Comparison of igg subclasses and complement binding activity of autoantibodies from patients with bullous pemphigoid and pemphigus

Abstract

Bullous pemphigoid and pemphigus are autoimmune disorders of skin of unknown etiology and are characterized by the presence of immunoreactants in the skin and circulating autoantibodies to skin components. The distribution of IgG subclass antibodies to intercellular substance (ICS) of pemphigus and basement membrane zone substance (BMZ) of bullous pemphigoid was analyzed by using monoclonal antibodies to human IgG subclasses. IgG, type anti‐BMZ antibody was found in the majority of patients with bullous pemphigoid (88% in skin and 96% in serum). One third to one half of bullous pemphigoid patients had lgG, and IgG, anti‐BMZ antibodies. The majority of bullous pemphigoid skin (92%) had complement in skin, however only one third of their sera had complement binding activity in vitro. lgG, anti‐ICS antibody was the predominant one in patients with pemphigus (86% in skin and 80% in circulation). IgG4 anti‐ICS antibody was seen in two thirds of specimens from pemphigus patients. IgG, subclass antibody was more frequently seen in pemphigus than in bullous pemphigoid patients. Two‐thirds of pemphigus sera were capable of activating complement in vitro. The complement binding activity was directly associated with IgG₁ and/or IgG₃ subclass antibodies. The possible mechanisms for the restricted IgG₄ subclass antibodies in bullous pemphigoid and pemphigus are discussed.