IgA and IgM Rheumatoid Factors as Markers of Later Erosive Changes in Rheumatoid Arthritis (RA)

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Abstract
Stored samples from within the first year of disease of 119 patients with rheumatoid arthritis (RA) enrolled in a long-running prospective study have been studied for the presence of IgM and IgA rheumatoid factors (RF), using agglutination of rabbit IgG-coated red blood cells to detect IgMRF and an ELISA technique using rabbit IgG coated on the microtitre plates and labelled F(aB)2 fragment of goat anti-IgA. Outcome measures at a mean follow-up of 10.1 years (range 3-20) included the Steinbrocker functional grade and grading of erosive changes on hand and feet Xrays using a modification of Lawrence's method. Both IgA and IgG levels at presentation correlated significantly with outcome measured by erosive changes and functional grade at a mean of 10 years and with the time of first appearance of erosions. In patients who are IgMRF negative early in the disease, IgARF positivity indicates a greater chance of developing both erosions and impaired function than when both tests are negative. IgARF positivity seems to precede IgMRF.