Antibody reactivity to the hres‐1 endogenous retroviral element identifies a subset of patients with systemic lupus erythematosus and overlap syndromes

Abstract Objective. To evaluate the correlation between the presence of antibodies to an endogenous retroviral element–encoded nuclear protein autoantigen, HRES‐1, and the presence of other antinuclear antibodies and HLA class II alleles in patients with systemic lupus erythematosus (SLE) and overlap syndromes. Methods. Antibody reactivities to native and recombinant proteins and synthetic peptides were assessed by counterimmunoelectrophoresis, enzyme‐linked immunosorbent assay, and Western blotting. HLA class II alleles were determined by oligonucleotide typing. Results. Forty‐eight percent of the 153 patients with autoimmune disease, and 52% of the subgroup with SLE, had HRES‐1 antibodies. In contrast, 3.6% of 111 normal donors, and none of 42 patients with the acquired immunodeficiency syndrome or 50 asymptomatic human immunodeficiency virus 1–infected patients, had HRES‐1 antibodies. Chi‐square analyses revealed a significant association between anti–HRES‐1 and anti‐RNP and an inverse correlation between HRES‐1 and Ro/La autoantibodies in patients with SLE or overlap syndromes. Antigenic epitopes of HRES‐1 and the retroviral gag–related region of the 70‐kd protein component of U1 small nuclear RNP, which share 3 consecutive highly charged amino acids (Arg‐Arg‐Glu), an additional Arg, and functionally similar Arg/Lys residues, represent cross‐reactive epitopes between the two proteins. Selective removal of HRES‐1 antibodies from sera of HRES‐1‐seropositive/RNP‐seropositive patients by absorption on recombinant HRES‐1/glutathione‐ S ‐transferase‐conjugated agarose beads had no effect on anti‐RNP reactivities. A comparative multivariate analysis of HLA class II genes revealed a differential segregation of DQB1 alleles in HRES‐1‐seropositive versus HRES‐1‐seronegative patients ( P = 0.04). While a relative increase of DQB1*0402 among HRES‐1‐seropositive patients was noted across ethnic groups ( P = 0.02), a decrease of DQB1*0201 and DQB1*0301 was found in white HRES‐1‐seropositive patients ( P = 0.04). Conclusion. Autoantibodies to HRES‐1 are detectable in a distinct subset of patients with autoimmune disease, primarily in those who do not have antibodies to Ro and La. Anti–HRES‐1 and anti‐RNP reactivities are mediated by cross‐reactive but separate antibody molecules. HLA–DQB genes, rather than HLA–DRB or DQA genes, may have a more significant influence on generation of these antinuclear autoantibodies.