Studies on the kinetics of binding of complement‐fixing dsdna/anti‐dsdna immune complexes to the red blood cells of normal individuals and patients with systemic lupus erythematosus

The kinetics of binding of prepared complement opsonized 3H-dsDNA/anti-DNA immune complexes to normal red blood cells (RBCs) and to RBCs with lowered immune complex binding capacity from certain patients with systemic lupus erythematosus (SLE) or rheumatoid arthritis was examined. Normal RBCs bound the immune complexes rapidly and reached equilibrium in about 4 minutes at 37°C, while the SLE RBCs not only bound less immune complex but required up to 30 minutes to reach equilibrium. Chemical modification of normal RBCs with moderate amounts of dithiothreitol, an agent that destroys the binding activity of the C3b receptor (CR1), produced RBCs that mimicked the equilibrium and kinetic binding properties of the SLE RBCs. These observations, taken in conjunction with a detailed examination of the temperature dependence of the binding kinetics, suggest that CR1 reorganization on the RBC surface to form binding clusters may be an essential step in the complement mediated binding of immune complexes to RBCs. The implications of these findings with respect to the clearance of immune complexes from the circulation of patients with autoimmune diseases are discussed.