Separating CD44-Mediated Monocyte Rolling from Dominant VLA-4 Adhesion

Leukocyte recruitment from blood into tissues involves sequential adhesive steps, including rolling and integrin-dependent arrest. The integrin VLA-4 is known to mediate firm adhesion, but can also support rolling. CD44–hyaluronan interactions have also been implicated in leukocyte rolling. Here, we used parallel-plate flow chamber assays to compare the contributions of CD44 and VLA-4 to monocyte rolling on different cellular monolayers. Monocytoid WEHI 78/24 cells rolled and adhered through CD44 on hyaluronan-presenting ECV304 monolayers, whereas VLA-4 dominated adhesion on endothelial monolayers expressing functional VCAM-1. Primary human monocytes showed similar CD44-dependent rolling on ECV304 monolayers. Blocking CD44, adding soluble hyaluronan, or removing surface hyaluronan with hyaluronidase reduced rolling and adhesion. These results show that CD44 can support monocyte rolling when VLA-4/VCAM-1 adhesion is not the dominant interaction. This cell-based flow model distinguishes CD44/hyaluronan-mediated rolling from VLA-4/VCAM-1-rolling and may help analyze monocyte rolling on hyaluronan, including tumor-derived monolayers.