Fig. 4. Endocytosis of Fc by IMCD cells expressing wild-type and mutant FcRn. Non-polarized IMCD cells were incubated at 37°C with ¹²⁵I-Fc with or without excess unlabeled IgG. Cell-associated CPM in the presence of competing IgG was considered non-specific and subtracted. Internal specific CPM/surface specific CPM was plotted as a function of time. Points show the means from duplicate plates from one experiment representative of three experiments. Data for wild-type FcRn are represented by open circles and mutant FcRn by filled circles in all panels, as indicated: (A) A309L/L322A/L323A, (B) L314F/L322A/L323A, (C) W311A/L322A/L323A, (D) D317A/D318A, (E) E331A/E333A.