Leukocyte transendothelial migration across vascular endothelial cells (ECs), which exist in close proximity to vascular smooth muscle cells (SMCs), is a critical step in the sequence of events leading to atherosclerosis. The early atherosclerotic lesions preferentially localize at branches and curvatures of the arterial system, where the local flow is often disturbed, suggesting that hemodynamic factors play a role in leukocyte transendothelial migration. In the present study, we investigate the effects of disturbed flow on leukocyte transendothelial migration, using our newly developed EC/SMC co-culture flow system. EC monolayers were cultured on a three-dimensional collagen gel containing multilayers of SMCs and incorporated into a vertical-step flow chamber, which can produce a disturbed flow with the patterns similar to those near arterial branches and bends, e.g., flow separation, recirculation, and reattachment. We found that co-culture with SMCs enhances leukocyte adhesion to ECs and their subsequent transendothelial migration under disturbed flow, especially in the reattachment flow area. This increase in adhesion and transmigration may be due to the adhesive and chemotactic factors released from ECs by co-culture with SMCs. Our findings have provided data for the understanding of the in vivo behaviors of leukocyte transendothelial migration under complex flow environments found in regions of prevalence of atherosclerotic lesion.
