Model of the dynamic CR1 rearrangement induced by cross-linking. In circulating erythrocytes, CR1 is likely attached to the cytoskeleton (Figure 1G), with a subpopulation interacting with FAP-1 (Figure 5A top row). Cross-linking of CR1 by either complement-opsonized beads or anti-CD35 antibodies induces the formation of large CD35 and FAP-1 clusters (Figure 5B,C). Because CD35 and FAP-1 coprecipitate in both fresh and CD35 cross-linked erythrocytes, our model depicts the CD35-FAP-1 complex in both conditions, although in the cross-linked state there are more CR1 molecules interacting with FAP-1 (Figure 5C).