Immunoglobulin G subclass distribution of bullous pemphigoid autoantibodies and complement fixation studies

OBJECTIVE: The purpose of this study was to examine the immunoglobulin G (IgG) subclass distribution of tissue bound and circulating antibasement membrane zone antibodies in bullous pemphigoid. In addition, the complement fixing capability of circulating IgG subclasses was also investigated.

METHODS: Seventeen skin biopsies and 25 serum samples obtained from 25 cases of bullous pemphigoid were analyzed by direct and indirect immunofluorescence using mice anti-human IgG subclasses monoclonal antibodies. Indirect complement immunofluorescence was used to measure the avidity with which antibodies activate the complement. The study was carried out between 1992 and 1996 at the King Fahd Hospital of the University, Al Khobar, Kingdom of Saudi Arabia and the Western Infirmary Immunopathology Laboratory, Glasgow, Scotland.

RESULTS: Immunoglobulin G1 deposits were detected in 10 of 17, IgG2 in one, IgG3 in 3 and IgG4 in 15 biopsies. Immunoglobulin G1 circulating antibodies were observed in 14, IgG2 in 0, IgG3 in 4 and IgG4 in 24 serum samples. Complement fixing antibodies were detected in 15 sera, 4 of which contained only IgG4 subclass.

CONCLUSION: The predominance of IgG4 subclass observed in this study is similar to previously reported results. Complement fixation capability studies revealed non-complement fixing sera and the results were not compatible with the complement binding characteristics of IgG subclasses. This suggests that other mechanisms, which do not involve the complement, may participate in blister formation in bullous pemphigoid.