Demonstration of the Complement Regulating Protein, β1H, in Skin Biopsies from Patients with Bullous Pemphigoid

β1H-globulin is a recently characterized plasma protein which regulates the biologic activities of the major fragment of the third complement component, C3b. The major function of this protein is to act as a co-factor for C3b Inactivator (C3bINA) in the cleavage of C3b to an intermediate molecule, C3b', consisting of an intact β-chain covalently bound by disulfide bridges to 2 α-chain fragments of 40,000 and 67,000 daltons. Final cleavage of C3b' to the C3c and C3d fragments requires an additional protease such as plasmin or elastase. Additionally, β1H interferes with the activity of the alternative pathway convertases, C3bBb¯ and C3bBbP¯, by displacing or competing with the binding of factor B. In this study, perilesional skin biopsies from 10 patients with active bullous pemphigoid were examined for the presence of β1H at the dermal-epidermal junction by immunofluorescent methods. The protein was found in 8 of 9 biopsies in which C3 also was deposited. In a single case where C3 was not found, β1H was not seen. These findings suggest that β1H plays a role in the in vivo control of C3b and provides additional evidence for the participation of the complement system in the pathogenesis of bullous pemphigoid.