Desmoglein autoimmunity in the pathogenesis of pemphigus

Autoimmune Bullous Dermatosis Following COVID-19 Vaccination: A Series of Five Cases

Autoimmune bullous diseases (AIBDs) are a heterogeneous group of diseases characterized by cutaneous and mucosal vesicles, blisters, and erosions. Several factors can trigger this disease, including vaccines; but this entity remains very rare. We hypothesized that vaccination against coronavirus disease 2019 (COVID-19) could trigger an immunological response in genetically predisposed individuals. We report five cases of new-onset autoimmune bullous diseases triggered by the COVID-19 vaccine. Clinical and histopathological examinations confirmed the diagnosis of bullous pemphigoid (BP) in three patients and pemphigus in the other two. According to the French method of imputability, the pharmacovigilance investigation showed an I5B4 causality assessment score for the vaccines, interpreted as highly probable, for all the patients. The diagnosis of vaccine-induced autoimmune bullous dermatosis was highly suspected. One patient's condition improved by dermocorticoids alone, while the other four required oral corticosteroid therapy at 0.5 mg/kg/day, which led to a favorable outcome.

Changes in N-glycans of IgG4 and its relationship with the existence of hypocomplementemia and individual organ involvement in patients with IgG4-related disease

Background

Although increased serum IgG4 level and tissue infiltration of IgG4-positive cells are key events in IgG4-related disease (IgG4RD), and nearly half of IgG4RD patients show hypocomplementemia, the role of IgG4 in the pathogenesis of IgG4RD remains unclear. Many reports show that altered IgG glycosylation, especially IgG with agalactosylated N-linked glycan (G0 N-glycan), have proinflammatory roles including complement activation, implicated in the pathogenesis of various inflammatory diseases. This study determined the concentration of N-linked glycans (N-glycan) released from serum IgG4 in IgG4RD patients and compared the difference of glycosylation changes to those in healthy controls. We also compared the concentration of each IgG4 glycoform between patients with and without hypocomplementemia and individual organ involvement (kidney, pancreas, lymph node) in IgG4RD.

Methods

We collected sera from 12 IgG4RD patients and 8 healthy controls. IgG4 was isolated from sera via Melon™ Gel IgG Spin Purification Kit followed by Capture Select IgG4 (Hu) Affinity Matrix. IgG4 N-glycans were analyzed by S-BIO GlycanMap^® Xpress methodology.

Results

Significant increases of IgG4 G0 N-glycan and IgG4 fucosylated N-glycan (F1 N-glycan) concentrations were observed in IgG4RD compared with healthy controls. Although we observed decreased levels of IgG4 F0 glycan in IgG4RD with hypocomplementemia, there were no significant differences in the galactosylation and sialyation of IgG4 N-glycans. Furthermore, there were no significant differences in the glycosylation of IgG4 N-glycans between patients with and without individual organ involvement of IgG4RD.

Conclusions

Although IgG4 has anti-inflammatory properties, IgG4 G0 and F1 glycans were increased in patients with IgG4RD. Our results suggest that decreased galactosylation of IgG4 is not related to complement activation and the differences of individual organ involvement in IgG4RD. IgG4 fucosylation change may be related to complement activation in IgG4RD. Further investigation is needed to clarify the role of IgG4 in IgG4RD.

The changing faces of IgG4-related disease: Clinical manifestations and pathogenesis

Since the earliest reports in 2001, immunoglobulin G4 (IgG4)-related disease has been defined as an autoimmune systemic disease characterized by the lymphoplasmacytic infiltration of affected tissues leading to fibrosis and obliterative phlebitis along with elevated serum IgG4 levels. Prior to this unifying hypothesis, a plethora of clinical manifestations were considered as separate entities despite the similar laboratory profile. The pathology can be observed in virtually all organs and may thus be a challenging diagnosis, especially when the adequate clinical suspicion is not present or when obtaining a tissue biopsy is not feasible. Nonetheless, the most frequently involved organs are the pancreas and exocrine glands but these may be spared. Immunosuppressants lead to a prompt clinical response in virtually all cases and prevent histological sequelae and, as a consequence, an early differential diagnosis from other conditions, particularly infections and cancer, as well as an early treatment should be pursued. We describe herein two cases in which atypical disease manifestations were observed, i.e., one with recurrent neck lymph node enlargement and proptosis, and one with jaundice. Our understanding of the pathogenesis of IgG4-related disease is largely incomplete but data support a significant role for Th2 cytokines with the contribution of innate immunity factors such as Toll-like receptors, macrophages and basophils. Further, macrophages activated by IL4 overexpress B cell activating factors and contribute to chronic inflammation and the development of fibrosis. We cannot rule out the possibility that the largely variable disease phenotypes reflect different pathogenetic mechanisms and the tissue microenvironment may then contribute to the organ involvement.

IgG4-related disease and its pathogenesis-cross-talk between innate and acquired immunity

IgG4-RD, a novel disease involving many immune-system components

IgG4-related disease (IgG4-RD) is a novel clinical entity proposed in Japan in the 21th century and is attracting strong attention over the world. The characteristic manifestations of IgG4-RD are increased serum IgG4 concentration and tumefaction by IgG4⁺ plasma cells. Although the clinical manifestations in various organs have been established, the pathogenesis of IgG4-RD is still unknown. Recently, many reports of aberrant acquired immunity such as T_h2-diminated immune responses have been published. However, many questions still remain, including questions about the pathogenesis of IgG4-RD and the roles of IgG4. In this review, we discuss the pathogenesis of IgG4-RD by focusing on the cross-talk between innate and acquired immunity.

PTPN22 1858T is not a risk factor for North American pemphigus vulgaris

Alterations in the protein tyrosine phosphatase N22 (PTPN22) gene affect the threshold for lymphocyte activation. The PTPN22 1858T polymorphism leads to uninhibited T-cell receptor cascade propagation. An elevated PTPN22 1858C/T genotype frequency has been correlated with several autoimmune disorders which have T-cell and humoral components. However, a recent Tunisian report demonstrated no association between PTPN22 1858T and patients with Pemphigus vulgaris (PV), an autoantibody-associated blistering disorder. Because PTPN22 1858T allele frequency is known to vary across ethnic populations, we conducted a case-control study investigating the relationship between PTPN22 1858T and PV in North American patients of either Ashkenazi Jewish or Caucasian (non-Ashkenazi) decent. Participant genotype was determined in 102 PV patients and 102 healthy controls by restriction fragment length polymorphism-polymerase chain reaction genotyping. Relationships were calculated using Fisher's exact tests and chi-squared tests. We report that the PTPN22 1858C/T genotype is not significantly associated with PV in either Caucasians (P = 0.83) or Ashkenazi Jews (P = 0.60). Further stratification of the patient population by gender, age of disease onset, HLA-type, family history of autoimmune disease, history of anti-desmoglein (anti-Dsg) 3 or anti-Dsg1 antibody response, history of lesion morphology, and disease duration did not uncover significant associations between the PTPN22 1858T allele and PV subgroups. Our data indicate that the PTPN22 1858T mutation is not associated with PV in the North American population. We do observe an elevation of PTPN22 1858C/T genotype frequency in male PV patients. Further investigation will be required to determine if this trend reaches significance in larger 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.

Apoptolysis: a novel mechanism of skin blistering in pemphigus vulgaris linking the apoptotic pathways to basal cell shrinkage and suprabasal acantholysis

Understanding the acantholytic pathways leading to blistering in pemphigus vulgaris (PV) is a key to development of novel treatments. A novel paradigm of keratinocyte damage in PV, termed apoptolysis, links the suprabasal acantholytic and cell death pathways to basal cell shrinkage rendering a 'tombstone' appearance to PV lesions. In contrast to apoptolysis, the classic keratinocyte apoptosis mediating toxic epidermal necrolysis causes death and subsequent sloughing of the entire epidermis. Apoptolysis includes five consecutive steps. (1) Binding of autoantibodies to PV antigens. (2) Activation of EGF receptor, Src, mTOR, p38 MAPK and other signalling elements downstream of ligated antigens, elevation of intracellular calcium and launching of the cell death cascades. (3) Basal cell shrinkage due to: (i) collapse and retraction of the tonofilaments cleaved by executioner caspases; and (ii) dissociation of interdesmosomal adhesion complexes caused by phosphorylation of adhesion molecules. (4) Massive cleavage of cellular proteins by activated cell death enzymes leading to cell collapse, and tearing off desmosomes from the cell membrane stimulating secondary autoantibody production. (5) Rounding up and death of acantholytic cells. Thus, the structural damage (acantholysis) and death (apoptosis) of keratinocytes are mediated by the same cell death enzymes. Appreciation of the unifying concept of apoptolysis have several important implications: (i) linking together a number of seemingly unrelated events surrounding acantholysis; (ii) opening new avenues of investigation into the pathomechanism of pemphigus; and (iii) creating new approaches to the treatment of pemphigus based on blocking the signalling pathways and enzymatic processes that lead to blistering.

Mediation, modulation, and consequences of membrane-cytoskeleton interactions

Elements of the cytoskeleton interact intimately and communicate bidirectionally with cellular membranes. Such interactions are critical for a host of cellular processes. Here we focus on the many types of interactions that exist between the cytoskeleton and the plasma membrane to illustrate why these cellular components can never truly be studied in isolation in vivo. We discuss how membrane-cytoskeleton interactions are mediated and modulated, and how many proteins involved in these interactions are disrupted in human disease. We then highlight key molecular and physical variables that must be considered in order to mechanistically dissect events associated with changes in plasma membrane morphology. These considerations are integrated into the context of cell migration, filopodia formation, and clathrin-mediated endocytosis to show how a holistic view of the plasma membrane-cytoskeleton interface can allow for the appropriate interpretation of experimental findings and provide novel mechanistic insight into these important cellular events.