Rheumatoid arthritis is associated with the HLA antigen HLA-DR4. Disease susceptibility maps to the amino acid sequence QKRAA located in the third hypervariable region of the DR 8-1 chain. This region is thought to be a site of recognition for the T-cell antigen receptor. We searched for an antigen in the human environment that could induce T-cell recognition of this sequence. MATERIALS AND METHODS Peptides and Antibodies. The peptides used in this study were synthesized by the solid-phase method of Merrifield, modified slightly as described (7). The sequences of the peptides (p) are as follows: Dw4p, KDLLEQKRAAVDTYC; Dw14p, KDLLEQRRAAVDTYC; DwlOp, KDILEDER-AAVDTYC; gpllOp, EQNQEQKRAAQRAAGC; gpllOp short, EQKRAAQRRA. When used to raise antisera, the peptides were conjugated to keyhole limpet hemocyanin by using m-maleimidobenzoyl-N-hydroxysuccinamide ester, as described (8,9). New Zealand White rabbits were injected subcutaneously with 1 mg of conjugate emulsified in complete Freund's adjuvant and then were given booster injections three times at 3-week intervals with 1 mg of conjugate in incomplete Freund's adjuvant. The rabbits were bled 4 days after the last injection and sera were stored at -20TC. The mouse monoclonal antibody to HLA DR /3 chain was SG171 (10).Enzyme-Linked Immunosorbent Assay (ELISA). Antibody responses to the EBV glycoprotein gp110 were measured by ELISA, using the procedure developed by Luka et al. (11). Briefly, gpllO, purified by affinity chromatography from P3HR1 infected lymphoblasts (12), was used to coat ELISA plates. Various dilutions ofpreimmune or immune rabbit sera and human sera diluted in isotonic borate-buffered saline (BBS) were added in 100-,ul samples to the wells, which were incubated overnight at 4°C. After the washing with BBS/ 0.2% Tween-20, bound antibody was detected by using alkaline phosphatase-conjugated goat anti-rabbit IgG (Tago) or alkaline phosphatase-conjugated goat anti-human IgG (Boehringer Mannheim). The results are expressed as absorbance ratios, corresponding to optical densities at 405 nm for the immune serum, divided by that of the preimmune rabbit serum or by that of a serum from an EBV-negative control (11). The antibody titer for each serum was defined as the highest dilution yielding an absorbance ratio of at least 2. For inhibition experiments, peptides were added to the antisera and were allowed to react overnight at 4°C, prior to performance of the ELISA.Immunoblots. Membrane protein extracts were prepared from Molt 4 T-cell lines and from lymphoblastoid cells established from HLA-Dw4 or HLA-Dw2 homozygous donors (GM03161 and GM06821A, respectively, obtained from the Human Genetic Mutant Cell Repository, Camden, NJ), using Triton X-114 extraction according to the method developed by Bordier (13). A membrane extract from 2 X 106 cells was loaded into each lane of a 10% polyacrylamide gel containing 0.1% sodium dodecyl sulfate (NaDodSO4) and 1 mM 2-mercaptoethanol. After electrophoresis, the reduced and denatured membrane polypeptides were...

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Prior studies have shown that patients with rheumatoid arthritis (RA) have an increased number of circulating Epstein‐Barr virus–infected B lymphocytes and elevated titers of antibody to Epstein‐Barr nuclear antigen–1 (EBNA‐1), the major nuclear antigen expressed in latently infected B cells. However, it is not known whether antibodies from RA patients recognize the same epitopes as antibodies from normal subjects. Most of the anti–EBNA‐1 antibodies in normal subjects are directed at the glycine‐alanine repeating region of the molecule. Antibodies specific for this region are also somewhat more prevalent in RA patients than in normal subjects. A panel of synthetic peptides derived from EBNA‐1 was used to analyze the immune response to antigenic epitopes outside the glycine‐alanine region, using the peptides as solid‐phase antigen. Sera from RA patients and from systemic lupus erythematosus patients contained elevated levels of IgG antibodies to 2 non–glycine‐alanine peptides and to 3 non–glycine‐alanine peptides, respectively. Two of the 3 peptides are glycinerich, but antibodies that react with them are distinct from each other, as well as from those that react with the glycine‐alanine epitope. Eight other peptides from the C‐terminal portion of EBNA‐1 either do not react with sera or show no difference between normal subjects and patient groups. The antibodies to the glycine‐alanine peptide are enriched with k light chains, whereas antibodies to epitopes outside the glycinealanine region are not so restricted among k and λ light chains. Thus, RA patients and systemic lupus erythematosus patients have different antibody responses than do normal subjects, both quantitatively and qualitatively.