Immunoglobulin G subclass of human antinuclear antibodies.

Fourteen sera containing antinuclear antibodies were studied to determine whether the immunoglobulin G subclass of these antibodies correlated with the relative complement fixing activity of the antibodies or the presence or absence of lupus nephritis. Sera studied included eight with high complement fixing activity, all from patients with active lupus nephritis and six with low complement fixing activity, three from patients with lupus without nephritis and three from patients with antinuclear antibodies induced by procainamide. Purified antinuclear antibodies reactive with desoxyribonucleoprotein and desoxyribonuclease were prepared by elution, and subclass typing was carried out by radial immunoassay with specific antisera. In general, subclasses represented were similar in frequency to the occurrence of the subclasses in normal immunoglobulin G. There was no striking predominance or absence of any single subclass which might correlate with presence of nephritis, or differing complement fixing activity of sera. There was a trend to a predominance of subclasses high in complement fixing activity in antinuclear antibodies from lupus patients with active nephritis and subclasses low in complement fixing activity from those without nephritis.