Low molecular weight rheumatoid factors in rheumatoid arthritis sera

Abstract

Low mol. wt (7S IgG) anti IgG rheumatoid factors (RE) were isolated from the serum of two patients with rheumatoid arthritis. The interaction of these RF preparations with the Fc fragment of human IgG was studies in the ultracentrifuge and compared with 19S IgM RF isolated from the same sera. The measured binding constant or IgG RF was identical to that of the IgM RF in one patient, whereas in the other patient, the IgG RF exhibited a lower binding constant than did the IgM RF.