DIFFERENCE IN BINDING-SITES OF AUTOANTIBODIES AGAINST 230-KD AND 170-KD BULLOUS PEMPHIGOID ANTIGENS ON SALT-SPLIT SKIN

The purpose of this study is to clarify a relationship between bullous pemphigoid autoantibodies against two major BP antigens, 230 kilodalt on (kD) (BPAG1) and 180 kD (BPAG2) and their binding sites, using immu noblot analysis and indirect immunofluorescence on salt-split skin. Of the 135 sera obtained from patients in whom bullous pemphigold had pr eviously been diagnosed by clinical and immune pathologic criteria, al l 52 sera recognizing only BPAG1 stained only the epidermal side of sp lit skin (epidermal pattern). Of 24 sera recognizing only BPAG2, 20 sh owed the epidermal pattern and four stained both the epidermal and der mal sides (combined pattern). Of 42 recognizing both BPAG1 and BPAG2, 35 showed the epidermal pattern and seven showed the combined pattern. Of 17 that reacted with neither antigen, nine showed the epidermal pa ttern, four showed the combined pattern, and four stained only the der -mal side (dermal pattern). Two of the four cases that showed a dermal pattern were retrospectively identified as epidermolysis bullosa acqu isita. Immunoelectron microscopy confirmed that a serum with combined pattern bound to both intracellular and extracellular sites of hemides mosomes. Our results suggest that autoantibodies that react solely wit h BPAG1 bind exclusively to the epidermal side of salt-split skin and never show either a combined or a dermal pattern, and that most antibo dies against BPAG2 bind to the epidermal side. The combined pattern su ggests the presence of autoantibodies against the extracellular epitop es of BPAG2 that are separated from the epidermis during the salt-spli tting process.