Fig. 1

Schematic of the hypothesis for efficient FcRn-mediated recycling. Administered therapeutic IgG antibodies compete with endogenous IgG for limited hFcRn in the endosome. Effective recycling requires therapeutic antibodies to exhibit accelerated hFcRn binding at acidic pH (5.5–6.0) and rapid dissociation at neutral pH, enabling escape from lysosomal degradation, efficient recycling, and prolonged serum persistence