Altered erythrocyte CR1 binding kinetics compensate for decreased binding capacity in rheumatoid arthritis

Patients with rheumatoid arthritis have decreased numbers of CR1 per erythrocyte and decreased binding of immune complexes to erythrocytes. Overall erythrocyte immune complex binding activity depends on both the number and the binding kinetics of CR1. We measured kinetic parameters for the interaction between a complement-containing dsDNA:anti-dsDNA probe and erythrocytes in patients with rheumatoid arthritis and normal controls. The results indicate that: 1) the maximum quantity of immune complexes bound per erythrocyte was significantly decreased in rheumatoid arthritis compared with normal controls (p less than or equal to 0.009); 2) the steady state binding constant, Kss, and the association rate constant for binding of immune complexes to erythrocytes, ka, were significantly increased in rheumatoid arthritis versus normal controls (p less than or equal to 0.0001 and 0.002 respectively); 3) the dissociation rate constant for the release of bound immune complexes from erythrocytes, kd, was slightly smaller in rheumatoid arthritis but this difference was not statistically significant; and 4) the energies of activation for the association and dissociation reactions, Eaa, and Ead, did not differ between the two groups. These data confirm that while the maximum quantity of immune complexes bound per erythrocyte is decreased in rheumatoid arthritis, the association rate constants are larger and dissociation rate constants slightly smaller than those of normal controls. Changes in these kinetic parameters compensate for the decrease in the maximum quantity of immune complexes bound per erythrocyte.(ABSTRACT TRUNCATED AT 250 WORDS)