The Plant Lectin Wheat Germ Agglutinin Inhibits the Binding of Pemphigus Foliaceus Autoantibodies to Desmoglein 1 in a Majority of Patients and Prevents Pathomechanisms of Pemphigus Foliaceus In Vitro and In Vivo

Wheat germ agglutinin as a counterstain for immunofluorescence studies of equine hoof lamellae

Equine laminitis is a common, painful, debilitating condition of the hoof that is a leading cause of disability in horses, often necessitating euthanasia. The equine hoof represents an extreme evolutionary adaptation of an epidermal structure homologous to the human or murine nail units. Immunohistochemistry is frequently utilized in the study of the pathophysiology of laminitis. The complex, multilayered, extensively interdigitated epidermal-dermal lamellar interface renders precise interpretation of immunofluorescence localization difficult, especially when effective technique and reagents render non-reactive tissues completely dark. Fluorescent-conjugated wheat germ agglutinin (WGA) selectively labels dermal extracellular matrix fibres and epidermal cell membranes in tissue sections of horse hoof lamellae, is compatible with indirect immunofluorescence and augments interpretation of indirect immunofluorescence antigen localization. The current report details the use of WGA as a rapid, simple, economical counterstain for immunofluorescence studies of the equine hoof and may have application to other complex epidermal tissue structures.

The Thomsen-Friedenreich antigen-binding lectin jacalin interacts with desmoglein-1 and abrogates the pathogenicity of pemphigus foliaceus autoantibodies in vivo

Pemphigus foliaceus (PF) is an autoimmune skin blistering disease mediated by pathogenic autoantibodies against the desmosomal core glycoprotein desmoglein-1 (Dsg1). This study demonstrated that the O-glycan-specific plant lectin jacalin binds Dsg1 and inhibits the interaction of Dsg1/PF IgG. N-glycosylation is not involved in the interaction of Dsg1/jacalin or Dsg1/PF IgG. Subcutaneous injection of jacalin into neonatal mice drastically reduced PF IgG deposition at the epidermal cell surface and blocked PF IgG-induced skin blisters, both clinically and histologically. Interestingly, another plant lectin, peanut agglutinin, which shares the same carbohydrate specificity toward the O-linked carbohydrate structure known as Thomsen-Friedenreich antigen (TF antigen, Galβ1-3GalNAcα-O-Ser/Thr), also bound Dsg1 and blocked the skin blistering. In contrast, the plant lectin vicia villosa-B4 (VVL-B4), which shares the carbohydrate specificity toward the O-linked monosaccharide known as Thomsen-nouveau antigen (GalNAc-α1-O-Ser/Thr), did not bind Dsg1 and did not show a protective effect against the disease induced by the autoantibodies. Collectively, these results suggest that the binding of jacalin to O-linked TF carbohydrate motifs on Dsg1 impairs the Dsg1/PF autoantibody interactions and abrogates its pathogenicity in vivo. TF-specific binding ligands may have a potential therapeutic value for PF.

Experimental human cell and tissue models of pemphigus

Pemphigus is a chronic mucocutaneous autoimmune bullous disease that is characterized by loss of cell-cell contact in skin and/or mucous membranes. Past research has successfully identified desmosomes as immunological targets and has demonstrated that acantholysis is initiated through direct binding of IgG. The exact mechanisms of acantholysis, however, are still missing. Experimental model systems have contributed considerably to today's knowledge and are still a favourite tool of research. In this paper we will describe to what extent human cell and tissue models represent the in vivo situation, for example, organ cultures of human skin, keratinocyte cultures, and human skin grafted on mice and, furthermore, how suitable they are to study the pathogenesis of pemphigus. Organ cultures closely mimic the architecture of the epidermis but are less suitable to answer posed biochemical questions. Cultured keratinocyte monolayers are convenient in this respect, but their desmosomal make-up in terms of adhesion molecules does not exactly reflect the in vivo situation. Reconstituted skin is a relatively new model that approaches organ culture. In models of human skin grafted on mice, acantholysis can be studied in actual human skin but now with all the advantages of an animal model.

High Throughput Quantitative Glycomics and Glycoform-focused Proteomics of Murine Dermis and Epidermis

Despite recent advances in our understanding of the significance of the protein glycosylation, the throughput of protein glycosylation analysis is still too low to be applied to the exhaustive glycoproteomic analysis. Aiming to elucidate the N-glycosylation of murine epidermis and dermis glycoproteins, here we used a novel approach for focused proteomics. A gross N-glycan profiling (glycomics) of epidermis and dermis was first elucidated both qualitatively and quantitatively upon N-glycan derivatization with novel, stable isotope-coded derivatization reagents followed by MALDI-TOF(/TOF) analysis. This analysis revealed distinct features of the N-glycosylation profile of epidermis and dermis for the first time. A high abundance of high mannose type oligosaccharides was found to be characteristic of murine epidermis glycoproteins. Based on this observation, we performed high mannose type glycoform-focused proteomics by direct tryptic digestion of protein mixtures and affinity enrichment. We identified 15 glycoproteins with 19 N-glycosylation sites that carry high mannose type glycans by off-line LC-MALDI-TOF/TOF mass spectrometry. Moreover the relative quantity of microheterogeneity of different glycoforms present at each N-glycan binding site was determined. Glycoproteins identified were often contained in lysosomes (e.g. cathepsin L and gamma-glutamyl hydrolase), lamellar granules (e.g. glucosylceramidase and cathepsin D), and desmosomes (e.g. desmocollin 1, desmocollin 3, and desmoglein). Lamellar granules are organelles found in the terminally differentiating cells of keratinizing epithelia, and desmosomes are intercellular junctions in vertebrate epithelial cells, thus indicating that N-glycosylation of tissue-specific glycoproteins may contribute to increase the relative proportion of high mannose glycans. The striking roles of lysosomal enzymes in epidermis during lipid remodeling and desquamation may also reflect the observed high abundance of high mannose glycans.

Desmoglein-1 is a minor autoantigen in dogs with pemphigus foliaceus

The majority of human patients with pemphigus foliaceus (PF) have circulating IgG autoantibodies that target conformational epitopes on the desmosomal cadherin desmoglein-1 (dsg1). Limited studies using immunoblot techniques suggested that the principal autoantigen in dogs with PF might also be dsg1. It was the objective of this study to test this hypothesis. A comprehensive survey of canine PF sera was conducted using a novel screening strategy that detects conformational epitopes. This method consists of the ectopic expression of canine dsg1 at the surface of human 293T epithelial kidney cells and their live screening, i.e. prior to fixation. Out of seven control human PF sera that bound to canine epidermis, three (57%) contained IgG autoantibodies that recognized ectopically expressed canine dsg1 with a membrane and punctate pattern. Out of 83 canine PF sera only five (6%) contained IgG that recognized canine dsg1. Consistent with findings for human PF sera obtained in this study, autoantibody binding was conformation- and glycosylation-dependent as demonstrated by calcium chelation with EDTA and tunicamycin or wheat germ agglutinin treatment, respectively. In conclusion, these studies establish canine dsg1 as a minor autoantigen for canine PF. Antigenic epitopes appear to be conformation- and glycosylation-dependent.

Avancées moléculaires dans la physiopathologie des maladies bulleuses autoimmunes

Autoimmune blistering skin diseases are characterized by the production of autoantibodies directed against adhesive structures of the skin. These organ specific autoimmune diseases included pemphigus in which autoantibodies target proteins of the desmosomal complex, and subepidermal autoimmune diseases characterized by autoantibodies directed against structural proteins of the dermoepidermal junction. Binding of autoantibodies to their targets induces a loss of adhesion between keratinocytes in pemphigus and alterations of the dermoepidermal junction in subepidermal autoimmune diseases. Progresses during the last twenty years had allowed the identification of target autoantigens and the characterization of their adhesive functions, a better understanding of the pathogenesis of these diseases and the development of new diagnostic tools.

Techniques: species' finest blend--humanized mouse models in inflammatory skin disease research

Differences between humans and mice often hamper the transfer of promising results from the bench to the clinic. For ethical reasons, research that involves patients is limited, and so there is an urgent need for models that mimic the human situation as closely as possible. In recent years, there has been considerable progress in generating humanized mouse models, and their application to drug discovery has proved fruitful. So, how can mice be humanized, and how can humanized mice be employed in immunology research and drug discovery? In this article, we answer these questions, focusing on T-cell-mediated skin diseases as an example.