Significance of IgG-subclass antibody determinations in bullous pemphigoid

The presence of circulating basement membrane zone (BMZ) antibodies is characteristic of patients with bullous pemphigoid (BP) and are routinely employed in making the diagnosis. The positive tests, however, occur in 50-70% of patients with BP, thus necessitating consideration of other tests in a significant number of patients. The purpose of this study was to examine the efficacy of indirect immunofluorescence (IF) tests specific for various IgG subclasses antibodies to BMZ in BP, especially in patients who are seronegative on routine indirect IF tests with fluorescein-conjugated antibodies to IgG. BMZ antibodies primarily are of IgG4 subclass and are present in all BMZ antibody positive BP cases. Of BP patients negative for BMZ antibodies, 72% were found positive when tested for IgG4 subclass antibodies. In conclusion, testing for IgG4 subclass BMZ antibodies enhances the sensitivity of serum tests from 68.5% to 91%. This may be due in part to the inherent increased sensitivity of the assay and for detecting subclasses of IgG and in part, due to the subclass distribution of the BP antibodies.