Bungo Ohyama

Pemphigus autoantibodies generated through somatic mutations target the desmoglein-3 cis-interface

Pemphigus vulgaris (PV) is an autoimmune blistering disease of skin and mucous membranes caused by autoantibodies to the desmoglein (DSG) family proteins DSG3 and DSG1, leading to loss of keratinocyte cell adhesion. To learn more about pathogenic PV autoantibodies, we isolated 15 IgG antibodies specific for DSG3 from 2 PV patients. Three antibodies disrupted keratinocyte monolayers in vitro, and 2 were pathogenic in a passive transfer model in neonatal mice. The epitopes recognized by the pathogenic antibodies were mapped to the DSG3 extracellular 1 (EC1) and EC2 subdomains, regions involved in cis-adhesive interactions. Using a site-specific serological assay, we found that the cis-adhesive interface on EC1 recognized by the pathogenic antibody PVA224 is the primary target of the autoantibodies present in the serum of PV patients. The autoantibodies isolated used different heavy- and light-chain variable region genes and carried high levels of somatic mutations in complementary-determining regions, consistent with antigenic selection. Remarkably, binding to DSG3 was lost when somatic mutations were reverted to the germline sequence. These findings identify the cis-adhesive interface of DSG3 as the immunodominant region targeted by pathogenic antibodies in PV and indicate that autoreactivity relies on somatic mutations generated in the response to an antigen unrelated to DSG3.

From anti-p200 pemphigoid to anti-laminin γ1 pemphigoid

Anti‐laminin γ1 pemphigoid is an autoimmune subepidermal bullous disease first described in 1996, and has been distinct from previously known subepidermal blistering diseases, such as bullous pemphigoid and epidermolysis bullosa acquisita. Circulating autoantibodies of the patients do not react to any known autoantigen of the skin, but react to a 200‐kDa molecule (p200) from dermal extracts. The identity of p200 was unmasked as laminin γ1, an extracellular matrix glycoprotein composing several forms of laminin heterotrimers. We renamed this disease from the previously used anti‐p200 pemphigoid to anti‐laminin γ1 pemphigoid, a new entity of an autoimmune bullous disease. In this decade, we have experienced over 70 cases of this disease. Although the number of the cases of anti‐laminin γ1 pemphigoid is half as many as the number of definitely diagnosed cases of epidermolysis bullosa acquisita in the same duration, a considerable number of the cases could be clinically misdiagnosed as epidermolysis bullosa acquisita. Unveiling the pathogenicity and development of a useful diagnostic method is necessary for appropriate management of this new disease.

Epitope Spreading Is Rarely Found in Pemphigus Vulgaris by Large-Scale Longitudinal Study Using Desmoglein 2–Based Swapped Molecules

Epitope spreading is involved in inducing and maintaining self-reactivity. Epitope spreading in pemphigus vulgaris (PV), caused by IgG autoantibodies to desmoglein 3 (Dsg3) and Dsg1, was previously analyzed using Dsg3/Dsg1 extracellular domain-swapped molecules. However, precise identification of the responsible epitopes in each molecule by using only this method was problematic. In this study, we studied epitope spreading in PV by a novel immunoprecipitation-immunoblot method using Dsg3 (or Dsg1)/Dsg2 domain-swapped molecules, which overcomes the problems associated with the previous approaches. We analyzed the antigenic epitopes recognized by 212 sera collected from 53 PV patients at multiple disease stages. The major epitopes were present at the N-terminal region of Dsgs and were unchanged over the course of the disease in both anti-Dsg3 mucosal dominant-type PV and anti-Dsg3/Dsg1 mucocutaneous-type PV. These N-terminal epitopes were calcium dependent. Circulating antibodies in paraneoplastic pemphigus and pemphigus herpetiformis had unique epitope distributions, although the Dsg N-termini still contained the major epitopes. These results suggest that, after onset, intramolecular and intermolecular epitope spreading among extracellular domains on Dsg3 and Dsg1 is rare in PV and has no correlation with disease course.

Anti-desmocollin autoantibodies in nonclassical pemphigus.

Despite the established pathogenic role of anti‐desmoglein (Dsg) antibodies in classical pemphigus, the significance of autoantibodies to another desmosomal cadherin, desmocollin (Dsc) is at present unknown. No consistent immunoassay for immunoglobulin (Ig) G autoantibodies to Dscs has been developed.

IgA autoantibodies against the NC16a domain of BP180 but not 120‐kDa LAD‐1 detected in a patient with linear IgA disease

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Five Japanese cases of antidesmoglein 1 antibody‐positive and antidesmoglein 3 antibody‐negative pemphigus with oral lesions

Background  Oral mucosal lesions develop in pemphigus vulgaris, but not in pemphigus foliaceus. This clinical phenomenon is explained by the ‘desmoglein (Dsg) compensation theory’. Dsg3 and Dsg1 are major autoantigens for pemphigus vulgaris and pemphigus foliaceus, respectively. Dsg3 is overexpressed and Dsg1 is weakly expressed on the oral mucosa. Thus, on the oral mucosa, suppression of Dsg3 function by anti‐Dsg3 autoantibodies is not compensated by weakly expressed Dsg1 in pemphigus vulgaris, while suppression of Dsg1 function by anti‐Dsg1 autoantibodies is perfectly compensated by richly expressed Dsg3 in pemphigus foliaceus.

Immune response towards the amino-terminus of desmoglein 1 prevails across different activity stages in nonendemic pemphigus foliaceus.

Background  Pemphigus foliaceus (PF) is a blistering skin disease mediated by antibodies to desmoglein (Dsg) 1. The two major subtypes are nonendemic and endemic PF. A previous study in endemic PF demonstrated that changes in antibody epitope could modulate disease relapse and remission.

A case of epidermolysis bullosa acquisita with clinical features of Brunsting-Perry pemphigoid showing an excellent response to colchicine.

BACKGROUND Brunsting-Perry pemphigoid is a rare subepidermal blistering disease characterized by scarring blisters on the head and neck. However, the identity of the responsible autoantigens is still unresolved. METHODS We reported a patient with epidermolysis bullosa acquisita who had clinical features typical of Brunsting-Perry pemphigoid and investigated the involved type VII collagen epitopes. The patient was a 65-year-old Japanese woman with a 20-month history of recurrent subepidermal bullae on her head, face, and neck. RESULTS Immunoblot studies revealed that the serum of this patient reacted with type VII collagen, specifically with the noncollagenous domain 1 and the triple-helical domain. The patient responded completely to colchicine monotherapy. LIMITATIONS This study was performed on only one case. CONCLUSION This study suggests that Brunsting-Perry pemphigoid may be a clinical variant of epidermolysis bullosa acquisita.

RAC1 activation drives pathologic interactions between the epidermis and immune cells

Interactions between the epidermis and the immune system govern epidermal tissue homeostasis. These epidermis-immune interactions are altered in the inflammatory disease psoriasis; however, the pathways that underlie this aberrant immune response are not well understood. Here, we determined that Ras-related C3 botulinum toxin substrate 1 (RAC1) is a key mediator of epidermal dysfunction. RAC1 activation was consistently elevated in psoriatic epidermis and primary psoriatic human keratinocytes (PHKCs) exposed to psoriasis-related stimuli, but not in skin from patients with basal or squamous cell carcinoma. Expression of a constitutively active form of RAC1 (RACV12) in mice resulted in the development of lesions similar to those of human psoriasis that required the presence of an intact immune system. RAC1V12-expressing mice and human psoriatic skin showed similar RAC1-dependent signaling as well as transcriptional overlap of differentially expressed epidermal and immune pathways. Coculture of PHKCs with immunocytes resulted in the upregulation of RAC1-dependent proinflammatory cytokines, an effect that was reproduced by overexpressing RAC1 in normal human keratinocytes. In keratinocytes, modulating RAC1 activity altered differentiation, proliferation, and inflammatory pathways, including STAT3, NFκB, and zinc finger protein 750 (ZNF750). Finally, RAC1 inhibition in xenografts composed of human PHKCs and immunocytes abolished psoriasiform hyperplasia and inflammation in vivo. These studies implicate RAC1 as a potential therapeutic target for psoriasis and as a key orchestrator of pathologic epidermis-immune interactions.

Interaction of plectin and intermediate filaments.

BACKGROUND Plectin, a member of the plakin family proteins, is a high molecular weight protein that is ubiquitously expressed. It acts as a cytolinker for the three major components of the cyotoskeleton, namely actin microfilaments, microtubules and intermediate filaments. OBJECTIVE The aim of our experiments was to identify new binding sites for intermediate filaments on plectin and to specify these sites. METHODS We introduced truncated forms of plectin into several cell lines and observe interaction between plectin and intermediate filaments. RESULTS We found that a linker region in the COOH-terminal end of plectin was required for the association of the protein with intermediate filaments. In addition, we also demonstrated that a serine residue at position 4645 of plectin may have a role on binding of plectin to intermediate filaments. CONCLUSION A linker region in the COOH-terminal end and serine residue at position 4645 may be important for the binding of plectin to intermediate filaments.