Serum IgG and IgM Rheumatoid Factors by Solid Phase Radioimmunoassay

Abstract

In this report, solid phase radioimmunoassays that specifically measure IgG rheumatoid factor (RF) and IgM RF in absolute concentrations are described. Polyclonal RF preparations were utilized as standards, and as little as 40 ng/ml of IgG RF and 1 ng/ml of IgM RF were detected. The IgG RF concentration of 26 seropositive rheumatoid sera was 439 ± 755 μg/ml (mean ± 1 SD), a level 107 times that of normal controls (P < 0.001). In contrast, levels for 49 children with juvenile rheumatoid arthritis (JRA) were 6.1 ± 3.7 μg/ ml for those with a polyarticular onset (JRA‐Po), 27.3 ± 113 μg/ml for the pauciarticular group (JRA‐Pa), and 12.6 ± 20.7 μg/ml for the group with a systemic onset (JRA‐S). None of these values differed significantly from the value of 6.0 ± 3.9 μg/ml measured in a juvenile control group. The IgM RF level in adult rheumatoid arthritis (RA) of 175 ± 221 μg/ml was also significantly elevated compared to controls (P < 0.001). In JRA, however, mean levels of 1.4 ± 2.0 μg/ml (JRA‐Po), 2.8 ± 8.3 μg/ml (JRA‐Pa), and 1.1 ± 0.7 μg/ml (JRA‐S) were not elevated significantly above the value of 1.2 μ 1.2 μg/ml measured in the juvenile control group. Hidden IgM RF was not found in 9 JRA sera tested. These marked differences in RF levels provide another indication that adult RA and JRA are distinct diseases.

19S IgM Rheumatoid Factor-7S IgG Rheumatoid Factor Immune Complexes Isolated in Sera of Patients with Juvenile Rheumatoid Arthritis

“…Fourth, they would not explain the IgG RF being present in the eluates. There would have to be complete cross reactivity between the anti-Fab and anti-F(ab'h antibodies and IgG RF, because in most patients with JRA IgG RF levels are> I0 ttgjml (20). Fifth, the sera of four patients with high levels of IgG in their glycine-HCl eluates demonstrated no IgG in their NH 3 or glycine-HCI eluates from the affinity column which had F(ab'h fragments of goat IgG of no immunologic specificity bound.…”

Monoclonal antibody 6b6.6 defines a cross‐reactive kappa light chain idiotope on human monoclonal and polyclonal rheumatoid factors

“…It is now clear that RF activity can be associated with IgG and IgA, as well as IgM, immunoglobulins (2-6); however, the proportions of RF isotypes expressed in different diseases or among individuals with the same disease can vary widely (6)(7)(8)(9). Similarly, RF exhibit considerable heterogeneity with respect to their interaction with IgG.…”

IgG and IgM Rheumatoid Factors in Rheumatoid Arthritis

“…33 pg/ml and 134 * 38 pg/ml, respectively. All 18 sera contained concentrations of IgM RF and IgG R F greater than 2 standard deviations above the means for a control population of normal adults (IgM R F = 1.3 5 1.0 &ml, IgG R F = 4.1 * 2.3 pg/ml, mean k SD) (19).…”