A nephelometric study of the reaction of monoclonal rheumatoid factor with heat aggregated gamma globulin and sera from patients with immune complex diseases

Monoclonal rheumatoid factors (MCRF) have previously been used in a variety of assays for the detection of IgG-containing circulating immune complexes. We have isolated a MCRF from a patient with a lymphoproliferative disorder and have used a nephelometric technique to characterize its reaction with heat-aggregated gammaglobulin (HAGG) used as a source of artificial immune complexes. The method is simple, economical and rapid and will detect as little as 6 μg/ml of HAGG over a wide range of physicochemical conditions. A clinical study demonstrated that the sera from thirty-five out of fifty-eight patients (59%) with rheumatoid arthritis and twenty-one out of seventy-four patients (28%) with systemic lupus erythematosus (SLE) gave increased precipitation with MCRF compared with 232 blood donors. However, in marked contrast to previous studies, sucrose gradient ultracentrifugal analysis of nine strongly precipitating sera revealed that in eight the MCRF precipitated with material sedimenting in the monomeric IgG position. In only one specimen did the MCRF react with material sedimenting in heavier regions. It is suggested that different MCRFs vary in the specificity for binding IgG complexes and these reagents should be carefully characterized before becoming established in nephelometric assays for circulating immune complexes.