© 1989 British Society for Rheumatology
research-article |
IgG RHEUMATOID FACTOR IN PURIFIED IgG FRACTIONS AND WHOLE SERA FROM PATIENTS WITH RHEUMATOID ARTHRITIS
Department of Medicine A, Rheumatology and Clinical Immunology Units, Hadassah University Hospital POB 12000, Jerusalem 91120, Israel
Correspondence to:
Correspondence to Dr. N. Harats.
There are inherent technical difficulties in measuring IgG rheumatoid factor (IgG-RF) in the serum of patients with rheumatoid arthritis (RA). These arise from measuring a reaction between two IgG molecules and the interference of IgM-RF in the reaction. We compared the prevalence of IgG-RF in whole sera and purified IgG fractions from 58 RA patients (43 of whom were latex or sheep cell agglutination positive). Methods of purification were: ammonium sulphate precipitation and DEAE cellulose or protein A-Sepharose chromatography. IgG-RF was measured by two methods: (1) radio-immunoassay and ELISA with a monoclonal myeloma IgG (IgG4,K) as the antigen and radiolabelled rabbit anti-human IgG (previously absorbed on a column with IgG4, K) as the second antibody; (2) ELISA using rabbit IgG as the antigen and a peroxidase conjugated goat anti-human IgG as the second antibody. When whole sera were assayed, 18 (31%) contained IgG-RF. In contrast, only three of the IgG fractions (5%) were positive for IgG-RF by all methods, while the remainder were uniformly negative. These results suggest that IgG-RF determination in whole sera does not accurately reflect IgG-RF activity.
KEY WORDS: Rheumatoid arthritis, IgG rheumatoid factor, ELISA, IgG subclasses