A. Retention of ring-RBCs occurs to a similar extent in isolated human spleens and in microbeads. Mean relative ring-RBC parasitemia (100% of initial parasitemia at time 0) in the perfusate as a function of time of perfusion from 3 independent experiments. As previously observed,¹²  a fraction of ring-RBCs is retained by isolated-perfused human spleens, the initial 20-minute retention phase being followed by a plateau-phase during which the concentration of ring-RBCs in the perfusate is stable at 20% to 50% of the initial concentration (50%-80% retention). The retention rate in the isolated-perfused spleen (Δ_Spleen) was expressed as the difference between the relative ring-RBC parasitemia at T0 and at T40 (onset of plateau phase). The initial retention rate in microbeads was determined as defined in Figure 3, with a sample collected at T0 (δ_{T0 Beads}). ● represents the mean relative parasitemia downstream from microbeads. RBCs were then collected from the perfusate at different time points, allowed to flow through the microbeads, and the retention rates determined (δ_{Tx Beads}). This explored the ability of RBCs that had already crossed the spleen several times to cross the microbead layer. (B) Relative retention rate in isolated-perfused spleens and in microbeads at different time points during perfusion as observed in 3 independent experiments.