Detection and measurement of rheumatoid factor using a new immunoenzyme technique with peroxidase/anti-peroxidase complex.

A new, solid-phase enzymatic technique is proposed for the detection and measurement of rheumatoid factors (RF). A complex (PAP) consisting of peroxidase and rabbit IgG anti-peroxidase antibodies was used as antigen. The sensitivity of the technique is such that even "physiological" levels of RF may be detected in the majority of serum samples. The intra-assay and inter-assay repeatability (6-8% and 12%) is better than that for either of the traditional agglutination techniques (latex fixation test and Waaler-Rose reaction, or LWR) and this means that the serological evolution of the illness may be followed more accurately for each patient. The detection of non-agglutinating RF was also possible. The antigen used (i. e. rabbit IgG) was fixed immunologically to the enzyme, hence it was not denatured by chemically labelling. This antigen resembles that of the Waaler-Rose reaction. A variation of this method enabled the detection of RF immunoglobulin class, when only the IgM fraction of the sera tested could be fixed to the solid phase by means of anti-mu F(ab')2 antibody before introduction of the antigen. The affinity constant could be measured without antibody purification. In 211 cases of adult rheumatoid arthritis, abnormally high levels of RF were revealed in 78% of the subjects using the PAP technique and in only 53% with the agglutination (LWR) techniques. On the other hand, the RF levels were within normal limits in the 51 cases of other inflammatory rheumatisms lacking RF according to LWR techniques, in 62 cases of non-inflammatory diseases (hip osteoarthrosis, low back pain) and also in the 42 cases of other inflammatory diseases.