Elevated immunoglobulin G antibodies to the proline-rich amino-terminal region of Epstein-Barr virus nuclear antigen-2 in sera from patients with systemic connective tissue diseases and from a subgroup of Sjögren's syndrome patients with pulmonary involvements.

Summary Associations of Epstein-Barr virus (EBV) and autoimmune diseases have been hypothesized. We have analysed IgG antibodies to EBV nuclear antigen (EBNA)-2 in sera from Japanese patients with autoimmune systemic connec- tive tissue diseases (CTD), exemplified by systemic lupus erythematosus (SLE), primary Sjogren's syndrome (SS), rheumatoid arthritis (RA), systemic sclerosis (SSc) and secondary SS (classical CTDs complicated with SS). An enzyme-linked immunosorbent assay (ELISA) which uses glutathione-S- transferase polypeptides fused to EBV nuclear antigen (EBNA)-2 and EBNA- 1 was developed. Ratios of IgG antibody reactivity to whole IgG concentra- tions of sera were calculated to normalize EBNA-2 and EBNA-1 antibody lev- els to the hypergammaglobulinaemia that occurs in CTD. The ELISA optical density OD 450 readings of IgG antibodies to both the amino-terminal aa 1-116 of EBNA-2 and carboxyl-terminal aa 451-641 of EBNA-1 were elevated sig- nificantly in patients with SLE, primary SS, RA, SSc and secondary SS when compared to EBNA-1. The OD readings were divided by serum IgG concen- trations to normalize for the hypergammaglobulinaemia. The specific levels of IgG antibodies to the amino-terminal region of EBNA-2 were elevated in patients with SLE, primary SS or RA, as well as those with secondary SS com- plicated with SLE or RA. The EBNA-2 amino-terminal region contains a polyproline tract and a proline-rich sequence and has considerable amino acid sequence homology with many cellular proline-rich proteins . High ratios of EBNA-2 aa 1-116 to EBNA-1 aa 451-641 IgG antibody levels which prob- ably suggest reactivation of EBV latent infection were associated significantly with pulmonary involvement in SS patients. These results are consistent with the hypothesis that the sequence similarity between the amino-terminal region of EBNA-2 and proline-rich cellular proteins is associated with patho- genesis in a subpopulation of CTD patients, possibly by the molecular mimicry-epitope shift mechanism.