Table 1.

Binding affinities of the humanized Fcs for human and mouse FcRn at pH 6.0

	Human FcRn				Mouse FcRn
	Wild-type Fc (nM)		T250Q/M428L Fc (nM)		Wild-type Fc (nM)		T250Q/M428L Fc (nM)
	Kd1	Kd2	Kd1	Kd2	Kd1	Kd2	Kd1	Kd2
Texas-Red labeled	100 ± 8 (85)	9 ± 0.3 (15)	7.5 ± 0.6 (92)	2.0 ± 0.2 (8)	10.6 ± 0.7 (93)	4.5 ± 1.7 (7)	2.5 ± 0.4 (96)	0.7 ± 0.2 (4)
Unlabeled	80 ± 3 (87)	17 ± 4 (13)	1.9 ± 0.3 (95)	3 ± 1 (5)	3.2 ± 0.2 (91)	0.5 ± 0.1 (9)	0.4 ± 0.01 (94)	0.2 ± 0.1 (6)

K_dvalues are mean ± SD as determined in three separate binding experiments, with percent shown in parentheses. The percent values represent the percent population of Fc–FcRn complexes for each K_d value, as determined by the heterogeneous binding model.