Cicatricial pemphigoid differs from bullous pemphigoid and pemphigoid gestationis regarding the fine specificity of autoantibodies to the BP180 NC16A domain

Bullous pemphigoid (BP), pemphigoid (herpes) gestationis (PG), cicatricial pemphigoid (CP), and lichen planus pemphigoides (LPP) are autoimmune subepidermal bullous diseases that are characterized by circulating autoantibodies to the transmembrane hemidesmosomal protein BP180/type XVII collagen. Previous studies demonstrated that the majority of patients with BP, PG, and LPP show antibodies to an immunodominant, membrane-proximal non-collagenous domain (NC16A) on the extracellular portion of BP180. By the use of non-overlapping peptides of the NC16A domain, we previously demonstrated that autoantibodies from BP and PG patients mainly react with epitopes clustered within the N-terminus of this immunodominant site of BP180; antibodies from patients with LPP also recognized the C-terminal portion of NC16A. However, some of these results had been obtained indirectly by preadsorption studies. The aim of the present study was to analyze the fine specificity of IgG autoantibodies to NC16A in sera from patients with CP and to compare their reactivity with antibodies from BP, PG, and LPP patients using a series of new overlapping fragments covering the entire NC16A domain. We confirm that BP and PG sera mainly react with N-terminal epitopes of NC16A, whereas sera from patients with LPP also bind to C-terminal portions of this domain. Interestingly, out of ten patients with CP, the sera of seven reacted with NC16A; within NC16A, these sera bound to both C-terminal fragments and an N-terminal epitope right next to the cell membrane. Our data demonstrate a heterogeneous binding pattern of autoantibodies to BP180 NC16A in patients with CP.