The autoantibodies to alpha(6)beta(4) integrin of patients affected by ocular cicatricial pemphigoid recognize predominantly epitopes within the large cytoplasmic domain of human beta(4)

This study was undertaken to characterize the antigenic determinants recogn ized by the autoantibodies of patients with ocular cicatricial pemphigoid ( OCP), OCP is a subepithelial, blistering, autoimmune disease that mainly af fects the conjunctiva and other mucous membranes. We previously demonstrate d that a cDNA clone, isolated from a keratinocyte expression library by usi ng immunoaffinity-purified OCP autoantibody, encoded the cytoplasmic domain of beta (4) integrin subunit, Our subsequent studies showed that sera from all the OCP patients that were tested recognize the human beta (4) integri n subunit, To identify the prevalent epitopes of the anti-beta (4) autoanti bodies of OCP, we have used cell lines transfected with vectors encoding a wild-type beta (4) subunit, a tailless beta (4) subunit, or a beta (4) subu nit lacking the extracellular domain. Nontransfected cell lines were used a s controls. Lysates from these cell lines were analyzed with OCP sera, IgG fractions from OCP sera, and immunoaffinity-purified OCP autoantibodies. Ab s to extracellular and cytoplasmic domains of human beta (4) integrin were used as positive controls, whereas normal human sera and normal human IgG f ractions were used as negative controls. The reactivity of OCP Abs was dete rmined by using immunoblotting, immunoprecipitation, and FAGS analysis. The results of this study indicate that OCP sera, OCP Ige fractions, and immun oaffinity-purified OCP autoantibodies react with the intracellular and not the extracellular domain of human beta (4) integrin subunit. In vitro cell culture experiments demonstrated that OCP autoantibody binds to the cytopla sm of the cells. The relevance of these findings to the pathogenesis of OCP is discussed.