[Effect of rheumatoid factors on results for determination of antitoxoplasms IgM antibodies by immunofluorescence and agglutination technics (author's transl)].

Simultaneous presence of antitoxoplasm IgG antibodies and of rheumatoid factors gives rise to an IgM-type immunofluorescence reaction in 44 p. cent of cases. Three experiments showed that association of the two antibodies can give rise to false positives in the Remington test ; the mixture of the two antibodies renders the reaction positive in the majority of cases. On the other hand, after absorption of negative rheumatoid factors and separation of serum IgM and IgG, IgM fluorescence is no longer seen ; if they are again mixed, then a positive reaction will result. Interference of antitoxoplasm IgG antibodies and rheumatoid factors does not occur in direct toxoplasm agglutination tests. The presence of the rheumatoid factor is rare in the pregnant female. Nevertheless, it is necessary to test for rheumatoid factors using the latex test. If results are here positive, then serum should be absorbed on aggregated human IgG and the Remington test repeated. The probably rare simultaneous presence of antitoxoplasm IgG antibodies and of rheumatoid factors cannot be differentiated from these false positives without fractionation of the serum, separating IgM and IgG.