NONCOMPLEMENT FIXING, IGG(4) AUTOANTIBODIES PREDOMINATE IN PATIENTS WITH ANTI-EPILIGRIN CICATRICIAL PEMPHIGOID

This study characterized the specific reactivity, IgG subclass, and co mplement fixing ability of anti-laminin-5 IgG from 12 patients with an ti-epiligrin cicatricial pemphigoid. Circulating IgG from all patients bound the dermal side of 1 M NaCl split skin, immunoprecipitated lami nin-5 produced by biosynthetically radiolabeled human keratinocytes, a nd (in 10 of 12 cases) immunoblotted the laminin-alpha 3 subunit. Anal ysis of the distribution of IgG subclasses in these patients' circulat ing anti-laminin-5 autoantibodies by semiquantitative indirect immunof luorescence microscopy using the HP series of subclass-specific monocl onal antibodies revealed: (i) IgG(4) predominant autoantibodies in sev en 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 a nti-laminin-5 autoantibodies was found in enzyme-linked immunosorbent assay studies of purified human laminin 5. Direct immunofluorescence m icroscopy of six skin biopsies from three patients found that IgG(4) w as also the predominant subclass of IgG in epidermal basement membrane s in situ. Consistent with these findings, sera from 11 of 11 patients with anti-laminin-5 IgG autoantibodies did not fur C3 to epidermal ba sement membranes in vitro. These immunochemical studies suggest that c omplement 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.