IgG-rheumatoid factor in seronegative rheumatoid arthritis

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Abstract
The occurrence of IgG-rheumatoid factor (RF) reacting with rabbit IgG was studied in the sera of: a) 1105 elderly (55-74 years) males from rural areas of Finland, which were obtained in connection with a cohort study of atherosclerotic cardiovascular diseases (population series); and of b) 201 adult patients with definite or probable rheumatoid arthritis or non-definite arthritis, which were taken in connection with a follow-up (6-9 years) examination of a patient cohort with recent inflammatory joint disease (patient series). IgG-RF was measured with an enzyme-linked immunosorbent assay (ELISA) adopting a Δ-value (absorbance to antigen/antibody complex minus absorbance to antigen alone) for use. The Waaler-Rose test was positive in 28 cases (2.5 %) of the population series. Raised levels of IgG-RF (a Δ-value of ≥ 0.200) were found in 12 sera. Nine of these were positive in the Waaler-Rose test, and two further sera contained raised levels of IgM-RF as measured by latex test or by IgM-RF ELISA. The IgG-RF activity was presented at least partially in all positive sera after treatment with dithiothreitol. In the patient series, the Waaler-Rose test was positive in 58 cases (29 %). Raised levels of IgG-RF were found in 19 sera, and these were all positive in the Waaler-Rose test. Thus in our two study series raised levels of IgG-RF were almost always confined to simultaneous presence of IgM-RF. Seronegative rheumatoid arthritis was negative for IgG-RF.

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