Noncomplement fixing, IgG₄ autoantibodies predominate in patients with anti-epiligrin cicatricial pemphigoid

This study characterized the specific reactivity, IgG subclass, and complement fixing ability of anti-laminin-5 IgG from 12 patients with anti- epiligrin cicatricial pemphigoid. Circulating IgG from all patients bound the dermal side of 1 M NaCl split skin, immunoprecipitated laminin-5 produced by biosynthetically radiolabeled human keratinocytes, and (in 10 of 12 cases) immunoblotted the laminin-α3 subunit. Analysis of the distribution of IgG subclasses in these patients' circulating anti-laminin-5 autoantibodies by semiquantitative indirect immunofluorescence microscopy using the HP series of subclass-specific monoclonal antibodies revealed: (i) IgG₄ predominant autoantibodies in seven of 11 sera; (ii) IgG₁ and IgG₂ at substantially lower levels in a smaller number of sera; and (iii) no specific IgG₃ anti- laminin-5 autoantibodies in any patients. The same IgG₄-dominant profile of anti-laminin-5 autoantibodies was found in enzyme-linked immunosorbent assay studies of purified human laminin 5. Direct immunofluorescence microscopy of six skin biopsies from three patients found that IgG₄ was also the predominant subclass of IgG in epidermal basement membranes in situ. Consistent with these findings, sera from 11 of 11 patients with anti- laminin-5 IgG autoantibodies did not fix C3 to epidermal basement membranes in vitro. These immunochemical studies suggest that complement activation does not play a major role in the pathophysiology of this disease and that subepidermal blisters in these patients may develop via a direct effect of anti-laminin-5 IgG itself.