Association Study and Fine-Mapping Major Histocompatibility Complex Analysis of Pemphigus Vulgaris in a Han Chinese Population

Patient genetics shape the autoimmune response in the blistering skin disease pemphigus vulgaris

Background and aim

Pemphigus vulgaris (PV) is known to have one of the strongest HLA associations among autoimmune diseases. DRB1*0402 and DQB1*0503 in particular are significantly overrepresented in PV patients in certain worldwide populations. Yet, there remain significant gaps in our understanding regarding the precise link between PV-associated HLA molecules, the specificity of the autoimmune response, and clinical expression. In this study we assessed correlations between factors including HLA genotype, ethnicity, autoantibody levels, and lesion distribution in a cohort of 293 patients.

Methods and population

Participants were recruited from multiple outpatient dermatology clinic settings and patient support meetings in the USA. On intake, patients provided venous blood samples and answered questionnaires regarding their current disease activity.

Results

Eighty-one percent of patients typed as either DRB1*0402 or DQB1*0503 with a high prevalence of DRB1*0402 in patients of Ashkenazi Jewish or Caucasian (non-Jewish) descent (86% and 42%, respectively) and DQB1*0503 in patients of Southeast Asian descent (78%). Patients typing as HLA DRB1*0402 had higher levels of anti-desmoglein (Dsg)3 antibodies (204.6 +/- 340.5 IU/ml) than patients without DRB1*0402 (138.5 +/- 236.4 IU/ml) (p=0.03) and had mucosal only lesions more often than cutaneous only or mucocutaneous lesions. Patients typing as DQB1*0503 had higher levels of anti-Dsg1 antibodies (47.3 +/- 59.8 IU/ml) compared to other groups (27.8 +/- 43.7 IU/ml) (p=0.06) and higher rates of mucocutaneous disease than other lesion types. We also report an unexpected HLA association of DRB1*0804 in PV patients of African descent. Sixty-four percent of this population carried the DRB1*0804 allele, and presented with highly elevated levels of anti-Dsg3 (p=0.02). However, neither African heritage nor the presence of DRB1*0804 correlated with a predilection to any specific lesion morphology. Patients that carried neither DRB1*0402, nor DQB1*0503 or DRB1*0804 had the lowest levels of anti-Dsg3 antibodies (60.0 +/- 80.0 IU/ml) and the highest rate of solely cutaneous disease compared to carriers of these alleles.

Conclusion

Our data illuminate the broader impact of genetic factors on disease development by showing that differences in HLA expression among patients and ethnicities play a large role in driving distinct patterns of antibody selection and disease phenotype in PV. These findings provide insights regarding clinical heterogeneity, and are relevant to developing improved, patient tailored management strategies.

Association of gut microbiome and metabolites with onset and treatment response of patients with pemphigus vulgaris

Background

Gut dysbiosis and gut microbiome-derived metabolites have been implicated in both disease onset and treatment response, but this has been rarely demonstrated in pemphigus vulgaris (PV). Here, we aim to systematically characterize the gut microbiome to assess the specific microbial species and metabolites associated with PV.

Methods

We enrolled 60 PV patients and 19 matched healthy family members, and collected 100 fecal samples (60 treatment-naïve, 21 matched post-treatment, and 19 controls). Metagenomic shotgun sequencing and subsequent quality control/alignment/annotation were performed to assess the composition and microbial species, in order to establish the association between gut microbiome with PV onset and treatment response. In addition, we evaluated short-chain fatty acids (SCFAs) in PV patients through targeted metabolomics analysis.

Results

The diversity of the gut microbiome in PV patients deviates from the healthy family members but not between responder and non-responder, or before and after glucocorticoid treatment. However, the relative abundance of several microbial species, including the pathogenic bacteria (e.g., Escherichia coli) and some SCFA-producing probiotics (e.g., Eubacterium ventriosum), consistently differed between the two groups in each comparison. Escherichia coli was enriched in PV patients and significantly decreased after treatment in responders. In contrast, Eubacterium ventriosum was enriched in healthy family members and significantly increased particularly in responders after treatment. Consistently, several gut microbiome-derived SCFAs were enriched in healthy family members and significantly increased after treatment (e.g., butyric acid and valeric acid).

Conclusions

This study supports the association between the gut microbiome and PV onset, possibly through disrupting the balance of gut pathogenic bacteria and probiotics and influencing the level of gut microbiome-derived SCFAs. Furthermore, we revealed the potential relationship between specific microbial species and glucocorticoid treatment.

Genome-wide association study of SNP- and gene-based approaches to identify susceptibility candidates for lupus nephritis in the Han Chinese population

Background

Lupus nephritis (LN) is one of the most common and serious complications of systemic lupus erythaematosus (SLE). Genetic factors play important roles in the pathogenesis of LN and could be used to predict who might develop LN. The purpose of this study was to screen for susceptible candidates of LN across the whole genome in the Han Chinese population.

Methods

592 LN patients and 453 SLE patients without renal damage were genotyped at 492,970 single nucleotide polymorphisms (SNPs) in the genome-wide association study (GWAS). Fifty-six SNPs were selected for replication in an independent cohort of 188 LN and 171 SLE without LN patients. Further quantitative real-time (qRT) PCR was carried out in 6 LN patients and 6 healthy controls. Gene-based analysis was conducted using the versatile gene-based test for GWAS. Subsequently, enrichment and pathway analyses were performed in the DAVID database.

Results

The GWAS analysis and the following replication research identified 9 SNPs showing suggestive correlation with LN (P<10-4). The most significant SNP was rs12606116 (18p11.32), at P=8.72×10−6. The qRT-PCR results verified the mRNA levels of LINC00470 and ADCYAP1, the closest genes to rs12606116, were significantly lower in LN patients. From the gene-based analysis, 690 genes had suggestive evidence of association (P<0.05), including LINC00470. The enrichment analysis identified the involvement of transforming growth factor beta (TGF-β) signalings in the development of LN. Lower plasma level of TGF-β1 (P<0.05) in LN patients and lower expression of transforming growth factor beta receptor 2 in lupus mice kidney (P<0.05) futher indicate the involvement of TGF-β in LN.

Conclusions

Our analyses identified several promising susceptibility candidates involved in LN, and further verification of these candidates was necessary.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

Epidemiology of Pemphigus

Pemphigus is an epidemiologically heterogeneous group of autoimmune bullous diseases comprising pemphigus vulgaris (PV), pemphigus foliaceus, paraneoplastic pemphigus, IgA pemphigus, and pemphigus herpetiformis. Recently, our knowledge about the frequency of pemphigus, which is highly variable between different populations, has considerably expanded, and the first non-HLA genes associated with PV have been identified. In addition, a variety of comorbidities, including other autoimmune diseases, hematological malignancies, and psoriasis, have been described in this variant. Here, initial data about the impact of COVID-19 on this fragile patient population are discussed and perspectives for future epidemiological studies are outlined.

ST18 affects cell-cell adhesion in pemphigus vulgaris in a tumour necrosis factor-α-dependent fashion

BACKGROUND

Pemphigus vulgaris (PV) is a life-threatening mucocutaneous autoimmune blistering disease. We previously showed that genetic variants within the ST18 gene promoter area confer a sixfold increase in the propensity to develop PV. ST18, a transcription factor, was found to be overexpressed in the epidermis of patients with PV. In addition, it was found to promote autoantibody-mediated abnormal epidermal cell-cell adhesion and secretion of proinflammatory mediators by keratinocytes.

OBJECTIVES

To delineate the mechanism through which ST18 contributes to destabilization of cell-cell adhesion.

METHODS

We used quantitative reverse-transcriptase polymerase chain reaction, immunofluorescence microscopy, a luciferase reporter system, site-directed mutagenesis, chromatin immunoprecipitation (ChIP) and the dispase dissociation assay.

RESULTS

The ChIP and luciferase reporter assays showed that ST18 directly binds and activates the TNF promoter. Accordingly, increased ST18 expression contributes to PV pathogenesis by destabilizing cell-cell adhesion in a tumour necrosis factor (TNF)-α-dependent fashion. In addition, dual immunofluorescence staining showed increased expression of both ST18 and TNF-α in the skin of patients with PV carrying an ST18-associated PV risk variant, which was found to be associated with a more extensive PV phenotype.

CONCLUSIONS

Our findings suggest a role for TNF-α in mediating the deleterious effect of increased ST18 expression in PV skin.

Autoreactive T cells in pemphigus: perpetrator and target

Pemphigus vulgaris (PV) is an autoimmune blistering disease, in which autoantibodies against epidermal cadherins, such as desmoglein (Dsg)1 and Dsg3, lead to the development of blisters and erosions on the skin and mucous membranes. Autoreactive CD4+ T cells are essential for the induction and perpetuation of the disease by interaction with B cells producing autoantibodies. PV has a strong genetic association with certain human leucocyte antigen (HLA) alleles with HLA-DRB1*04:02 and LA-DQB1*05:03 being the most prevalent in patients. Recently, genome-wide association studies have provided a new approach to identify single nucleotide polymorphisms, alongside the known association with HLA alleles. Loss of tolerance against Dsgs and other autoantigens is a critical event in the pathogenesis of PV. Epitope spreading contributes to the progression of PV, leading to an extension of the Dsg-specific autoimmune response to other molecular epitopes of autoantigens, such as desmocollins or muscarinic receptors. Alterations in CD4+CD25+ FoxP3+ regulatory T cells are thought to contribute to the development of PV representing a suitable target for therapeutic interventions. Several CD4+ T-cell subsets and cytokines are involved in the pathogenesis of PV, while Th2 cells are the extensively studied population. Recently, other T cell subsets like T follicular helper cells and Th17 have gained attention as new potential players in PV pathogenesis. The involvement of local autoantibody production in the lesional skin of PV patients in tertiary lymphoid organs is currently discussed but not yet clarified. In this study, we reviewed the current knowledge about the development, characteristics and function of autoreactive T cells in pemphigus and present current new T cell-targeted therapeutic approaches.

Beyond the HLA polymorphism: A complex pattern of genetic susceptibility to pemphigus

Pemphigus is a group of autoimmune bullous skin diseases that result in significant morbidity. As for other multifactorial autoimmune disorders, environmental factors may trigger the disease in genetically susceptible individuals. The goals of this review are to summarize the state of knowledge about the genetic variation that may affect the susceptibility and pathogenesis of pemphigus vulgaris and pemphigus foliaceus – both the endemic and the sporadic forms –, to compare and discuss the possible meaning of the associations reported, and to propose recommendations for new research initiatives. Understanding how genetic variants translate into pathogenic mechanisms and phenotypes remains a mystery for most of the polymorphisms that contribute to disease susceptibility. However, genetic studies provide a strong foundation for further developments in this field by generating testable hypotheses. Currently, results still have limited influence on disease prevention and prognosis, drug development, and clinical practice, although the perspectives for future applications for the benefit of patients are encouraging. Recommendations for the continued advancement of our understanding as to the impact of genetic variation on pemphigus include these partially overlapping goals: (1) Querying the functional effect of genetic variants on the regulation of gene expression through their impact on the nucleotide sequence of cis regulatory DNA elements such as promoters and enhancers, the splicing of RNA, the structure of regulatory RNAs and proteins, binding of these regulatory molecules to regulatory DNA elements, and alteration of epigenetic marks; (2) identifying key cell types and cell states that are implicated in pemphigus pathogenesis and explore their functional genomes; (3) integrating structural and functional genomics data; (4) performing disease-progression longitudinal studies to disclose the causal relationships between genetic and epigenetic variation and intermediate disease phenotypes; (5) understanding the influence of genetic and epigenetic variation in the response to treatment and the severity of the disease; (6) exploring gene-gene and genotype-environment interactions; (7) developing improved pemphigus-prone and non-prone animal models that are appropriate for research about the mechanisms that link genotypes to pemphigus. Achieving these goals will demand larger samples of patients and controls and multisite collaborations.

Genetics and Omics Analysis of Autoimmune Skin Blistering Diseases

Autoimmune blistering diseases (AIBDs) of the skin are characterized by autoantibodies against different intra-/extracellular structures within the epidermis and at the basement membrane zone (BMZ). Binding of the antibodies to their target antigen leads to inflammation at the respective binding site and degradation of these structures, resulting in the separation of the affected skin layers. Clinically, blistering, erythema and lesions of the skin and/or mucous membranes can be observed. Based on the localization of the autoantigen, AIBDs can be divided into pemphigus (intra-epidermal blistering diseases) and pemphigoid diseases (sub-epidermal blistering diseases), respectively. Although autoantigens have been extensively characterized, the underlying causes that trigger the diseases are still poorly understood. Besides the environment, genetic factors seem to play an important role in a predisposition to AIBDs. Here, we review currently known genetic and immunological mechanisms that contribute to the pathogenesis of AIBDs. Among the most commonly encountered genetic predispositions for AIBDs are the HLA gene region, and deleterious mutations of key genes for the immune system. Particularly, HLA class II genes such as the HLA-DR and HLA-DQ alleles have been shown to be prevalent in patients. This has prompted further epidemiological studies as well as unbiased Omics approaches on the transcriptome, microbiome, and proteome level to elucidate common and individual genetic risk factors as well as the molecular pathways that lead to the pathogenesis of AIBDs.

Pemphigus

Pemphigus consists of a group of rare and severe autoimmune blistering diseases mediated by pathogenic autoantibodies mainly directed against two desmosomal adhesion proteins, desmoglein (Dsg)1 and Dsg3 (also known as DG1 and DG3), which are present in the skin and surface-close mucosae. The binding of autoantibodies to Dsg proteins induces a separation of neighbouring keratinocytes, in a process known as acantholysis. The two main pemphigus variants are pemphigus vulgaris, which often originates with painful oral erosions, and pemphigus foliaceus, which is characterised by exclusive skin lesions. Pemphigus is diagnosed on the basis of either IgG or complement component 3 deposits (or both) at the keratinocyte cell membrane, detected by direct immunofluorescence microscopy of a perilesional biopsy, with serum anti-Dsg1 or anti-Dsg3 antibodies (or both) detected by ELISA. Corticosteroids are the therapeutic mainstay, which have recently been complemented by the anti-CD20 antibody rituximab in moderate and severe disease. Rituximab induces complete remission off therapy in 90% of patients, despite rapid tapering of corticosteroids, thus allowing for a major corticosteroid-sparing effect and a halved number of adverse events related to corticosteroids.

Single-nucleotide polymorphisms associated with pemphigus vulgaris: Potent markers for better treatment and personalized medicine

Pemphigus vulgaris (PV) is a rare autoimmune blistering disorder, which could affect both skin and mucosal surfaces. There is increasing evidence that genetics plays a critical role in PV development, severity and prognosis. Single-nucleotide polymorphisms (SNPs) are the most common type of genetic variation among people and have been widely evaluated in most diseases. However, there are few studies regarding the roles of SNPs in the PV. Here, we reviewed both pathogenic and protective roles of the SNPs in non-HLA genes regarding the PV. Among the large number of studied SNPs, it was found that several SNPs in different genes might control the susceptibility of PV, including TNFA (rs361525, rs1800629, rs1800629), IL10 (rs1800871, rs1800896, rs1800871, and rs1800872), IL6 (rs1800795), CTLA4 (rs231775), ICOS (rs10932029), CD86 (rs1129055), DSG3 (rs8085532, rs3911655, rs3848485, rs3794925, rs1466379), ST18 (rs2304365, rs17315309) and TAP2 (rs7454108), probably in a population-specific manner. Moreover, SNPs in glucocorticoid receptor, also known as nuclear receptor subfamily 3 group C member 1 (NR3C1) gene, including rs11745958, rs17209237, rs33388, rs7701443 as well as rs116855232 at NUDT15, seem to be associated with therapeutic outcomes in PV patients. Additionally, variations in the other genes involved in the drugs' metabolisms, pharmacokinetics and pharmacodynamics such as rs396991 in FCGR3A gene could be used for the prediction of clinical response to drugs and side effects. Taken together, SNPs seem to be valuable tools for better management of PV patients. Further studies need to be conducted to evaluate SNPs in genes that control immune responses and apoptosis.