Fig. 5. Transcytosis and recycling of Fc by wild-type and mutant FcRn. Monolayers of IMCD cells were incubated at 4°C with ¹²⁵I-Fc at either the apical or the basolateral surface. Unbound Fc was removed and the cells were warmed to initiate transport. Media at both surfaces were maintained at pH 8.0, and both sets of media were collected and counted at the indicated times. After the last time point, the cells were lysed and counted. At each time point, the cumulative Fc that underwent transcytosis or recycling was represented as a percentage of the total Fc associated with the cells. Points are means of triplicates; bars showing s.e.m. were smaller than the symbols and were omitted for clarity. Each graph is from one experiment representative of 3-7 experiments. Panels A-D show recycling to the apical surface (circles) and apical to basolateral transcytosis (downward-pointing triangles) after loading from the apical surface; panels E-H show recycling to the basolateral surface (circles) and basolateral to apical transcytosis (upward-pointing triangles) after loading from the basolateral surface. Data for wild-type FcRn are represented by open symbols and mutant FcRn by filled symbols: (A,E) A309L/L322A/L323A; (B,F) L314F/L322A/L323A; (C,G) D317A/D318A; (D,H) E331A/E333A.