Abstract

This study was performed to allow the comparison of several different types of immune complex assays in patients with SLE. In performing this comparative study it was hoped to ascertain whether the Raji cell assay, the solid phase Clq binding assay and the cryoglobulins measure different sized complexes or complexes of differing composition. Initial studies on SLE patients showed that although there was a close correlation between the results of all three assays, this relationship was not absolute and several cases of Raji cell and Clq assay negativity were associated with positive cryoglobulins. Further analysis of these assays revealed that the cryoglobulins were much more reactive in the Raji cell assay than the Clq binding assay. For full reactivity however in the Raji cell assay, cryoglobulins required a fresh complement source, in particular C3. The latter phenomenon appears to be due to a loss of attached C3 during cryoglobulin preparation. Sucrose density gradient analysis of serum and cryoglobulins failed to demonstrate a difference in the size of immune complexes detected by the two assays. Immune complexes were of two sizes, small (^6.5s) and intermediate (16-19s) size, in both serum cryoglobulins. The * 6.5s immune complex predominated and along with the 16-19s material, was shown in cryoglobulins to contain DNA-anti-DNA complexes. The inability to also detect DNA-anti-DNA complexes in serum was thought to be due to technical and dilutional problems. An acid sucrose density gradient was used to try to dissociate these complexes with limited success. Intermediate sized complexes (16-19s) were acid dissociable but smaller (56.5s) complexes in sera appeared to be resistant. This may be due to the inherent resistance of small (DNA-anti-DNA) complexes to dissociation. Similarly the resistance of Raji cell and Clq binding assay reactivity to DNAase digestion does not exclude the presence of DNA-anti-DNA complexes. Using cryoglobulins, DNAase resistance was at least in part due to a protective effect of attached protein (antibody).

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