Table 2.

Binding of CR1 to C4b.

Affinity to C4b Dimer (nM)	Affinity to C4b Monomer (nM)	Method Used	CR1 Source	References
12 a	>100-fold weaker b	Radioligand binding/competition	sCR1 and E-CR1	Wiesman et al., 1990 [24]
340	>100-fold weaker b	Radioligand binding assay	E-CR1	Reilly et al., 1994 [36]
360	>100-fold weaker b	Radioligand binding assay	Expressed on CHO cells	Reilly et al., 1994 [36]
120–480 c	Not measured	Radioligand binding assay	E-CR1	Reilly and Mold 1997 [40]
330–390 d	900	SPR	sCR1	Clemenza and Isenman 2004 [38]

^a Affinity estimate based on the concentration of sCR1 needed for 50% inhibition of C4-ma (C4b-like) binding to E-CR1. ^b Compared to dimer. ^c Affinity of CR1 to C4b dimer (A isoform) measured at 120–140 nM; affinity to C4b dimer (B isoform) measured at 410–480 nM. ^d In total, 13% of the binding sites were determined to be of high affinity (8–12 nM). E-CR1: erythrocyte-expressed CR1. CHO: Chinese hamster ovary. SPR: surface plasmon resonance.