AUTOANTIBODIES FROM PATIENTS WITH CICATRICIAL PEMPHIGOID TARGET DIFFERENT SITES IN EPIDERMAL BASEMENT-MEMBRANE

Indirect immunogold electron microscopy studies of cryofixed, freeze-s ubstituted, and post-embedded normal human skin were performed to loca lize precisely the ultrastructural binding site of circulating autoant ibodies from two groups of patients with cicatricial pemphigoid, One g roup of patients had circulating IgG autoantibodies that bound the der mal side of 1 M NaCl-split skin and immunoprecipitated epiligrin. The other group of patients had circulating IgG autoantibodies directed ag ainst the epidermal side of 1 M NaCl-split skin and showed no specific reactivity to any keratinocyte polypeptide by immunoprecipitation. Ig G autoantibodies from all patients with anti-epiligrin cicatricial pem phigoid bound the lowermost aspect of the lamina lucida at its interfa ce with the lamina densa; the greatest staining was seen beneath and b eside hemidesmosomes. In contrast, IgG from cicatricial pemphigoid pat ients whose autoantibodies bound the epidermal side of M NaCl-split sk in localized to hemidesmosomes and the junction between hemidesmosomes and the plasma membranes of basal keratinocytes. Although the latter staining pattern is similar to that observed with anti-BPAG2 autoantib odies, sera from our patients with cicatricial pemphigoid did not bind BPAG2 in immunoprecipitation studies of radiolabeled human keratinocy te extracts or show immunoblot reactivity to a fusion protein correspo nding to the immunodominant epitope of this polypeptide. These studies demonstrate the following: 1) Autoantibodies from patients with anti- epiligrin cicatricial pemphigoid consistently bind the lower lamina lu cida at its interface with the lamina densa; and 2) other patients wit h the same phenotype may have IgG autoantibodies against yet-unknown e pitopes in basal keratinocytes.