Decoy receptor 3 (DcR3), a soluble receptor for FasL, LIGHT and TL1A, is highly expressed in cancer cells. We show that pretreatment of HUVECs with DcR3 enhances the adhesion of THP-1 and U937 cells and primary monocytes. A similar stimulatory effect of DcR3 on THP-1 adhesion was also observed in human microvascular endothelial cells (HMVECs). Flow cytometry and ELISA showed that DcR3-treated HUVECs exhibited significant increases in ICAM-1 and VCAM-1 expression. We also demonstrate the ability of DcR3 to stimulate the secretion of IL-8 by HUVECs. RT-PCR and reporter assays revealed that the expression of adhesion molecules and IL-8 are regulated at the level of gene transcription. Experiments with pyrrolidine dithiocarbamate indicated the involvement of an NF-kappaB signaling pathway. DcR3 was found to induce IkappaB kinase activation, IkappaB degradation, p65 nuclear translocation, and NF-kappaB DNA-binding activity. The enhancement by DcR3 of cell adhesion to HUVECs was not mimicked by the TL1A-Ab, which has been shown in our previous work to be a neutralizing Ab against TL1A, thereby inducing HUVECs angiogenesis. Moreover, DcR3-induced cell adhesion could be detected in human aortic endothelial cells (ECs) in which TL1A expression is lacking. Together, our data demonstrate that DcR3 increases monocyte adhesion to ECs via NF-kappaB activation, leading to the transcriptional up-regulation of adhesion molecules and IL-8 in ECs. This novel action appears not to be due to TL1A neutralization, but occurs through an as yet undefined target(s). This study implicates DcR3 in the relationship between inflammation and cancer development.