The 19.ek.Fc microspheres exhibit greater adhesion than ek.Fc microspheres in vivo.

Murine cremaster muscle was exteriorized and prepared for observation. A suspension containing equal numbers of 19.ek.Fc and ek.Fc microspheres was prepared and injected. A segment on the postcapillary venules was imaged under illumination that allowed detection of (A) the 19.ek.Fc microspheres or (B) the ek.Fc microspheres. A significantly greater number of adherent 19.ek.Fc microspheres were observed compared with the number of ek.Fc microspheres. The flow of microspheres through the microvasculature is not continuous in time. In particular, there are short periods of time when few or no microspheres are observed to pass through a particular vessel. For clarity, we chose such images to generate this figure. Thus, there is only one nonadherent microsphere passing through the vessel (the “streak” at the bottom of panel A). These images were taken toward the end of an experiment when most of the adherent microspheres are firmly adherent.