Lichen planus pemphigoides with IgG autoantibodies to the 180 kd bullous pemphigoid antigen (type XVII collagen).

We describe a 75-year-old patient with pruritic papules on her trunk and extremities, typical of lichen planus, who later experienced subepidermal blisters. These clinical features are consistent with lichen planus pemphigoides. Immunofluorescence of perilesional skin showed linear deposits of C3 along the dermoepidermal junction. Circulating IgG autoantibodies were found to be directed against an epidermal component of the dermoepidermal junction because the patient's serum labeled the epidermal side of 1 mol/L NaCl-split skin. The patient's IgG autoantibodies were directed exclusively against the 180 kd bullous pemphigoid antigen (BPAg2, type XVII collagen) detected in human keratinocyte lysate by Western blot assay. No reactivity was found against the 230 kd bullous pemphigoid antigen, type VII collagen, or the laminin-5 subunits. This study demonstrates that BPAg2 is recognized, not only by bullous pemphigoid sera, but also by lichen planus pemphigoides sera. Our findings attest to the similarity of immunopathology in these two subepidermal blistering skin diseases.