Table 1.

Summary of ESK1 and ESKM binding to mouse and human FcγRs, and RMF/A2+ target cells

Kd ± SD (nmol/L)
ReceptorESK1ESKMRatio of affinity constants (ESKM/ESK1)
Mouse
 FcγRIIb32.0 ± 0.45462.3 ± 7.270.51
 FcγRIV3.34 ± 0.1932.21 ± 0.1531.51
Human
 FcγRI0.581 ± 0.1130.680 ± 0.125N.C.
 FcγRIIa105 ± 15.558.3 ± 8.801.81
 FcγRIIb1338 ± 2532644 ± 4380.51
 FcγRIIIa (158V)92.6 ± 15.050.4 ± 8.351.84
 FcγRIIIa (158F)19.0 ± 2.385.53 ± 0.7413.45
 FcRn824 ± 102780 ± 97.5N.C.
Cell line
 JMN0.20.4

NOTE: Anti-mouse FcR binding was assessed by ELISA, whereas anti-human FcR binding was determined by FCM titration on FcγR-expressing CHO cells. N.C., no change. To determine affinity for the RMF/A2 epitope, 125I-labeled ESK1 and ESKM mAbs were titrated against JMN cells. All curves were fit with a nonlinear single-site total binding saturation curve, and Kd was calculated using Prism software.