IgG autoantibodies in patients with anti-epiligrin cicatricial pemphigoid recognize the G domain of the laminin 5 α-subunit

Anti-epiligrin cicatricial pemphigoid (AECP) is a mucosal-predominant, subepithelial blistering disease characterized by IgG anti-basement membrane autoantibodies to laminin 5 (α3β3γ2). This and prior studies found that autoantibodies from most patients recognize the α-subunit of this laminin isoform. Accordingly, sera from 10 representative patients were tested against prokaryotic recombinants of this polypeptide in epitope mapping studies. cDNAs spanning the full length of the α-subunit were generated by PCR, directionally cloned into the pGEX-4T-3 vector, and expressed as glutathione-S-transferase fusion proteins of appropriate size and immunoreactivity. Sera from 9 of 10 AECP patients immunoblotted fusion proteins corresponding to subdomains G2, G3, G4, and G5 at the carboxyl terminus of the laminin 5 α-subunit. Serum from 1 patient (and that from normal volunteers) showed no reactivity to any fusion proteins; no sera bound recombinant glutathione-S-transferase alone. Immunoadsorption of patient sera with fusion proteins corresponding to the G domain substantially reduced basement membrane autoantibody titers. IgG from patients with this form of cicatricial pemphigoid recognize the portion of laminin 5 thought to play a key role in promoting keratinocyte adhesion to epidermal basement membrane.