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The conventional tests for rheumatoid factor depend upon the agglutination of particles such as red cells or latex, coated with immunoglobulin-G. Since antibodies of the IgM class tend to be particularly effective in agglutination reactions, it is likely that the rheumatoid factor tests minimize any possible contribution from antiglobulin factors in other immunoglobulin classes. However, if the rheumatoid factors represent an immunological response of the patient to slightly altered autologous IgG, one would also expect to find antiglobulin factors in the IgG and IgA classes. In order to investigate this possibility we have developed a method which identifies the immunoglobulin class of the antiglobulin and also allows a quantitative assessment to be made. The method depends upon the absorption of antiglobulins on to insoluble cross-linked rabbit y-globulin, their subsequent elution from this complex, and estimation by the immunoplate technique using specific anti-immunoglobulin antisera incorporated into the gel. A preliminary account of these studies has been revorted (Torrigiani and Roitt, 1965a).Material and Methods Sera 27 sera from patients with rheumatoid arthritis all containing rheumatoid factors reacting with rabbit IgG in the sheep cell agglutination test (SCAT) were used.As controls, 21 sera from normal blood donors and four cord bloods were tested. All sera were stored at -20°C. and spun at 4,000 r.p.m. before use.

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