Fast lysis by complement and uptake by liver of avidin-carrying biotinylated erythrocytes

The fate of 51Cr-labelled avidin-carrying biotinylated erythrocytes after intravenous injection in the rat was examined. Surface amino groups of the erythrocyte membrane were modified by biotin N-hydroxysuccinimide ester. The biodistribution and stability of biotinylated erythrocytes in the blood were similar to those of non-biotinylated cells. Both types of cells circulated in the bloodstream for prolonged periods of time without substantial lysis (about 2-3% of injected radioactivity per g of blood for 24-48 hours, no more than 2% of lysis). Both types of erythrocytes were cleared by the spleen. The clearance of biotinylated cells was faster and more pronounced (peak of spleen uptake at 3 hours after injection, up to 35% of injected radioactivity per g of spleen), than that of nonbiotinylated cells (peak of spleen uptake at 24 hours after injection, up to 25% of injected radioactivity per g of spleen). Attachment of avidin to biotinylated cells results in extremely rapid lysis and clearance from the bloodstream (0.17% of injected radioactivity per g of blood 30 min after injection, 100% lysis). Radioactivity was rapidly cleared by the liver (up to 80% of injected dose per g of tissue, 70% per organ). Uptake by the spleen plays only a minor role in the clearance. Considerable lung uptake of avidin-carrying biotinylated erythrocytes was observed. Avidin-carrying biotinylated erythrocytes were lysed by fresh homologous serum in vitro in contrast to biotinylated and native cells. Lysis was eliminated by pretreatment of serum with EDTA or heating, which indicates a complement-dependent mechanism of lysis.