Simultaneous immunolocalization of desmoglein 3 and IgG4 in oral pemphigus vulgaris: IgG4 predominant autoantibodies in its pathogenesis.

Oral pemphigus vulgaris (PV), an autoimmune blistering disease, is mainly mediated by autoantibodies against desmoglein (Dsg) 3. However, no attention has been paid to IgG subclasses of the autoantibodies against Dsg3 in the diagnostic procedure for PV. Thus, our aim in this study was to investigate whether Dsg3 and any of IgG subclasses are immunohistochemically colocalized in tissue sections of PV oral mucosa. Serial sections cut from formalin-fixed paraffin blocks of biopsy specimens of 9 PV cases and those of normal buccal mucosa surgically removed for fibro-epithelial polyps were comparatively examined for immunohistochemical localizations for Dsg3, IgG4, and IgG. Dsg3 was demonstrated in a dot-like pattern on the cell border and in the cytoplasm of the whole epithelial layer in both normal and PV specimens, while its staining was irregular among floating epithelial sheets of PV. IgG4 was also demonstrated in a punctuated fashion on the cell border among floating epithelial sheets, which was nearly identical to the immunohistochemical profile of Dsg3. In addition to being detected in the epithelial part, IgG4 signals were prominently localized in plasma cells scattered in the granulation tissue, where ratios of IgG4-positive (+) plasma cells to IgG+ cells were extraordinarily higher (mean 28%) than those in normal mucosa. These findings confirmed for the first time that autoantibodies against Dsg3 are mainly composed of IgG4 in oral PV and that the combined immunohistochemistry for Dsg3 and IgG4 can be a valuable aid in confirming a histopathological diagnosis of PV.