The human anti-bullous pemphigoid monoclonal autoantibody P22 is encoded by genes of the IGHV4 and IGHV4 families

We identified, cloned, and biochemically characterized the full-length cDNA s encoding the heavy and light chains of a human monoclonal antibody (mAb) from the Epstein-Barr virus (EBV)-cell line P22. The cell line P22, which o riginated from a patient with bullous pemphigoid (an autoimmune disease cau sing skin blistering) expressed immunoglobulin-G (IgG) with a lambda light chain. Although the variable heavy (IGHV) chain gene family could not be as signed by IGHV repertoire analysis, the determination of its nucleotide seq uence demonstrated that the heavy chain of P22 belonged to the IGHV4 family . The limited IGHV4 gene usage by memory IgG, IGA and IgE expressing cells supports the notion of the autoreactivity-associated IGHV4 genes and stress es the strong selection pressure within germinal centres towards IGHV4 fami ly. Alignment of P22 IGHV4 cDNA sequence to germline sequences from gene da tabases, revealed a remarkable divergence, suggesting that the heavy chain of the P22 mAb encodes a distinct IGHV4 gene. The variable light chain (IGL V) encodes a IGLV4 gene and is 98% similar to a previously reported IGLV ge ne. Furthermore, fluorescent staining with the recombinant mAb showed the s ame reactivity to that of the native antibody. The data reported herein, (a ) reveal an autoantibody encoding a distinct IGHV4 gene, (b) confirm the no tion that autoantibodies preferentially use IGHV4 genes, and (c) hypothesiz e that somatic hypermutation within GC may be a mechanism by which autoreac tive B lymphocytes escape negative selection. (C) 2000 Academic Press.