Fig. 8. Two hypothetical models of DC-SIGN cluster rearward motion. (A) The constitutive transport model. DC-SIGN clusters (red border) constitutively leave the leading edge and cycle back (green border) to zones of internalization. Pathogen would be passively transported on structures undergoing this cycling. (B) The triggered transport model. DC-SIGN clusters are caught at the leading edge (red border) and must be liberated (orange border) prior to rearward transport (green border). In this model, pathogen binding would influence the probability of rearward transport of a cluster by affecting its release at the leading edge.