Subclass characteristics of IgG autoantibodies in bullous pemphigoid and pemphigus

Immunoglobulin (Ig) G subclasses in anti-basement membrane zone (BMZ) autoantibodies found in the sera of bullous pemphigoid (BP) and in anti-intercellular substance (ICS) autoantibodies of pemphigus were investigated using immunofluorescent (IF) staining. In BP, IgG4, IgG1, and IgG2 were detected in 13, 5 and 6 of 15 patients, respectively; IgG3 was not detected. In pemphigus, IgG4 was detected in all of 10 patients, IgG1 in 7, IgG2 in one, and IgG3 in one patient, respectively. In both BP and pemphigus, the most prominent subclass in intensity of IF staining was IgG4. Although one BP and one PV patient had only IgG4 autoantibodies, C3 deposition was detected. The quantification of IgG subclasses in the sera of the patients was performed by enzyme-linked immunosorbent assays (ELISA). Serum levels of IgG4 in both BP and pemphigus were elevated approximately 3-fold over those in normal controls; those of whole IgG and IgG1-3 were not significantly elevated. Using direct IF staining, the deposition of C3 at the BMZ and at the ICS was demonstrated in 9 of 10 BP and in 3 of 8 pemphigus patients, respectively. The prominent IgG subclasses of anti-BMZ and anti-ICS antibody were IgG4, a noncomplement-fixing antibody, suggesting that the deposition of C3 in the lesional skin occurred via the alternative pathway, or that small amounts of IgG1-3 subclass autoantibodies activated the classical pathway.