Table 1.
The affinity of human CD47 is much higher for signal-regulatory protein-α (SIRPα) from NOD mouse compared with that from other strains tested (P < 0·05, Mann–Whitney U-test)
| Human CD47 | Mouse CD47 | ||||||
|---|---|---|---|---|---|---|---|
| KD (μm) | SD | n | KD (μm) | SD | n | ||
| Human SIRPα | V2 3d | 0·6 | 0·12 | 4 | > 30 | ||
| Mouse SIRPα | NOD WT d1 | 0·08 | 0·02 | 4 | 4·7 | 0·41 | 4 |
| NOD + SE d1 | 9·4 | 1·22 | 4 | 11·8 | 1·53 | 3 | |
| NOD + SE 3d | 7·6 | 1·22 | 4 | 8·6 | 1·27 | 3 | |
| C57BL/6 d1 | 5·2 | 0·8 | 4 | 5·3 | 1·61 | 3 | |
| 129 3d | 5·8 | 1·13 | 4 | 2·5 | 0·26 | 3 | |
The affinities of the interactions of human and mouse CD47 with SIRPα from human and various mouse strains were determined by BIAcore analysis at 37° (Fig. 2). In some cases affinity was determined using all three extracellular domains of SIRPα (designated 3d) and in others the N-terminal domain alone (d1). (All the CD47 binding is associated with the N-terminal domain of SIRPα).19 The NOD + SE indicates a mutant in which SerGlu was inserted at the position where these residues are found in most mouse strains apart from NOD (Fig. 1). The results are from three or four independent experiments.