Selective antibody reactivity with peptides from human endogenous retroviruses and nonviral poly(amino acids) in patients with systemic lupus erythematosus

Objective. To investigate antibody responses to a broad panel of peptides derived from human endogenous retroviruses (HERVs) among unselected patients with systemic lupus erythematosus (SLE). Methods. In sera obtained from 69 patients with SLE and healthy blood donors, immunoassay was used to measure levels of antibody against synthetic peptides derived from HERVs, exogenous retroviruses, and nonviral poly(amino acids). Results. Measurement by immunoassay revealed increased frequencies of antiretroviral antibodies against 2 peptides derived from the env gene of the type C-like class, which includes ERV-9 and HERV-H, and against 2 peptides from the gag region of human T lymphotropic virus type I-related endogenous sequence 1, in patients with SLE. Antibodies to 2 nonviral peptides, polyhistidine and polyproline, were also overrepresented in patient sera. In 1 patient, longitudinal data obtained over a period of 12 years indicated that the concentrations of certain antiretroviral antibodies varied according to disease activity. Conclusion. Reactivity to certain type C HERV-derived antigens was found among patients with SLE. This reactivity could be explained by increased exposure to cross-reactive epitopes from essentially complete type C HERVs.