ELISA estimations of rheumatoid factor IgM, IgA, and IgG in sera from RA patients with high disease activity. DTT treatment studies

Although Elisa assays detecting rheumatoid factor's (RF) show high sensitivity and specificity, difficulties with IgA- and especially IgG-RF testing in ELISA systems, due to interaction from 'contaminating' IgM-RF is still thought to be a problem. Sera from 15 Rheumatoid Arthritis patients with high disease activity and high IgM-RF values were Dithiothreitol (DTT) treated. IgM-RF values were reduced to approximately zero in all tested sera. IgA-RF activity declined as expected, but also showed a statistically significant correlation between % reduction after DTT treatment and the IgM-RF value from the same serum sample. IgG-RF also decreased after DTT treatment, most pronounced for high IgG-RF values. A correlation (not statistically significant) between the % reduction in IgG-RF after DTT treatment and the IgM-RF value from the same serum sample was observed. Pepsin and Diethylammonium ethyl (DEAE) reduced the IgG-RF activity even more than after DTT treatment of the sera. Fractionation by Gel filtration of 8 serum samples showed that all the RF activity were found according to the 'first top' of the gel filtration curve.