Clonotypic comparison of IgG anti-DNA antibodies of healthy subjects and systemic lupus erythematosus patients: studies on heterogeneity and avidity

Abstract

Qualitative characteristics of IgG anti-ssDNA antibodies were studied and compared by isoelectric focusing (IEF) and enzyme-linked immunosorbent assay (ELISA) between normal human sera (NHS) and systemic lupus erythematosus (SLE) sera. In NHS, IgG anti-ssDNA spectrotypes were observed in a high alkaline pH range (7.5 to 8.5) at physiological NaCl concentrations (0.15 M). In SLE sera the spectrotypes were found to a more intensified extent in the alkaline pH range as compared to those in NHS. With regard to avidity, analyzed by salt-dependent changes of anti-ssDNA activities, NHS showed strong ssDNA-binding bands in a wide range of pH 7.0–8.5 comparable to those in SLE sera. However, these bands became extremely weak and/or faint in pH 7.5–8.5 as the NaCl concentration was raised to 0.15 M and 0.20 M. On the other hand, SLE sera still exhibited thick binding bands at higher NaCl concentrations. This salt-dependency of these antibodies was also demonstrated by ELISA of serum samples adjusted to contain comparable antibody levels. These findings suggest that clonotypes of IgG anti-ssDNA antibodies both in NHS and in SLE sera are essentially oligoclonal and highly cationic, and that the distinctive characteristics of these antibodies in NHS may be of low avidity, in contrast to SLE sera which exhibit high avidity.