Identification of ocular cicatricial Pemphigoid antibody binding site(s) in human beta 4 integrin

PURPOSE. To identify specific site(s) on human beta4 molecule to which sera from ocular cicatricial pemphigoid (OCP) patients bind and to determine it s role in the process of blister formation. METHODS. Clone the fragments representing the extracellular and intracellul ar domain of beta4 molecule from normal human conjunctival mRNA into an exp ression vector; map the region to which sera from OCP patients bind by West ern blot analysis. Determine the role of the immunodominant region in patho genesis by demonstrating the ability of the rabbit antibody to the immunodo minant region to produce separation of basement membrane zone (BMZ) from th e basal epithelial layer when incubated with normal human conjunctiva in an in vitro organ culture model. RESULTS. Majority of the OCP sera tested bound to the C-terminal end of the intracellular domain IC3.0 of the human beta4 integrin. Further subcloning of IC3.0 demonstrated that a smaller fragment extending from 1489 aa to 15 72 aa (IC3.4) was responsible for this binding. This region may have multip le antibody binding sites. Antibody to human IC3.0 and IC3.4 produced in ra bbit, resulted in BMZ separation, histologically identical with that observ ed when normal human conjunctiva was cultured with OCP sera in an human con junctival organ culture model. CONCLUSIONS. These observations identify IC3.4 as the antibody binding site for sera of OCP patients and suggest a possible role for it in blister for mation. Indirectly it highlights certain important aspects of the structura l and functional dynamics of the biology of the hemidesmosomes and basement membranes.