Immunohistochemistry for Immunoglobulin G4 on Paraffin Sections as a Diagnostic Test for Pemphigus

Pemphigus is a group of autoimmune bullous diseases mediated by autoantibodies most often of the immunoglobulin G class, subclasses immunoglobulin G1, and immunoglobulin G4 (IgG4), directed against desmosomal adhesion proteins of keratinocytes. This study aimed to evaluate IgG4 immunoreactivity on paraffin sections using immunohistochemistry in patients with pemphigus as a diagnostic test. Fifty formalin-fixed paraffin-embedded specimens from patients with pemphigus were selected. Fifty formalin-fixed paraffin-embedded specimens from patients with bullous diseases other than pemphigus were used as controls. Biopsies were performed on active lesions in newly diagnosed patients. Immunohistochemistry for IgG4 was performed on paraffin sections with an anti-immunoglobulin G4 antibody. Positivity was defined as distinctive, uninterrupted immunoreactivity localized to the intercellular junctions of keratinocytes. A finding that did not meet these criteria was defined as negative. Forty-three (86.0%) of the examined patients had pemphigus vulgaris and 7 (14%) had pemphigus foliaceus. Forty-nine (98.0%) specimens from patients with pemphigus were immunoreactive for IgG4, 1 (2%) upper back biopsy from the patient with oral pemphigus showed negative immunoreactivity for IgG4. Negative immunoreactivity was found in 45 (90%) controls. Five (10%) controls with bullous pemphigoid showed immunoreactivity for IgG4. Sensitivity of the method was established to be 98% and specificity 90%. Immunohistochemical examination for IgG4 for the diagnosis of pemphigus can be applied when direct immunofluorescence examination is unavailable. The advantage of this method is that it does not require special equipment and the histology slides are permanent.