The adhesion of 19.ek.Fc microspheres appears to occur via endothelially expressed P-selectin and the PSGL-1 portion of the 19.ek.Fc construct.

(A) Murine cremaster muscle was exteriorized and prepared for observation. The 2 μm 19.ek.Fc or ek.Fc microspheres were injected into the jugular vein, and the number of rolling microspheres per vessel per time was determined within 2 minutes after injection of the microspheres. In certain cases the microspheres or the mice were pretreated with mAbs. A significantly greater number of 19.ek.Fc microspheres were rolling compared with the number of ek.Fc microspheres. The number of rolling 19.ek.Fc microspheres were significantly reduced by pretreatment of the microspheres with an anti–PSGL-1 mAb or pretreatment of the mice by an anti–P-selectin mAb. (B) The number of firmly adherent microspheres per venule were determined 3 minutes after injection. Trends similar to that observed for the rolling microspheres were also observed for the firmly adherent microspheres. Ligand indicates which molecule was on the microsphere; mAb, pretreatment of the microsphere or mice with the indicated mAb. KPL-1 is an antihuman PSGL-1 mAb used on the microspheres. RB40.34 is an antimouse P-selectin mAb, and 3E2 is an antimouse ICAM-1 mAb used on the mice; n ≥ 3; *P < .01.