Lichen planus pemphigoides with IgG autoantibodies to the 180 kd bullous pemphigoid antigen (type XVII collagen) (1)
Lichen planus pemphigoides (LPP) is characterized by a concomitant presence of subepidermal bullae and lichen planus-like lesions. A typical case of LPP with IgG autoantibodies directed against the 180 kd BP antigen (BPAg2, type XVII collagen). These findings provide evidence for similarity of immunopathology between LPP and bullous pemphigoid (BP).
Histologic examination of one of the papules revealed a lichenoid lymphohistiocytic infiltrate at the dermoepidermal junction, dyskeratotic keratinocytes, wedge-shaped hypergranulosis, and orthokeratosis, consistent with LP. Physical examination revealed numerous tense bullae either on an urticarial base or on normal-appear- ing skin, among lesions characteristic of LP.
Histologic examination of one of the bullous lesions revealed a subepidermal blister with numerous eosinophils.
Dermoepidermal separation
Strips (3 x 2 cm) of normal human skin were obtained from patients undergoing mammoplasty, and washed in phosphate-buffered saline (PBS) (0.126 mol/L NaCl, 0.008 mol/L Na2HPO4, and 0.002 mol/L KH2PO4, pH 7.2). Dermoepidermal separation was performed by incubating the skin pieces with a 1 mol/L NaCl solution containing 10 mmol/L phenylmethylsulfonylfluoride (PMSF) at 4°C for 72 hours.
Protein lysate
After dermoepidermal separation by either 1mol/L NaCl or 20 mmol/L EDTA, the epidermis was physically peeled from the dermis, and the dermal proteins were extracted with 8 moliL urea and 0.3 mol/L P-mercaptoethanol in 25 mmol/L TRIS buffer (pH 7.8) with 10 mmol/L PMSF by incubating for 45 minutes in an agitator at 4°C. The tissue remnants were removed by centrifugation at 13,000g for 25 minutes at 4°C. The supernatants were stored at -20°C until used.
Indirect immunofluorescence microscopy displayed IgG anti-BMZ antibodies in the patient’s serum that selectively reacted with the epidermal side of SSS, suggesting that they are directed against an epidermal component of the basement membrane. This pattern was quite similar to that found by a rabbit polyclonal antibody raised against the BPAg2 (R67).
The patient’s serum reacted with the epidermal protein extract and labeled exclusively a 180 kd antigen comigrating with the BPAg2 identified by a polyclonal anti-BPAg2 (R67). The patient’s serum did not react with the 290 kd dermal antigen (type VII collagen) or the laminin-5 subunits (alpha 3, beta 3, gamma 2). Immunoaffinity-purified anti-180 kd IgG antibodies further labeled the skin BMZ, and bound to the epidermal side of SSS.
The classification of LPP has been controversial. It is merely a coexistence of LP and BP; others have suggested that LPPis a separate, unique bullous disease. There have been fewer than a dozen reports on the identification of the antigen or antigens in LPP by immunoblot analyses. Most of these reports have identified the 230 kd or the 180 kd BP antigens. However, Davis et al reported the identification of a 200 kd protein in 2 patients and suggested that the target antigen in LPP may be different from that in BP The 190-200 kd antigen is, however, recognized by some sera from patients with BP or from normal individuals.