Functional characterization of non-human primate erythrocyte immune adherence receptors: implications for the uptake of immune complexes by the cells of the mononuclear phagocytic system.

Erythrocytes from primates express an immune adherence (IA) receptor that binds complement-opsonized immune complexes (IC) both in vivo and in vitro. We have analyzed the immunochemical and functional properties of the IA receptor from erythrocytes from species that have been used for in vivo IC clearance studies and have compared these properties to the human IA receptor (which is called complement receptor type 1, CR1). Erythrocytes from all species (chimpanzee, baboon, rhesus and cynomolgus monkey) bind antibody/double-stranded DNA IC when opsonized with autologous complement. However, IC which are bound to chimpanzee erythrocytes are not released upon addition of chimpanzee serum (which contains factor I activity), while IC bound to baboon erythrocytes and human erythrocytes are released upon addition of autologous serum. Anti-human CR1 monoclonal antibodies (mAb) E11 and HB8592 bind to erythrocytes from all species examined and the number of mAb epitopes per erythrocyte correlated with the number of IC that could bind to the erythrocyte under saturating conditions. However, a number of interesting differences between the species are observed with other mAb. The anti-CR1 mAb 1B4 and 3D9, which block recognition of ligand by CR1, did not bind to chimpanzee erythrocytes and bound partially to rhesus and cynomolgus monkey erythrocytes. In addition, the ability of autologous serum to induce release of erythrocyte-bound IC correlates with the presence of these epitopes. These findings, taken in context with previous clearance studies, suggest that serum-mediated release may not be required for the rapid transfer of the IC from the erythrocyte to the mononuclear phagocytic system.