IgG subclasses of intercellular antibodies in Brazilian pemphigus foliaceus--the relationship to complement fixing capability.

Human IgG possesses four main subclasses, namely IgG1, IgG2, IgG3, and IgG4, of these IgG1-IgG3 fix complement, but IgG4 does not. We have studied the IgG subclasses of intercellular antibodies in the sera from 20 patients with Brazilian pemphigus foliaceus by immunofluorescent staining using mouse monoclonal antibodies against human IgG1-IgG4. At the same time, the complement fixing capability of each antibody was examined by complement immunofluorescence. All of four subclasses were frequently detected in most cases with varying distributions. However, no specific pattern was observed. Complement fixing antibodies were found in four patients. However, the distribution of IgG subclasses was incompatible with their known characteristics in terms of complement activation. This discrepancy increases the controversy over the importance of the complement system in blister formation in pemphigus.