Across the in vitro BBB model and blocking these CAMs significantly reduce disruption of the BBB model. Important observation of our data was that the WY 14643 infection of leukocytes alone was not enough to cause the disruption of the BBB model. It was the infection and subsequent activation of HBMVE cells, specifically the up regulation of these CAMs that mediated the disruption of the BBB. Additionally, our data indicate that WNV does not significantly modulate expression of VLA-4 and MAC-1 in leukocytes and this indirectly supports the notion that it is primarily the virus-induced activation of the BBB endothelium that is responsible for BBB disruption. In previous studies, avirulent strain of WNV has been shown to induce expression of ICAM-1, VCAM-1 and E-selectin in human endothelial cells, although its function in mediating leukocyte infiltration was not described. In human monocytes, this is the first report showing that WNV -induced changes in the expression of VLA-4 and MAC-1 is not as dramatic as CAMs induced in HBMVE cells. Our results using human cells partially agree with the recent mouse study demonstrating a modest increase in the VLA-4 expression in the subset of inflammatory macrophages recovered from the WNV-infected mice brain, although this increase was not significant. Further, although the infectious dose and the route of infection were different, our results in mouse brain are in accord with Dai et al., who showed increased ICAM-1 mRNA expression in the mice infected with 1000 PFU of WNV 2741 isolate via intraperitoneal route. In vivo, WNV replication is typically established in the brain of mice infected via footpad route by day 6 after infection and virus titers and WNV- induced inflammation peak by day 8 after infection. Our in vivo data demonstrating significant increase of ICAM-1, VCAM-1 and E-selectin in the brain at day 8 after infection correlates with the peak of inflammatory cytokines levels and suggest that this may be one of the downstream responses of virus-induced inflammation in the brain. Based on our in vitro data, we speculate that increased CAMs in the brain is the response of BBB-endothelial cells to WNV infection in the CNS, however likelihood of other CNS cells in contributing to CAMs increase cannot be ruled out. Robust induction of cytokines such as TNF-a and interleukin-1b is shown in WNV infected brain and it is highly likely that these inflammatory cytokines may be responsible for the induction of these CAMs as has been shown in other neuroinflammatory disorders. In order to determine the role of chemotactic gradient in leukocyte migration, we also assessed the effect of leukocyteHBMVE interaction in the presence of CCL2. CCL2 has been shown to facilitate the chemotaxis of both monocytes and T cells in vitro and has been implicated in the pathogenesis of several virus diseases including HIV, dengue and WNV. CCl2 is highly expressed in dengue hemorrhagic fever/dengue shock syndrome patients and is proposed to contribute to vascular permeability changes, possibly by weakening tight junctions of vascular endothelium cells.