Immunogenetics of pemphigus: An update

HLA class II antigens in Croatian patients with pemphigus vulgaris and their correlation with anti-desmoglein antibodies

Pemphigus vulgaris (PV) is an acquired autoimmune blistering disease characterized by the production of autoantibodies targeting desmosomal cadherins, primarily desmoglein 1 and desmoglein 3, leading to acantholysis. The etiology of PV is multifactorial, including genetic susceptibility. This retrospective study aimed to evaluate the association of HLA class II alleles and PV and to examine the impact of PV-associated HLA class II alleles on the concentration of anti-desmoglein antibodies. The study group included 30 patients in whom the diagnosis of PV was confirmed by histopathological analysis, immunofluorescence findings, and ELISA testing for detecting antibodies against desmoglein 1 and desmoglein 3. HLA class II alleles were typed by polymerase chain reaction with sequence-specific primers (PCR-SSP). The control group consisted of 190 healthy volunteer blood donors. Data analysis revealed a significantly higher frequency of HLA class II alleles in our population of patients with PV, including HLA-DRB1*04:02, HLA-DRB1*14:54, HLA-DQB1*03:02, HLA-DQB1*05:03, HLA- DQA1*03:01, and HLA-DQA1*01:04, as well as a significantly lower frequency of HLA-DQA1*05:01 compared to the control group. We have also investigated the influence of risk alleles for PV, recognized in almost all study populations, HLA-DRB1*04:02 and HLA-DQB1*05:03, on the concentration of antibodies against desmogleins 1 and 3 in relation to the presence of these alleles. The results showed significantly higher levels of antibodies directed against desmoglein 3 among patients with DRB1*04:02 compared to patients without this allele. No difference was found for anti-desmoglein 1 antibodies. Regarding DQB1*05:03 allele, statistical analysis showed no differences in the concentration of anti-desmoglein antibodies in patients carrying this allele versus those without it.

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.

Oral Mucosal Injury Caused by Targeted Cancer Therapies

Targeted cancer therapies have fundamentally transformed the treatment of many types of cancers over the past decade, including breast, colorectal, lung, and pancreatic cancers, as well as lymphoma, leukemia, and multiple myeloma. The unique mechanisms of action of these agents have resulted in many patients experiencing enhanced tumor response together with a reduced adverse event profile as well. Toxicities do continue to occur, however, and in selected cases can be clinically challenging to manage. Of particular importance in the context of this monograph is that the pathobiology for oral mucosal lesions caused by targeted cancer therapies has only been preliminarily investigated. There is distinct need for novel basic, translational, and clinical research strategies to enhance design of preventive and therapeutic approaches for patients at risk for development of these lesions. The research modeling can be conceptually enhanced by extrapolating "lessons learned" from selected oral mucosal conditions in patients without cancer as well. This approach may permit determination of the extent to which pathobiology and clinical management are either similar to or uniquely distinct from oral mucosal lesions caused by targeted cancer therapies. Modeling associated with oral mucosal disease in non-oncology patients is thus presented in this context as well. This article addresses this emerging paradigm, with emphasis on current mechanistic modeling and clinical treatment. This approach is in turn designed to foster delineation of new research strategies, with the goal of enhancing cancer patient treatment in the future.

The association between ST18 gene polymorphism and severe pemphigus disease among Iranian population

Recently, ST18 polymorphism has played a role in increasing the risk of pemphigus among some populations such as Egyptian and Jewish. In addition, a variant within the ST18 promoter gene was shown to induce ST18 upregulation and cytokine secretion leading to keratinocyte susceptibility to anti-desmoglein antibodies. Thus, the present study aimed to assess the ST18 single nucleotide polymorphisms (SNP) relationship with pemphigus, disease severity and family history among Iranian population. A total of 111 pemphigus patients and 201 healthy controls were genotyped for three ST18 SNPs rs2304365, rs10504140 and rs4074067 by using TETRA-ARMS PCR method. The results indicated that risk allele A in rs2304365 was significantly higher in pemphigus patients, compared with the amount in the control group (OR = 2.43 CI = 1.49-3.975, P < 0.001). Thus, A allele represents a risk factor for pemphigus. Further, the patients carrying the risk allele had a more severe disease and a higher age of disease onset while no relationship was observed between the number of relapses and positive family history of pemphigus with the risk allele. Finally, dominant model was regarded as the strongest inheritance model for the associated risk. The present study confirmed the relationship between ST18 gene with pemphigus disease, a more severe disease, and a higher age of disease onset.

A reciprocal HLA-Disease Association in Rheumatoid Arthritis and Pemphigus Vulgaris

Human leukocyte antigens (HLA) have been extensively studied as being antigen presenting receptors, but many aspects of their function remain elusive, especially their association with various autoimmune diseases. Here we discuss an illustrative case of the reciprocal relationship between certain HLA-DRB1 alleles and two diseases, rheumatoid arthritis (RA) and pemphigus vulgaris (PV). RA is strongly associated with HLA-DRB1 alleles that encode a five amino acid sequence motif in the 70-74 region of the DR beta chain, called the shared epitope (SE), while PV is associated with the HLA-DRB1*04:02 allele that encodes a different sequence motif in the same region. Interestingly, while HLA-DRB1*04:02 confers susceptibility to PV, this and other alleles that encode the same sequence motif in the 70-74 region of the DR beta chain are protective against RA. Currently, no convincing explanation for this antagonistic effect is present. Here we briefly review the immunology and immunogenetics of both diseases, identify remaining gaps in our understanding of their association with HLA, and propose the possibility that the 70-74 DR beta epitope may contribute to disease risk by mechanisms other than antigen presentation.

Induction of T regulatory cells by the superagonistic anti-CD28 antibody D665 leads to decreased pathogenic IgG autoantibodies against desmoglein 3 in a HLA-transgenic mouse model of pemphigus vulgaris

Pemphigus vulgaris (PV) is a potentially life-threatening autoimmune disease of the skin and mucous membranes. Its pathogenesis is based on IgG autoantibodies that target the desmosomal cadherins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1) and induce intra-epidermal loss of adhesion. Although the PV pathogenesis is well-understood, therapeutic options are still limited to immunosuppressive drugs, particularly corticosteroids, which are associated with significant side effects. Dsg3-reactive T regulatory cells (Treg) have been previously identified in PV and healthy carriers of PV-associated HLA class II alleles. Ex vivo, Dsg3-specific Treg cells down-regulated the activation of pathogenic Dsg3-specific T-helper (Th) 2 cells. In this study, in a HLA-DRB1*04:02 transgenic mouse model of PV, peripheral Treg cells were modulated by the use of Treg-depleting or expanding monoclonal antibodies, respectively. Our findings show that, in vivo, although not statistically significant, Treg cells exert a clear down-regulatory effect on the Dsg3-driven T-cell response and, accordingly, the formation of Dsg3-specific IgG antibodies. These observations confirm the powerful immune regulatory functions of Treg cells and identify Treg cells as potential therapeutic modulators in PV.

Pathogenic IgG antibodies against desmoglein 3 in pemphigus vulgaris are regulated by HLA-DRB1*04:02-restricted T cells

Pemphigus vulgaris (PV) is considered as a model for an autoantibody-mediated organ-specific autoimmune disorder. IgG autoantibodies directed against the desmosomal cadherin desmoglein 3 (Dsg3), the major autoantigen in PV, cause loss of epidermal keratinocyte adhesion, resulting in blisters and erosions of the skin and mucous membranes. The association of human autoimmune diseases with distinct HLA alleles is a well-known phenomenon, such as the association with HLA-DRB1*04:02 in PV. However, direct evidence that HLA-DRB1*04:02-restricted autoreactive CD4(+) T cells recognizing immunodominant epitopes of Dsg3 initiate the production of Dsg3-reactive IgG autoantibodies is still missing. In this study, we show in a humanized HLA-DRB1*04:02-transgenic mouse model that HLA-DRB1*04:02-restricted T cell recognition of human Dsg3 epitopes leads to the induction of pathogenic IgG Abs that induce loss of epidermal adhesion, a hallmark in the immune pathogenesis of PV. Activation of Dsg3-reactive CD4(+) T cells by distinct human Dsg3 peptides that bind to HLA-DRβ1*04:02 is tightly regulated by the HLA-DRB1*04:02 allele and leads, via CD40-CD40L-dependent T cell-B cell interaction, to the production of IgG Abs that recognize both N- and COOH-terminal epitopes of the human Dsg3 ectodomain. These findings demonstrate key cellular and humoral immune events in the autoimmune cascade of PV in a humanized HLA-transgenic mouse model. We show that CD4(+) T cells recognizing immunodominant Dsg3 epitopes in the context of the PV-associated HLA-DRB1*04:02 induce the secretion of Dsg3-specific IgG in vivo. Finally, these results identify Dsg3-reactive CD4(+) T cells as potential therapeutic targets in the future.

Tumor necrosis factor-α -308 G>A and interleukin-6 -174 G>C promoter polymorphisms and pemphigus

The objective of this study was to analyze the possible involvement of the tumor necrosis factor (TNF)-α -308 G>A and interleukin-6 (IL-6) -174 G>C polymorphisms in the susceptibility and/or disease profile of pemphigus in Egyptian patients. Detection of TNF-α -308 G>A by amplification refractory mutation system and IL-6 -174 G>C by restriction fragment length polymorphism was performed for 70 patients and 203 controls. No significant differences were observed in the distribution of TNF-α -308 in pemphigus patients and controls. However, GA+AA genotypes were more frequent in pemphigus vulgaris (PV) patients only versus controls (p(c) = 0.046). The frequency of the C allele and CC/GC genotypes of IL-6 -174 was significantly higher in pemphigus patients and those with the 2 major clinical forms (PV and pemphigus foliaceus [PF]) compared with controls (p < 0.05). Comparison of the distribution of TNF-α -308 and IL-6 -174 variants in relation to clinical type of pemphigus (PV versus PF), activity score, recurrence, and demographic data of patients revealed no significant associations. The IL-6 -174 CC genotype represents a marker of increased susceptibility to pemphigus in Egyptian patients and GG genotype can be considered a low-risk genotype; TNF-α -308 A-containing genotypes contribute to the susceptibility to PV only.

Pemphigus autoimmunity: hypotheses and realities

The goal of contemporary research in pemphigus vulgaris and pemphigus foliaceus is to achieve and maintain clinical remission without corticosteroids. Recent advances of knowledge on pemphigus autoimmunity scrutinize old dogmas, resolve controversies, and open novel perspectives for treatment. Elucidation of intimate mechanisms of keratinocyte detachment and death in pemphigus has challenged the monopathogenic explanation of disease immunopathology. Over 50 organ-specific and non-organ-specific antigens can be targeted by pemphigus autoimmunity, including desmosomal cadherins and other adhesion molecules, PERP cholinergic and other cell membrane (CM) receptors, and mitochondrial proteins. The initial insult is sustained by the autoantibodies to the cell membrane receptor antigens triggering the intracellular signaling by Src, epidermal growth factor receptor kinase, protein kinases A and C, phospholipase C, mTOR, p38 MAPK, JNK, other tyrosine kinases, and calmodulin that cause basal cell shrinkage and ripping desmosomes off the CM. Autoantibodies synergize with effectors of apoptotic and oncotic pathways, serine proteases, and inflammatory cytokines to overcome the natural resistance and activate the cell death program in keratinocytes. The process of keratinocyte shrinkage/detachment and death via apoptosis/oncosis has been termed apoptolysis to emphasize that it is triggered by the same signal effectors and mediated by the same cell death enzymes. The natural course of pemphigus has improved due to a substantial progress in developing of the steroid-sparing therapies combining the immunosuppressive and direct anti-acantholytic effects. Further elucidation of the molecular mechanisms mediating immune dysregulation and apoptolysis in pemphigus should improve our understanding of disease pathogenesis and facilitate development of steroid-free treatment of patients.

The genetics of pemphigus

Pemphigus vulgaris (PV) is an autoimmune blistering disorder with a complex etiology involving an interplay of genetic as well as environmental factors, most of which remain unknown. Despite the identification of several human leukocyte antigen (HLA) alleles as risk factors for disease, no other non-HLA genes have clearly been implicated in disease susceptibility. Newer candidate gene and whole-genome approaches are needed to illuminate the full palate of genetic risk elements in PV. Based on this information, genetic-based tools can be expected to provide a scientific rationale for future clinical decision-making by physicians and facilitate an era of personalized medicine.

Autoimmune bullous diseases the spectrum of infectious agent antibodies and review of the literature

Pemphigus and bullous pemphigoid are two autoimmune diseases that have a similar pathogenesis. Both have a genetic predisposition which promotes the production of auto-antibodies targeted against different components of the epidermal desmosome and hemidesmosome. Environmental factors play an important role in the pathogenesis of this autoimmune disease. Among these, the role of infectious agents was debated as a causative factor. We sought to determine a possible connection between various infectious agents and autoimmune bullous disease (ABD). A cohort of 148 serum samples of patients with pemphigus, bullous pemphigoid and controls was screened for evidence of a prior infection with HBV, HCV, EBV, CMV, Helicobacter pylori, Toxoplasma gondii and Treponema pallidum, utilizing the Bio-Rad BioPlex 2200 system as well as ELISA assays to complete the panel. HBV, HCV, H. pylori, T. gondii and CMV were demonstrated to have significantly higher prevalence of antibodies in patients with pemphigus and bullous pemphigoid in comparison to controls. Among them, we found a novel association between H. pylori and ABD. Our study suggests a contributing role for HBV, HCV, H. pylori, T. gondii and CMV in inducing ABD in the genetically susceptible host.

Spectrum of autoantibodies other than anti-desmoglein in pemphigus patients

BACKGROUND

Pemphigus is a life-threatening autoimmune blistering disease mediated by autoantibodies against adhesion molecule of the skin. Its concurrence with systemic and organ-specific autoimmune disease was described in case reports.

OBJECTIVES

To evaluate the presence of a broad spectrum of organ-specific and non-organ-specific autoantibodies other than anti-desmoglein antibodies in pemphigus patients.

PATIENTS AND METHODS

Serum samples were obtained from 105 pemphigus foliaceus (PF) patients, 51 pemphigus vulgaris (PV) patients and 50 controls. Both indirect immunofluorescence assay and ELISA were used to assess the presence of autoantibodies related to connective tissue diseases, autoimmune hepatitis, vasculitis, rheumatoid arthritis, coeliac disease, diabetes and thyroiditis.

RESULTS

Significant difference was observed between the three groups for anti-thyroglobulin antibodies in the pemphigus foliaceus group (18% vs. 4%, P=0.03). A significantly higher occurrence of IgM anti-cardiolipin (P=0.03), IgG anti-reticulin (P=0.01) and IgG anti-gliadin antibodies (P=0.008) were observed in the PV group. Cases with more than four autoantibodies were frequently positives for both anti-desmoglein 1 and anti-desmoglein 3.

CONCLUSION

Autoantibodies other than anti-desmoglein antibodies are not rare in pemphigus patients. Clinical and serological follow-up of pemphigus patients with positive autoantibodies are needed to clarify their impact in disease evolution.

Geoepidemiologic considerations of auto-immune pemphigus

Sporadic and endemic forms of pemphigus foliaceus exist. Incidences of the various forms of pemphigus vary from country to country: pemphigus vulgaris is most common in Europe and the USA, whereas pemphigus foliaceus is more prevalent in Northern Africa, Turkey and Southern America. Endemic pemphigus foliaceus (also known as fogo selvagem and Brazilian pemphigus foliaceus) is a variant of the disease that is frequently diagnosed in some areas of Brazil and other underdeveloped areas of the world, including Tunisia and Colombia. Both genetic and environmental factors have been associated with the occurrence of auto-immune pemphigus and endemic pemphigus is very interesting from this point of view. Most of the patients with auto-immune pemphigus are aged 40-60 years at the onset of the disease. The incidence and prevalence of pemphigus are low. The demonstration of association of pemphigus vulgaris with HLA class II alleles is supported by various studies.

Pemphigus in the XXI Century: New life to an old story

In this new century of pemphigus research, the search for novel treatments is switching from a monospecific approach, focused on immunosuppression, to a polyspecific approach that includes drugs acting on novel pathophysiologic pathways. Current research argues that acantholysis in pemphigus occurs as an active process resulting from intracellular signaling triggered as a result of IgG binding to the keratinocyte membrane antigens in a receptor-ligand fashion. Recent progress regarding the pathophysiology of pemphigus acantholysis led to, or was accompanied by, breakthrough discoveries of safer treatments. Both the identification of cell-surface receptors to acetylcholine among the nondesmoglein (Dsg) targets for pemphigus antibodies, and the elucidation of the cholinergic control of keratinocyte cell adhesion provide an explanation for the therapeutic efficacy of cholinomimetics in patients with pemphigus. In patients' skin, Fas-L, TNFalpha, and, probably, IL-1alpha act as autocrine/paracrine co-factors for anti-keratinocyte IgG. Thus, it appears that an array of interconnected signaling cascades is responsible for acantholysis and cell death in pemphigus. Future studies should define the signaling pathways mediating acantholysis that occur in individual pemphigus patients and identify the membrane proteins (receptors) triggering signaling along a specific pathway upon their ligation by autoantibodies. It will be important to determine which pathway 1) leads directly to a loss of cell-cell adhesion (primary pathway), 2) which is being activated due to cell shrinkage/detachment (secondary pathway), 3) which contributes to utilization of altered proteins and organelles (scavenging pathway), and 4) which represents the cell defense (protective pathway). To dissect out the signaling pathways originating from binding of pemphigus IgG to non-Dsg targets on the keratinocyte plasma membrane experiments should be performed in cultures of murine keratinocytes grown from the Dsg3-/- mice or human keratinocytes with the knocked-down expression of the Dsg1 and/or Dsg3 gene by the RNA interference.