CD44–Hyaluronan-Dependent Monocyte Rolling

Leukocyte recruitment from blood into tissues involves sequential adhesive steps, including rolling and integrin-dependent arrest. VLA-4 can support firm adhesion and, in some settings, rolling interactions, whereas CD44–hyaluronan interactions have also been implicated in leukocyte rolling. Here, we used adhesion assays and parallel-plate flow chamber experiments to analyze CD44–hyaluronan-dependent monocyte interactions on ECV304 monolayers and to compare them with α4-integrin-sensitive adhesion on endothelial monolayers. WEHI 78/24 monocytoid cells interacted with ECV304 monolayers in a CD44- and hyaluronan-dependent manner, whereas adhesion to HMEC-1 and bEnd.3 monolayers was sensitive to α4-integrin blockade. Blocking CD44, adding soluble hyaluronan, or treating ECV304 monolayers with hyaluronidase reduced adhesion and rolling. Mixed primary human monocyte preparations also showed CD44-dependent adhesion and rolling on ECV304 monolayers. ECV304 cells are interpreted here not as endothelial cells, but as T24-derived, hyaluronidase-sensitive cellular monolayers useful for functional analysis of CD44–hyaluronan-dependent interactions. These findings support a substrate-dependent functional hierarchy in which CD44–hyaluronan-dependent monocyte rolling becomes detectable when α4-integrin-dependent adhesion is not dominant, while emphasizing the cell-model-based nature of the assay.