Noncomplement fixing, IgG(4) 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-alpha 3 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) IgG(4) predominant autoantibodies in seven of 11 sera; (ii) IgG(1) and IgG(2) at substantially lower levels in a smaller number of sera; and (iii) no specific IgG(3) anti-laminin-5 autoantibodies in any patients. The same IgG(4)-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 IgG(4) 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 fur 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.