Background: Pemphigus vulgaris (PV) and pemphigus foliaceus (PF) are potentially fatal blistering diseases caused by autoantibodies targeting desmoglein adhesion proteins. Previous studies have shown an IgG4>IgG1 predominance of anti-desmoglein antibodies in pemphigus; however, no studies have examined total serum IgG4 levels in pemphigus. IgG4 is induced by chronic antigen stimulation, which could occur with persistent skin blistering and potentially elevate the total serum IgG4 relative to other IgG subclasses in pemphigus patients.
Objectives: The primary aim of the study was to quantitate total and desmoglein-specific IgG subclasses in pemphigus patients.
Methods: IgG subclasses and desmoglein-specific IgG1 and IgG4 were quantitated in PV, PF, and age-matched normal sera using a subclass ELISA. The effectiveness of IgG4 depletion in blocking PV IgG pathogenicity was determined using a keratinocyte dissociation assay.
Results: Desmoglein-specific antibodies comprised a median of 7.1% and 4.2% of total IgG4 in PV and PF patients, with 8-fold and 4-fold enrichment in IgG4 versus IgG1. Total serum IgG4, but not other IgG subclasses, was enriched in PV and PF patients compared to age-matched controls (p=0.004 and p=0.005, respectively). IgG4 depletion of PV sera reduced pathogenicity in a keratinocyte dissociation assay and showed that affinity-purified IgG4 is more pathogenic than other serum IgG fractions.
Conclusions: Desmoglein-specific autoantibodies are significantly enriched in IgG4, which may explain the enrichment of total serum IgG4 in some pemphigus patients. By preferentially targeting autoimmune rather than beneficial immune antibodies, IgG4-targeted therapies may offer safer treatment options for pemphigus.