/- rats were higher than those in wild-type. Our findings indicate that the presence of CGRP-deficiency-mediated MAG antibodies is a probable molecular basis for the initial events which were triggered in IgG4-RD immune responses via prolactin upregulation.

Multiple Processes May Involve in the IgG4-RD Pathogenesis: An Integrative Study via Proteomic and Transcriptomic Analysis.

Immunoglobulin G4-related disease (IgG4-RD) is a newly defined disease entity, while the exact pathogenesis is still not clear. Identifying the characters of IgG4-RD in proteomic and transcriptomic aspects will be critical to investigate the potential pathogenic mechanisms of IgG4-RD. We performed proteomic analysis realized with iTRAQ technique for serum samples from eight treatment-naive IgG4-RD patients and eight healthy volunteers, and tissue samples from two IgG4-RD patients and two non-IgG4-RD patients. Transcriptomic data (GSE40568 and GSE66465) was obtained from the GEO Dataset for validation. The weighted correlation network analysis (WGCNA) was applied to detect the gene modules correlated with IgG4-RD. KEGG pathway analysis was used to investigate pathways enriched in IgG4-RD samples. As a result, a total of 980 differentially expressed proteins (DEPs) in tissue and 94 DEPs in serum were identified between IgG4-RD and control groups. Three hundred fifty-four and two hundred forty-seven genes that most correlated with IgG4-RD were detected by WGCNA analysis in tissue and PBMC, respectively. We also found that DEPs in IgG4-RD samples were enriched in several immune-related activities including bacterial/viral infections and platelet activation as well as some immune related signaling pathways. In conclusion, we identified multiple processes/factors and several signaling pathways that may involve in the IgG4-RD pathogenesis, and found out some potential therapeutic targets for IgG4-RD.

The Cellular and Molecular Bases of Allergy, Inflammation and Tissue Fibrosis in Patients with IgG4-related Disease.

IgG4-related disease (IgG4-RD) is a spectrum of complex fibroinflammatory disorder with protean manifestations mimicking malignant neoplasms, infectious or non-infectious inflammatory process. The histopathologic features of IgG4-RD include lymphoplasmacytic infiltration, storiform fibrosis and obliterative phlebitis together with increased in situ infiltration of IgG4 bearing-plasma cells which account for more than 40% of all IgG-producing B cells. IgG4-RD can also be diagnosed based on an elevated serum IgG4 level of more than 110 mg/dL (normal < 86.5 mg/mL in adult) in conjunction with protean clinical manifestations in various organs such as pancreato-hepatobiliary inflammation with/without salivary/lacrimal gland enlargement. In the present review, we briefly discuss the role of genetic predisposition, environmental factors and candidate autoantibodies in the pathogenesis of IgG4-RD. Then, we discuss in detail the immunological paradox of IgG4 antibody, the mechanism of modified Th2 response for IgG4 rather than IgE antibody production and the controversial issues in the allergic reactions of IgG4-RD. Finally, we extensively review the implications of different immune-related cells, cytokines/chemokines/growth factors and Toll-like as well as NOD-like receptors in the pathogenesis of tissue fibro-inflammatory reactions. Our proposals for the future investigations and prospective therapeutic strategies for IgG4-RD are shown in the last part.

Pathophysiology of IgG4-related disease: A T follicular helper cells disease?

IgG4-related disease is a chronic inflammatory disease characterized by clinical, biological and pathological unifying findings. Because these criteria are not always all together available in patients and because biological and pathological markers are not totally specific, the diagnosis should be retained after exclusion of mimickers. Since the individualization of IgG4-RD, several studies have allowed to better characterize immunological abnormalities associated with this particular condition. B and T cell oligoclonal activation is associated with T helper 2 cytokine production leading to IgG4 production and profibrotic cytokine release. A central role for T follicular helper 2 cells is suggested from recent findings. We summarize here recent advances in understanding of immune abnormalities in IgG4-related disease.

Alteration of Cell Surface Markers CD38 and CD138 in Lymphoproliferative Disorders in the Ocular Adnexa.

BACKGROUND/AIM: CD38 is a cell surface marker commonly present in plasma cells and activated T cells, while CD138 is a representative plasma cell marker. The aim of this study was to describe the expression of cell surface markers including CD38 and CD138, in the tumors of patients with IgG4-related ophthalmic disease (IgG4-ROD) and extranodal marginal zone B-cell lymphoma (EMZL) of the ocular adnexa. MATERIALS AND METHODS: Twenty-four consecutive patients of whom 12 had IgG4-ROD and 12 EMZL were enrolled in this study. Medical records were reviewed for flow cytometry (FCM) results on conventional T-cell markers, B-cell markers, CD38 and CD138. RESULTS: Positive rates of T-cell markers, CD38 and CD138 were significantly higher in IgG4-ROD than in EMZL (p<0.01 and p<0.05, respectively). CONCLUSION: Our FCM results on CD38 and CD138 showed that the lymphocyte populations were different between IgG4-ROD and EMZL, which may reflect the different pathophysiology of the two diseases.

Pathogenesis of IgG4-related disease. Comparison with Sjögren's syndrome.

IgG4-related disease (IgG4-RD) is characterized by lympho-plasmacytic infiltration and fibrosis in multiple organs, accompanied by high serum IgG4 levels. Although both IgG4-RD and Sjögren's syndrome (SS) frequently affect salivary and lacrimal glands, the clinical and pathological features of these two conditions are different. In an attempt to delineate the pathomechanisms of IgG4-RD, we compared the gene expression patterns of various molecules in labial salivary glands (LSGs) between IgG4-RD and SS. First, using quantitative PCR, we demonstrated significantly higher mRNA expression levels of activation-induced cytidine deaminase (AID), IL-10, and TGFß in LSGs of IgG4-RD than SS and healthy controls (HCs). We propose that the combination of AID and IL-10 contributes to IgG4-specific immunoglobulin class switch recombination, and that TGFß induces LSGs fibrosis in IgG4-RD. Second, DNA microarray identified 2641 differentially expressed genes (DEGs) in LSGs; with 1321 up-regulated and 1320 down-regulated genes in IgG4-RD, relative to SS. Among the up-regulated DEGs in IgG4-RD, quantitative PCR confirmed significantly higher expression levels of chemokine (C-C motif) ligand 18 (CCL18) and lactotransferrin in LSGs of IgG4-RD than SS and HCs. The former has chemotactic activity on various types of lymphocytes and enhances collagen production from fibroblasts, while lactotransferrin is an iron-binding protein abundantly present in milk and has a wide range of functions, including fibroblast proliferation and maturation of dendritic cells (DCs). Third, immunofluorescence staining confirmed specific upregulation of CCL18 in macrophages, CD11c + and B cells, and plasmacytes of LSGs-IgG4-RD. These pathological findings could help in the identification of disease-specific biomarkers as well as development of novel therapeutic strategies.

The broad and challenging landscape of extranodal lymphoproliferations.

Two sessions in the workshop of the 19th meeting of the European Association for Haematopathology termed "challenging extranodal lymphoproliferations" and "extranodal non-site-specific lymphoproliferations", dealt with a series of heterogenous cases. These included lymphoproliferations of all cell lineages, from reactive lesions mimicking lymphomas through indolent lymphoid neoplasia and tumours with unclear biological behaviour to aggressive and transformed lymphomas. The themes addressed included cases with borderline features between hyperplastic and neoplastic lesions, the diagnostic spectrum of IgG4-related disease, T cell lymphoproliferations arising in extranodal sites with presumed indolent behaviour, diverse clinical presentations of intravascular large B cell lymphoma, diagnostic problems encountered with tumours displaying plasmablastic morphology, pitfalls concerning rare entities like adult T cell lymphoma/leukaemia (ATLL) and extranodal natural killer/T cell (NK/T) lymphomas, and unusual clinical presentations of various lymphomas. Altogether, within the frame of these two sessions, 75 cases remarkably differing in their clinical background, genetic features and overall need for a meticulous diagnostic approach were presented and discussed. In this paper, the salient points raised during the discussion of the cases, current diagnostic concepts and recommendations relevant to the diagnosis of these lymphoproliferations are described.