Assessing ST18 gene polymorphisms (rs17315309, rs2304365) in Iraqi patients with Pemphigus vulgaris.

Pemphigus vulgaris (PV) is a potentially fatal autoimmune disease characterized by blistering of the skin, mucous membranes, and oral cavity. Genetics are implicated in its etiology, with the ST18 gene identified as a potential risk factor for pemphigus in certain populations, suggesting its role as a novel molecular target for therapeutic intervention. This study aimed to detect single nucleotide polymorphisms (SNPs) rs17315309 A/G and rs2304365 C/G in the ST18 gene among Iraqi/Arabic patients with PV. A total of 90 Iraqi subjects participated in this study, including 45 patients diagnosed with PV and 45 healthy controls. SNP analysis was performed using High-Resolution Melt Analysis (HRMA) with Eva Green I Dye. For SNP rs17315309 A/G, the distribution of heterozygous genotypes showed highly significant differences between the patient and healthy groups (P = 0.005), with the mutant G-allele being significantly more prevalent in patients than in the healthy group (P = 0.001). In contrast, for SNP rs2304365 C/G, the distribution of heterozygous and mutant genotypes did not differ significantly between patients and healthy individuals (P = 0.8 and P = 0.3, respectively), with the mutant G-allele also showing no significant difference (P = 0.4). Our data indicate a significant association between PV and the rs17315309 A/G SNP in the ST18 gene among the Iraqi population of Arabic origin. However, no association was found between patients with PV and the rs2304365 C/G SNP in the same gene.

Whole-Exome Sequencing Reveals the Genomic Profile and IL6ST Variants as a Prognostic Biomarker of Paraneoplastic Pemphigus-Associated Unicentric Castleman Disease.

Unicentric Castleman disease (UCD) is a rare lymphoproliferative disorder. Paraneoplastic pemphigus (PNP) is a major complication associated with poor UCD prognosis. However, the genomic profiles and prognostic biomarkers of PNP-associated UCD remain unclear. In this study, we performed whole-exome sequencing analysis for 28 matched tumor-normal pairs and 9 tumor-only samples to define the genomic landscape of Chinese patients with PNP-associated UCD. An integrative analysis was performed to identify somatic variants, the mutational signatures, and key pathways in tumors. Besides, we analyzed the relationship among mutated genes, clinical characteristics, and prognosis. Sixty-one somatic mutant genes were identified in >1 patient with PNP-associated UCD. Specifically, IL6ST and PDGFRB were the most frequently mutated genes (32%), followed by DPP6 (18%) and MUC4 (18%). Signaling molecules and interactions, cellular processes, and signal transduction pathways were enriched. Furthermore, we found that poor overall survival was related to IL6ST variants (P = .02). Finally, we classified PNP-associated UCD into 4 genomic subgroups: IL6ST, PDGFRB, IL6ST-PDGFRB, and an unknown subgroup. In summary, we defined the molecular profile of PNP-associated UCD and identified a potential molecular biomarker for predicting prognosis, which may provide therapeutic targets for treating this severe disorder.

Single-Cell Transcriptomes and Immune Repertoires Reveal the Cell State and Molecular Changes in Pemphigus Vulgaris.

The etiology and pathogenesis of pemphigus vulgaris (PV) entail intricate interactions between immune cells and epithelial cells. However, the specific subtypes of immune cells involved in PV, along with their respective roles, remain elusive. Likewise, the precise functions and mechanisms by which glucocorticoids affect cell types within the disease context require further elucidation. To address these knowledge gaps, we performed 5' single-cell RNA sequencing, combined with V(D)J enrichment on buccal mucosal lesions and peripheral blood samples from treatment-naive patients with PV, in conjunction with post-treatment peripheral blood samples obtained after oral prednisone treatment. Our findings suggest that the IL-1α signaling pathway, myeloid APCs, inflammatory CD8+ resident memory T cells, and dysfunctional CD4+ regulatory T cells are involved in the pathogenesis of PV. Part of these findings were validated by immunohistochemical assays and multiplex immunofluorescence assays. Furthermore, our results highlight the significant impact of prednisone treatment on monocytes and mucosal-associated invariant T cells while revealing a limited effect on CD4+ regulatory T cells. Additionally, we present the CDR3 amino acid sequence of BCR related to PV disease and investigate the characteristics of TCR/BCR clonotypes. In conclusion, our study provides a comprehensive understanding of PV, particularly focusing on the mucosal-dominant type, and sheds light on the effects of glucocorticoids within the PV context. These insights hold promise for the development of new therapeutic strategies in this autoimmune disorder.

Role of Human Leukocyte Antigen Class II in Antibody-Mediated Skin Disorders.

HLA class II molecules are key factors determining susceptibility to autoimmune disorders, and their role in immune-mediated skin conditions such as psoriasis has been extensively investigated. However, there is currently little understanding of their role in antibody-mediated skin diseases such as autoimmune blistering disorders. We researched the available literature using PubMed to narratively review the current knowledge on HLA associations in antibody-mediated blistering skin pathologies. Our results summarized the risk alleles that are identified in the literature, together with certain known protective alleles: in the pemphigus group, alleles HLA-DQB1*0503 and HLA-DRB1*0402 are most commonly associated with disease; in the pemphigoid group, the most studied allele is HLA-DQB1*0301; in epidermolysis bullosa acquisita, few genetic studies are available; in dermatitis herpetiformis, the association with haplotypes HLA-DQ2 and HLA-DQ8 is strongly established; finally, in linear IgA bullous disease, specific HLA alleles may be responsible for pediatric presentations. Our current pathogenic understanding of this group of disorders assigns a key role to predisposing HLA class II alleles that are able to bind disease autoantigens and therefore stimulate antigen-specific autoreactive T cells. The latter engage B lymphocytes that will produce pathogenic autoantibodies. The distribution of HLA alleles and their disease associations are variable across demographics, and an in-depth pathogenetic understanding is needed to support associations between HLA alleles and disease phenotypes. Additionally, in a personalized medicine approach, the identification of HLA alleles associated with the risk of disease may become clinically relevant in identifying susceptible subjects that should avoid exposure to known triggers, such as medication, when possible.

Plasma Exosomal microRNA Profile Reveals miRNA 148a-3p Downregulation in the Mucosal-Dominant Variant of Pemphigus Vulgaris.

The mucosal-dominant variant of pemphigus vulgaris (MPV) is an autoimmune disease characterized by oral mucosal blistering and circulating pathogenic IgG antibodies against desmoglein 3 (Dsg3), resulting in life-threatening bullae and erosion formation. Recently, microRNAs (miRNAs) have emerged as promising players in the diagnosis and prognosis of several pathological states. For the first time, we have identified a different expression profile of miRNAs isolated from plasma-derived exosomes (P-EVs) of MPV patients positive for antibodies against Dsg3 (Dsg3-positive) compared to healthy controls. Moreover, a dysregulated miRNA profile was confirmed in MPV tissue biopsies. In particular, a strong downregulation of the miR-148a-3p expression level in P-EVs of MPV patients compared to healthy controls was demonstrated. Bioinformatics prediction analysis identifies metalloproteinase-7 (MMP7) as a potential miR-148a-3p target. An in vitro acantholysis model revealed that the miR-148a-3p expression level was dramatically downregulated after treatment with Dsg3 autoantibodies, with a concomitant increase in MMP7 expression. The increased expression of MMP7 leads to the disruption of intercellular and/or extracellular matrix adhesion in an in vitro cellular model of MPV, with subsequent cell dissociation. Overexpression of miR-148a-3p prevented cell dissociation and regressed MMP7 upregulation. Our findings suggest a pivotal role of P-EV cargo in regulating molecular mechanisms involved in MPV pathogenesis and indicate them as potential MPV therapeutic targets.

Worldwide epidemiologic factors in pemphigus vulgaris and bullous pemphigoid.

Autoimmune blistering diseases such as bullous pemphigoid (BP) and pemphigus vulgaris (PV) are complex, multifactorial, and polygenic diseases, whose exact pathogenesis is difficult to pinpoint. Research aimed at elucidating the associated epidemiologic risk factors of these two diseases has been hampered by their rare disease status. Further, a lack of centralization and standardization of available data makes the practical application of this information challenging. In order to collate and clarify the available literature we comprehensively reviewed 61 PV articles from 37 different countries and 35 BP articles from 16 different countries addressing a range of disease relevant clinical parameters including age of onset, sex, incidence, prevalence, and HLA allele association. The reported incidence of PV ranged from 0.098 to 5 patients per 100,000 people, while BP ranged from 0.21 to 7.63 patients per 100,000. Prevalence of PV ranged from 0.38 to 30 per 100,000 people and BP ranged from 1.46 to 47.99 per 100,000. The mean age of onset in patients ranged from 36.5 to 71 years for PV and 64 to 82.6 years for BP. Female-to-male ratios ranged from 0.46 to 4.4 in PV and 1.01 to 5.1 in BP. Our analysis provides support for the reported linkage disequilibrium of HLA DRB1*0402 (an allele previously shown to be associated with PV) and DQB1*0302 alleles in Europe, North America, and South America. Our data also highlight that HLA DQB1*0503 (also known to be associated with PV) appears in linkage disequilibrium with DRB1*1404 and DRB1*1401, mainly in Europe, the Middle East, and Asian countries. The HLA DRB1*0804 allele was only associated with PV in patients of Brazilian and Egyptian descent. Only two HLA alleles were reported as associated with BP more than twice in our review, DQB1*0301 and DQA1*0505. Collectively, our findings provide detailed insights into the variation of disease parameters relevant to PV and BP that can be expected to inform future work aimed at unraveling the complex pathogenesis of these conditions across the globe.

miRNA implication in the pathogenesis and the outcome of Tunisian endemic pemphigus foliaceus.

Pemphigus foliaceus (PF) is a bullous autoimmune skin disease diagnosed through sera and skin analyses. PF severity is associated with maintained anti-Dsg1 sera levels and its prognosis is unpredictable. MicroRNA (miRNA), dynamic regulators of immune function, have been identified as potential biomarkers for some autoimmune diseases. This study aimed to assess the miRNA expression of miR-17-5p, miR-21-5p, miR-146a-5p, miR-155-5p and miR-338-3p using quantitative real-time PCR in peripheral blood mononuclear cells (PBMC) and lesional skin samples from untreated and treated PF patients (both remittent and chronic) over 3 months. Overall, miRNA expression was significantly higher in PBMC than in biopsy samples. Blood miR-21 expression was increased in untreated patients compared to controls and had a diagnostic value with an AUC of 0.78. After 6 weeks, it decreased significantly, similar to anti-Dsg1 antibodies and the PDAI score. In addition, a positive correlation was observed between cutaneous miR-21 expression and the disease activity score. Conversely, cutaneous expressions of miR-17, miR-146a and miR-155 were significantly higher in treated chronic patients compared to remittent ones. The cutaneous level of miR-155 positively correlated with pemphigus activity, making it a potential predictive marker for patients' clinical stratification with an AUC of 0.86.These findings suggest that blood miR-21 and cutaneous miR-155 can be used as supplemental markers for PF diagnosis and activity, respectively in addition to classical parameters.

Anti-desmoglein 1 antibody-positive mother and antibody-negative child with Darier's disease.

We report a mother and an adult son with Darier's disease. The mother, 76 years old and Japanese, had positivity for anti-desmoglein (Dsg)1 antibodies. She had erythema with hyperkeratosis and seborrheic and interstitial blistering. A high level of anti-Dsg1 antibodies was detected in the serum. Histopathological examination showed acantholysis and direct immunofluorescence testing revealed intercellular IgG and C3 deposition of the epidermis. Although she was diagnosed as having pemphigus foliaceus, the skin lesions slightly improved with immunosuppressive therapy. Her son, 47 years old, had similar skin lesions on the seborrheic and interstitial parts, but the anti-Dsg1 antibodies were negative in his serum. Histopathological examination showed acantholysis and dyskeratotic cells. Although Hailey-Hailey disease was first suspected, no mutation in the ATP2C1 was detected in either patient. Trio-exome analysis including the father showed a heterozygous c.2027C>A transition on exon 14 of ATP2A2, causing a replacement at amino acid 676 (p.Ala676Asp) in the mother and son only. The two patients were then diagnosed as having Darier's disease. Exome analysis further showed that a novel heterozygous missense mutation of DSG1 was identified only in the affected mother. Anti-Dsg1 antibody-positive Darier's disease is reported here for the first time. Very rare coexistence of Darier's disease and anti-Dsg1 antibody-positivity might be associated with this novel heterozygous DSG1 mutation. Experimental evidence is required to validate this hypothesis.

Evaluation of X chromosome inactivation in endemic Tunisian pemphigus foliaceus.

BACKGROUND: Almost 5% of the world's population develops an autoimmune disease (AID), it is considered the fourth leading cause of disability for women, who represent 78% of cases. The sex ratio when it comes to the most prevalent AID varies from 9:1 in systemic lupus erythematosus (SLE) to 13:1 in endemic Tunisian pemphigus foliaceus (PF). METHODS: To test the potential involvement of skewed x-inactivation in the pathogenesis of Tunisian PF, we analyzed the methylation status of a highly polymorphic CAG repeat in the androgen receptor gene and evaluated the x chromosome inactivation (XCI) patterns in peripheral blood-leukocyte-derived DNA samples of female patients with PF (n = 98) compared to healthy control (HC) subjects (n = 150), as well as female patients with SLE (n = 98) were enrolled as a reference group. RESULTS: XCI status was informative for 50 of the 98 PF patients (51%) and 70 of the 150 HC women (47%). Extremely skewed XCI patterns were more frequent in PF and SLEwomen than HC, but the difference was statistically significant only in women with SLE. No statistical difference was observed in XCI patterns between PF and SLE patients. PF phenotype-XCI correlation analysis revealed that (i) skewed XCI patterns may be involved in the disease's subtype and (ii) it was more pronounced in the endemic group than the sporadic one. Furthermore, preferential XCI showed an increase in heterozygote genotypes of PF's susceptibility polymorphisms in immunity-related X genes (FOXP3, AR, and TLR7) in PF patients compared to HC. CONCLUSION: Our results suggest that skewed XCI could lead to hemizygosity of X-linked alleles that might unmask X-linked deleterious alleles.

Association of specific HLA alleles and haplotypes with pemphigus vulgaris in the Bulgarian population.

Pemphigus vulgaris (PV) is an autoimmune bullous dermatosis with uneven geographic distribution and higher incidence in certain populations. In previous studies, a relatively high incidence of PV was reported in Bulgaria (0.47/100,000/year) comparable to that in other countries. The genetic background was considered responsible for the disease susceptibility, and multiple reports have proven PV to be an HLA-associated condition. The aim of our study was to analyze the role of genetic factors in the development of PV in Bulgaria. HLA genotyping was performed in 56 PV patients, ethnic Bulgarians whose diagnosis was confirmed based on clinical, histological, and immunofluorescent findings. The control group consisted of 204 healthy individuals from the Bulgarian population without evidence for HLA-associated autoimmune diseases. HLA-A,-B,-DRB1,-DQB1 analysis was performed by PCR-SSP. Our results revealed predisposing associations with DRB1*14, DRB1*04:02, and B*38, B*55, while allele DRB1*03:01 and the corresponding haplotypes were significantly decreased in the PV patients. The predisposing role of these alleles has been observed in other populations. All reported predisposing DRB1 alleles have the same amino acids at key positions of the beta chain of the HLA molecules, 26 (Phe), 67 (Leu or Ileu), 70 and 71 (hydrophobic AA: Gln, Arg, Asp, or Glu), and 86 (Val), which is important for the selective presentation of desmoglein 3 peptides. Additionally, specific alleles HLA-A*01 and DRB1*11 were identified with decreased frequencies in the patients' group, the last one being a common protective allele for autoimmune diseases in the Bulgarian population. The elucidation of the role of genetic factors for the development of pemphigus will help explain its higher incidence and clinical variability in certain populations.

A systematic review and meta-analysis of HLA class II associations in patients with IgG4 autoimmunity.

Autoimmune diseases caused by pathogenic IgG4 subclass autoantibodies (IgG4-AID) include diseases like MuSK myasthenia gravis, pemphigus vulgaris or thrombotic thrombocytopenic purpura. Their etiology is still unknown. Polymorphisms in the human leukocyte antigen (HLA) gene locus, particularly in HLA-DRB1, are known genetic susceptibility factors for autoimmune diseases. We hypothesized a similar role for HLA polymorphisms in IgG4-AID and conducted a systematic review and meta-analysis with case-control studies on IgG4-AID based on MOOSE/ HuGENet guidelines. Genotype (G) and allele (A) frequencies of HLA-DQB1*05 (G: OR 3.8; 95% CI 2.44-5.9; p < 0.00001; A: OR 2.54; 95% CI 1.82-3.55; p < 0.00001) and HLA-DRB1*14 (G: OR 4.31; 95% CI 2.82-6.59; p < 0.00001; A: OR 4.78; 95% CI 3.52-6.49; p < 0.00001) and the HLA-DRB1*14-DQB1*05 haplotype (OR 6.3; 95% CI 3.28-12.09; p < 0.00001/OR 4.98; 95% CI 3.8-6.53; p < 0.00001) were increased while HLA-DRB1*13 (G: OR 0.48; 95% CI 0.34-0.68; p < 0.0001; A: OR 0.46; 95% CI 0.34-0.62; p < 0.00001) was decreased in IgG4-AID patients. In conclusion, the HLA-DQB1*05, HLA-DRB1*14 alleles and the HLA-DQB1*05-DRB1*14 haplotype could be genetic risk factors that predispose for the production of pathogenic IgG4 autoantibodies and the HLA-DRB1*13 allele may protect from IgG4 autoimmunity.

Genetic Associations and Differential mRNA Expression Levels of Host Genes Suggest a Viral Trigger for Endemic Pemphigus Foliaceus.

The long search for the environmental trigger of the endemic pemphigus foliaceus (EPF, fogo selvagem) has not yet resulted in any tangible findings. Here, we searched for genetic associations and the differential expression of host genes involved in early viral infections and innate antiviral defense. Genetic variants could alter the structure, expression sites, or levels of the gene products, impacting their functions. By analyzing 3063 variants of 166 candidate genes in 227 EPF patients and 194 controls, we found 12 variants within 11 genes associated with differential susceptibility (p < 0.005) to EPF. The products of genes TRIM5, TPCN2, EIF4E, EIF4E3, NUP37, NUP50, NUP88, TPR, USP15, IRF8, and JAK1 are involved in different mechanisms of viral control, for example, the regulation of viral entry into the host cell or recognition of viral nucleic acids and proteins. Only two of nine variants were also associated in an independent German cohort of sporadic PF (75 patients, 150 controls), aligning with our hypothesis that antiviral host genes play a major role in EPF due to a specific virus−human interaction in the endemic region. Moreover, CCL5, P4HB, and APOBEC3G mRNA levels were increased (p < 0.001) in CD4+ T lymphocytes of EPF patients. Because there is limited or no evidence that these genes are involved in autoimmunity, their crucial role in antiviral responses and the associations that we observed support the hypothesis of a viral trigger for EPF, presumably a still unnoticed flavivirus. This work opens new frontiers in searching for the trigger of EPF, with the potential to advance translational research that aims for disease prevention and treatment.

Transcriptomic profiling of pemphigus lesion infiltrating mononuclear cells reveals a distinct local immune microenvironment and novel lncRNA regulators.

Pemphigus is an autoimmune skin disease. Ectopic lymphoid-like structures (ELSs) were found to be commonly present in the pemphigus lesions, presumably supporting in situ desmoglein (Dsg)-specific antibody production. Yet functional phenotypes and the regulators of Lymphoid aggregates in pemphigus lesions remain largely unknown. Herein, we used microarray technology to profile the gene expression in skin lesion infiltrating mononuclear cells (SIMC) from pemphigus patients. On top of that, we compared SIMC dataset to peripheral blood mononuclear cells (PBMC) dataset to characterize the unique role of SIMC. Functional enrichment results showed that mononuclear cells in skin lesions and peripheral blood both had over-represented IL-17 signaling pathways while neither was characterized by an activation of type I Interferon signaling pathways. Cell-type identification with relative subsets of known RNA transcripts (CIBERSORT) results showed that naïve natural killer cells (NK cells) were significantly more abundant in pemphigus lesions, and their relative abundance positively correlated with B cells abundance. Meanwhile, plasma cells population highly correlated with type 1 macrophages (M1) abundance. In addition, we also identified a lncRNA LINC01588 which might epigenetically regulate T helper 17 cells (Th17)/regulatory T cells (Treg) balance via the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Here, we provide the first transcriptomic characterization of lesion infiltrating immune cells which illustrates a distinct interplay network between adaptive and innate immune cells. It helps discover new regulators of local immune response, which potentially will provide a novel path forward to further uncover pemphigus pathological mechanisms and develop targeted therapy.

Allele frequency and the associations of HLA-DRB1 and HLA-DQB1 polymorphisms with pemphigus subtypes and disease severity.

ABSTRACT: Pemphigus is a rare, devastating, bullous autoimmune disease that damages the skin and mucous membranes, and has high morbidity and mortality. Studies have shown associations of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) with human leukocyte antigen (HLA) class II polymorphisms.This study examined the frequency of Major Histocompatibility Complex, Class II, DR Beta 1, a Protein Coding gene (HLA-DRB1) and Major Histocompatibility Complex, Class II, DQ Beta 1 (HLA-DQB1) alleles in Vietnamese PV and PF patients, and the association of these polymorphisms with pemphigus subtypes and disease severity.The study enrolled 31 unrelated Vietnamese who underwent HLA typing using Sanger sequencing.HLA-DRB1∗14:54 was the most frequent allele in both PV (20.5%) and PF (33.3%) patients. The percentage of HLA-DQB1∗03:02 was significantly higher in PF than PV patients, while the percentage of HLA-DQB1∗05:03 was approximately 10 times higher in PV patients. Pemphigus patients who have the HLA-DRB1∗04 alleles are more likely to have mild or moderate disease.The HLA-DRB1 and DQB1 alleles may influence susceptibility to pemphigus subtypes, with DQB1∗05:03 being specific for PV and DQB1∗03:02 for PF. Our findings suggest that the DRB1∗04 alleles are likely to be associated with mild and moderate disease.

Up-regulation of ST18 in pemphigus vulgaris drives a self-amplifying p53-dependent pathomechanism resulting in decreased desmoglein 3 expression.

Pemphigus vulgaris (PV) is a life-threatening autoimmune mucocutaneous blistering disease which is to a large extent genetically determined, and results, at least in part, from the deleterious activity of autoantibodies directed against desmoglein (DSG)3, a prominent intra-epidermal adhesion molecule. Those autoantibodies lead to decreased membranal DSG3 expression in keratinocytes (KCs), thereby destabilizing cell-cell adhesion within the epidermis and leading to blister formation. We previously showed that rs17315309, a strong risk variant for PV within the promoter of the ST18 transcription factor gene, promotes epidermal ST18 up-regulation in a p53/p63-dependent manner. Accordingly, ST18 was found to be overexpressed in the skin of PV patients. Increased ST18 expression was then shown to markedly augment PV autoantibodies-mediated loss of KCs cohesion. Here, we demonstrate that ST18 overexpression significantly increases autoantibody-mediated DSG3 down-regulation in keratinocytes. In addition, DSG3 decreased expression boosts p53 function through p38 mitogen-activated protein kinase (p38MAPK) activation and dramatically augments p53-dependent ST18 promoter activity. Finally, the PV risk variant rs17315309 is associated with increased p53 expression in PV skin. Taken collectively, these observations reveal a novel self-amplifying pathomechanism involving ST18, DSG3, p38 and p53, capable of perpetuating disease activity, and therefore indicative of novel actionable molecular targets in PV.

The Immunogenetics of Autoimmune Blistering Diseases.

Dermatological conditions constituting the group of autoimmune blistering diseases (AIBD) are characterized by loss of immunotolerance and humoral, as well as cellular, autoimmune responses that result in the development of bullae and erosions on the skin and mucous membranes. AIBDs are broadly categorized into pemphigus and pemphigoid classes with several distinct subtypes amongst them. Advances in genetics have allowed for the study and identification of alleles, and even single nucleotide polymorphisms, that harbor increased susceptibility or confer protection for the development of these conditions. The focus of this chapter pertains to a comprehensive review of the known genetic associations with AIBDs, including HLA class I-III, as well as non-HLA genes and non-coding sequences that influence cellular processes and signaling pathways.

IgM to IgG Class Switching Is a Necessary Step for Pemphigus Phenotype Induction in Desmoglein 3-Specific B Cell Receptor Knock-in Mouse.

Pemphigus vulgaris is an autoimmune blistering disease caused by IgG targeting desmoglein 3 (Dsg3), an adhesion molecule of keratinocytes. Anti-Dsg3 IgG production is prevented in healthy individuals, but it is unclear how Dsg3-specific B cells are regulated. To clarify the immunological condition regulating Dsg3-specific B cells, a pathogenic anti-Dsg3 Ig (AK23) knock-in mouse was generated. AK23 knock-in B cells developed normally without undergoing deletion or acquiring an anergic phenotype in vivo. The knock-in B cells showed Ca2+ influx upon IgM cross-linking and differentiated into AK23-IgG+ B cells after LPS and IL-4 stimulation in vitro that induced a pemphigus phenotype after adoptive transfer into Rag2 -/- mice. However, the knock-in mouse itself produced AK23-IgM but little IgG without blisters in vivo. Dsg3 immunization and skin inflammation caused AK23-IgG production and a pemphigus phenotype in vivo. Furthermore, Fcgr2b deficiency or haploinsufficiency spontaneously induced AK23-IgG production and a pemphigus phenotype with poor survival rates in AK23 knock-in mice. To assess Fcgr2b involvement in Ig class-switch efficiency, postswitch transcripts of B cells were quantified and significantly higher in Fcgr2b -/- and Fcgr2b +/- mice than wild-type mice in a gene dose-dependent manner. Finally, RNA sequencing revealed reduced expression of FCGR2B and FcγRIIB-related genes in patient B cells. These results indicated that Dsg3-specific B cells do not spontaneously perform pathogenic class switching in vivo, and pemphigus phenotype induction was prevented under normal conditions. Attenuated FcγRIIB signaling is also one of the drivers for pathogenic class switching and is consistent with immunological features identified from clinical samples. This study unveiled a characteristic immune state silencing autoreactive B cells in mice.

Translational implications of Th17-skewed inflammation due to genetic deficiency of a cadherin stress sensor.

Desmoglein 1 (Dsg1) is a cadherin restricted to stratified tissues of terrestrial vertebrates, which serve as essential physical and immune barriers. Dsg1 loss-of-function mutations in humans result in skin lesions and multiple allergies, and isolated patient keratinocytes exhibit increased proallergic cytokine expression. However, the mechanism by which genetic deficiency of Dsg1 causes chronic inflammation is unknown. To determine the systemic response to Dsg1 loss, we deleted the 3 tandem Dsg1 genes in mice. Whole transcriptome analysis of embryonic Dsg1-/- skin showed a delay in expression of adhesion/differentiation/keratinization genes at E17.5, a subset of which recovered or increased by E18.5. Comparing epidermal transcriptomes from Dsg1-deficient mice and humans revealed a shared IL-17-skewed inflammatory signature. Although the impaired intercellular adhesion observed in Dsg1-/- mice resembles that resulting from anti-Dsg1 pemphigus foliaceus antibodies, pemphigus skin lesions exhibit a weaker IL-17 signature. Consistent with the clinical importance of these findings, treatment of 2 Dsg1-deficient patients with an IL-12/IL-23 antagonist originally developed for psoriasis resulted in improvement of skin lesions. Thus, beyond impairing the physical barrier, loss of Dsg1 function through gene mutation results in a psoriatic-like inflammatory signature before birth, and treatment with a targeted therapy significantly improved skin lesions in patients.