IgM‐Rheumatoid Factors Cross‐reactive with IgG and a Cell Nuclear Antigen: Apparent ‘Masking’ in Original Serum

Abstract

Fourteen out of 15 Ig[immunoglobulin]M-rheumatoid factor (IgM-RF) preparations isolated from high-titered seropositive rheumatoid sera by affinity chromatography on immobilized human IgG cross-reacted with a cell nuclear antigen, as manifest by positive immunofluorescent antinuclear antibody (ANA) staining on rat liver and kidney tissue sections. The cross-reacting ANA activity within isolated IgM-RH preparations was inhibitable by human and rabbit IgG and by isolated rat liver chromatin, and could be isolated from seropositive ANA-negative sera. This cross-reacting ANA activity can apparently be masked in the original seropositive serum and may often require purification of RF from serum for its manifestation.