Soluble complexes and antiglobulin factors detection by immunofluorescence and immunoadsorption in rheumatoid sera

In this report is was demonstrated that in rheumatoid factors (RF) positive sera, 19 S IgM rheumatoid factor can form soluble complexes with different proteins (IgG, albumin) of sera. In these complexes the antiglobulin activity of IgM is not inhibited. When immunofluorescence and immunoadsorption procedures are used for the detection of antiglobulin activities of rheumatoid sera, the proteins which are bound to IgM rheumatoid factor, even if they are devoid of any antiglobulin character, may be revealed simultaneously with IgM. Moreover in some cases the detection of IgM may be hindered, while the linked proteins remain detectable. In these conditions, these complexes in RF positive sera may give false negative results for IgM rheumatoid factor, and may give rise to artefactual appearance of IgG and other proteins (albumin antiglobulin-like activities. This paper points out that before investigating IgG and IgA antiglobulin activities, IgM rheumatoid factor should be previously eliminated, for example by immunoadsorption.