A new method for the detection of hidden IgM rheumatoid factor in patients with juvenile rheumatoid arthritis.

The sera of 56 children with active seronegative juvenile rheumatoid arthritis were examined for the presence of hidden IgM rheumatoid factors (RF) by use of a rapid new method consisting of ion exchange chromatography and an ELISA assay. Elevated hidden IgM-RF levels were detected in 57% of all patients (median value 0.6 IU/ml, p less than 0.01), in 67% of patients with polyarticular disease (1.1 IU/ml, p less than 0.005), in 62% of the group with monoarticular disease (0.6 IU/ml, p less than 0.02), and in 60% of the group with systemic disease (0.6 IU/ml, NS). Whereas hidden IgM-RF plays no role in HLA-B27 positive disease, we found raised titers in 86% of B27 negative patients (0.8 IU/ml, p less than 0.001).

The comparative blood clearance kinetics of modified radiolabelled erythrocytes.

The rate of clearance from blood of 111In-labelled heat damaged autologous erythrocytes (HD-RBC) has been compared with that of simultaneously injected autologous 99mTc-labelled erythrocytes (IgG-RBC) coated with a Rhesus anti-D antibody. In 17 studies, the number of antibody molecules coating the erythrocytes was 9000 (high coating) and in nine studies the number was 5000 (low coating). On gamma camera imaging, IgG-RBC uptake, at both levels of coating, could be visualized only in the spleen. HD-RBC were predominantly taken up by the spleen, although slight 111In activity was visible in the liver. The blood clearance of IgG-RBC was monoexponential, whereas that of HD-RBC was biexponential. The reciprocal of the t1/2 (the time taken for the 3 min value to fall by 50%) of the HD-RBC clearance correlated rather poorly with the rate constant of the simultaneous IgG-RBC clearance (r = 0.47, P greater than 0.05 at high coating; r = 0.75, P less than 0.05 at low coating). The rate constant of the second exponential of the HD-RBC clearance showed a correlation with the rate constant of IgG-RBC clearance that was closer than the reciprocal of the t1/2 of HD-RBC clearance (r = 0.89, P less than 0.001 at high coating; r = 0.76, P less than 0.05 at low coating) but significantly closer only at high coating. Splenic blood flow, measured using indium labelled platelets in ten subjects, correlated closely with the initial slope of HD-RBC clearance (r = 0.93, P less than 0.001).

Evaluation of heat-damaged and IgG-coated red cells for testing reticuloendothelial function.

In vitro methods for standardising and assessing the reproducibility of reticuloendothelial function tests in man were performed. Variation in the degree of heat-induced red blood cell damage could be detected by both Channelyzer plots and a filtration test of red cell plasticity although the former test was less sensitive and difficult to quantitate. In a consecutive study of the clearance of heat-damaged red blood cells (HDRBC) in 8 patients and 2 normal individuals, consistent changes were demonstrated by both assays although occasionally one assay alone provided inconclusive results. When undamaged red cells were coated with IgG anti-D antibodies, the number of IgG molecules bound per red cell was determined by an indirect antiglobulin radioimmunoassay. With this assay, it was shown that the rate of clearance of coated cells was related to the amount of cell bound IgG anti-D. Some variation in the degree of coating of cells from patients with systemic lupus erythematosus was found although the differences were insufficient to account for the reported reduction in the clearance of IgG-coated cells in patients with this disease. The radioimmunoassay and microhaemagglutination techniques revealed that neither IgG, Clq, C3 or C3d were bound to HDRBC following incubation in autologous serum suggesting that these cells were cleared in vivo by mechanisms unrelated to immune receptor recognition.

Radioimmunoassay profile of antiglobulins in connective tissue diseases: elevated level of IgA antiglobulin in systemic sicca syndrome.

A microplate radioimmunoassay for IgG, IgA and IgM antiglobulins reactive with rabbit IgG was performed on sera from 69 patients with various connective tissue diseases. IgM antiglobulins were detected in rheumatoid arthritis, systemic sicca syndrome and some patients with systemic vasculitis. IgA antiglobulins were found in seven of 10 patients with systemic sicca syndrome and only five of 59 patients with other connective tissue diseases. There was no correlation between the levels of IgM and IgA antiglobulins in the systemic sicca syndrome or rheumatoid arthritis (r = -0.21 and 0.2 respectively). IgG antiglobulins were not detected in any serum which lacked IgM or IgA antiglobulins. IgG isolated by DEAE columns showed antiglobulin activity in six of 15 rheumatoid arthritis and two of 10 systemic sicca syndrome sera tested. Antiglobulin analysis of sera fractionated by sucrose density ultracentrifugation at neutral and acid pH enabled the size of each class of antiglobulin to be determined. In certain sera, antiglobulin activity extended into the denser region of the gradient at pH 7.2 suggesting that the antiglobulins were complexed.