Comparison of 19.ek.Fc microspheres with mouse leukocytes
| 19.ek.Fc, μg/mL, and leukocytes . | No. of PSGL-1* . | PSGL-1 per μm2† . | Contact radius,‡μm . | Contact area, μm2 . | PSGL-1 in contact area . |
|---|---|---|---|---|---|
| 17 | 81 000 | 6 400 | 0.32 | 0.32 | 2 000 |
| 4 | 81 000 | 6 400 | 0.32 | 0.32 | 2 000 |
| 0.4 | 8 000 | 600 | 0.32 | 0.32 | 190 |
| 0.04 | 800 | 60 | 0.32 | 0.32 | 19 |
| Undeformed leukocytes | 75 000 | 400 | 0.81 | 2.0 | 800 |
| Fully deformed leukocytes | 75 000 | 200 | 3.5 | 38 | 7 600 |
| 19.ek.Fc, μg/mL, and leukocytes . | No. of PSGL-1* . | PSGL-1 per μm2† . | Contact radius,‡μm . | Contact area, μm2 . | PSGL-1 in contact area . |
|---|---|---|---|---|---|
| 17 | 81 000 | 6 400 | 0.32 | 0.32 | 2 000 |
| 4 | 81 000 | 6 400 | 0.32 | 0.32 | 2 000 |
| 0.4 | 8 000 | 600 | 0.32 | 0.32 | 190 |
| 0.04 | 800 | 60 | 0.32 | 0.32 | 19 |
| Undeformed leukocytes | 75 000 | 400 | 0.81 | 2.0 | 800 |
| Fully deformed leukocytes | 75 000 | 200 | 3.5 | 38 | 7 600 |
The number of PSGL-1 molecules on mouse leukocytes was taken from Norman et al.40 We assumed that this number represents mAb binding sites and that there are 2 binding sites per PSGL-1 dimer. Because PSGL-1 and 19.ek.Fc are dimers, the number of dimeric PSGL-1 or 19.ek.Fc molecules is about half the numbers listed.
The PSGL-1 surface density for the fully deformed leukocyte was assumed to be half that of the undeformed leukocyte due to excess membrane being exposed upon deformation. The excess membrane can cover 80% to 100% more area than that needed to envelop an undeformed leukocyte.47
The contact radius for the microspheres and undeformed leukocytes was determined using a calculation given by Cozens-Roberts et al.46 hs, the separation distance between the particle and the endothelium, was set to a minimal value of 10 nm.46 H, the maximum separation distance for receptor-ligand binding, was estimated from the length of P-selectin, 38 nm49; the length of PSGL-1, 60 nm49; and the length of 19.ek.Fc (approximately the length of IgG), 24 nm.46 H is the sum of the length of P-selectin and PSGL-1 for the leukocytes, 98 nm; and P-selectin and 19.ek.Fc for the microspheres, 62 nm. The contact radius for the deformed leukocytes is the maximal radius observed by Dong et al47 in vivo.