Purification of bullous pemphigoid IgG subclasses and their capability for complement fixation.

The antibody reactivity and complement fixing capability of circulating IgG subclass antibodies of patients with bullous pemphigoid (BP) were investigated. Four subclasses of polyclonal IgG were purified from the sera of BP patients. The first stage of purification was a combination of chromatographies on DEAE Affi-Gel Blue and protein A-Cellulofine columns. The four polyclonal IgG subclasses were then isolated from the above-mentioned semi-purified subclass fractions using IgG subclass-specific immuno-affinity chromatographies. Using an immunohistopathological technique, IgG deposits were detected at the basement membrane zone (BMZ) in the normal skin incubated with IgG subclasses other than IgG3. C3 deposits were detected at BMZ in the skin incubated with IgG1. Neither IgG nor C3 deposits were in skin incubated with IgG3. These findings suggest that the subclasses of circulating BP antibodies are IgG1, IgG2 and IgG4, but not IgG3. Moreover, only the BP IgG1 subclass appears to fix complement.