Leukocyte transendothelial migration (TEM) is an essential component of the inflammatory response. In vitro studies with human cells have demonstrated that PECAM functions upstream of CD99 during TEM; however, results in vivo with mice have been apparently contradictory. In this study we use 4-dimensional intravital microscopy to demonstrate that the site and order of function of PECAM and CD99 in vivo is dependent on the strain of mice. In FVB/n mice PECAM functions upstream of CD99, as in human cells in vitro, and blocking antibodies against either molecule arrest neutrophils prior to traversing the endothelium. However in C57BL/6 mice, PECAM and CD99 appear to function at a different step, as the same antibodies arrest leukocyte migration between the abluminal side of the endothelium and the sub-endothelial basement membrane. Thus, the disparate results in the literature are due to differences in mouse strain, not experimental techniques. These results are the first direct comparison of PECAM and CD99 function in different murine strains as well as the first demonstration of the sequential function of PECAM and CD99 in vivo.
- intravital microscopy
- Copyright © 2016, American Journal of Physiology - Heart and Circulatory Physiology