Vascular endothelial cells (ECs) are exposed to shear stress and the neighboring smooth muscle cells (SMCs) in vivo.We studied the interaction between ECs with SMCs (synthetic phenotype) in vitro in a flow system.Co-culture under static condition induced rapid and sustained increases in the expression of E-selectin and the nuclear factor-κB (NF-κB)-promoter binding activity in ECs.Inhibition of NF-κB activation blocked the co-culture-induced E-selectin promoter activity.Studies with protein arrays and neutralizing antibodies showed that the IL-1β and IL-6 produced by SMCs are the major contributors to the co-culture-induction of EC E-selectin expression, which is inhibited by exposing ECs to laminar shear stress.