[Enzymo-immunologic determination of the class of antiglobulin factors]

The authors describe an enzymo-immunologic method of determination of the class of rheumatoid factors (RF). This technic includes 3 main stages : 1) extraction of RF by fixation on aggregated rabbit IgG previously adsorbed on the walls of a plastic tube; 2) recognition of RF linked to the solid phase by anti-IgG addition, and addition of human IgA and IgM linked to glucose oxidase; 3) revelation of the enzyme activity linked to the solid phase : this enzyme activity directly depends on the levels of RF to be estimated. The results are expressed as a percentage of the fixation of a reference serum obtained from a patient with rheumatoid arthritis (RA). This serum presents an antiglobulin activity in the 3 major classes of immunoglobulins. The coefficients of variation of intra- and intersystem reproductibility lay between 5,6 and 17.8%. The specificity of the estimation was controlled by the localisation of the antiglobulin activity of the sera after chromatography on Sephadex G200 and by estimation of RF after their absorption by an aggregated IgG immunoadsorbant. This technic was applied to the identification of RF in RA (90 cases); in diseases not related to RA and in control subjects : the sensitivity of this method appears greater than that of technics previously described (immuno-fluorescence, Rose-Waaler reaction) in fact, only 12,2% of sera of patients with RA remain negative with this new test. However, this greater sensitivity does not seem to have altered the clinical specificity of the test : in fact, only 8,4% of the sera of patients with diseases unrelated to RA are positive by this method, which, moreover, may be explained by the age of these subjects (average age 71.5 years).