Autoantibodies present in the sera of patients with bullous pemphigoid (BP) bind to the basement membrane zone of normal human skin and commonly recognize two epidermal proteins, the BP240 and BP180 antigens. Two BP antigen cDNA clones from a lambda gtl1 human keratinocyte library have been identified on the basis of reactivity with a BP serum. The fusion protein (FP) produced by one clone immunoadsorbed autoantibodies, which specifically recognized the BP180 antigen, showing no cross-reactivity with BP240 by immunoblot analysis. The FP produced by the second clone immunoadsorbed autoantibodies which specifically reacted with the BP240 epidermal antigen. Northern blot analysis demonstrated that the BP180 and BP240 antigens are encoded by distinct RNA transcripts with lengths of 6.0 and 8.5 kb, respectively. Immunoblot analysis of the BP180 lysogen extract identified a 135-kD FP which was recognized by 7 of 16 BP sera and 7 of 8 herpes gestationis sera. A rabbit antiserum prepared against the lysogenic BP180 FP specifically recognized the BP180 antigen from human epidermal extracts by immunoblotting, labeled the BMZ by indirect immunofluorescence, and bound to human epidermal hemidesmosomes by immuno-electron microscopy. These results indicate that the BP180 antigen recognized by BP and herpes gestationis autoantibodies is a unique hemidesmosomal polypeptide, distinguishable from the BP240 antigen. (J. Clin. Invest. 1990.

Bullous pemphigoid (BP) is an autoimmune disease characterized by subepidermal vesicles and the presence of autoantibodies directed against the epidermal basement membrane zone. Previous studies have identified two protein components of the hemidesmosome, BP180 and BP230, as the primary antigenic targets of BP autoantibodies. We have recently reported the isolation of a 1.0-kb BP180 cDNA. Sequence analysis presented in this report reveals that this partial BP180 cDNA encodes two protein domains which have primary structures that are characteristic of the triple helical domains of collagens, i.e., glycine appears at every third position and over one-third of the remaining residues are proline. The two collagen domains have lengths of 242 and 30 amino acids and are separated by a noncollagen stretch of 12 amino acids. Collagenase digestion of the BP180 cDNA-encoded fusion protein generated a peptide fragment with a size that was consistent with the predicted locations of the collagenase digestion sites. A possible physiological function for the collagen domains of the BP180 hemidesmosomal protein may be to form stable interactions with constituents of the extracellular matrix of the cutaneous basement membrane zone. Such interactions may provide the molecular framework for the adhesion between the basal keratinocyte and the basal lamina. (J. Clin. Invest. 1991.87:734-738.)

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