Cytokine-induced expression of vascular cell adhesion molecule-1 (VCAM-1) by astrocytes and astrocytoma cell lines

Astrocytes in the central nervous system (CNS) associate intimately with vascular endothelial cells and are integral to the blood-brain barrier (BBB). Leukocyte transmigration across the BBB is a cardinal feature of CNS inflammation, as observed in experimental autoimmune encephalomyelitis, and very late antigen-4 (VLA-4)/vascular cell adhesion molecule-1 (VCAM-1) interactions have recently been proposed as essential for this process. VCAM- 1 expression by astrocytes was recently reported. We addressed the regulation of VCAM-1 expression by inflammatory cytokines in primary human astrocytes and two human astrocytoma cell lines. Astrocytoma cells up-regulated surface VCAM-1 expression in response to cytokines in the following order: IFN-γ plus TNF-α > IFN-γ plus IL-1β > TNF-α > IFN-γ. Cytokine-activated astrocytoma cells expressed 7-domain VCAM-1, as indicated by accumulation of 3.2-kb VCAM-1 mRNA and immunoprecipitation of a 100-kDa protein with anti- VCAM-1 mAb. Lymphoblast adhesion to cytokine-activated astrocytoma cell monolayers was significantly blocked by mAb specific for VCAM-1 and VLA-4, indicating that astrocytoma cell VCAM-1 was functional. Astrocytoma cell expression of VCAM-1 could be a constituent of the astrocyte phenotype. To support this possibility, we demonstrated that cytokine-treated adult human and rat primary astrocytes expressed VCAM-1, and the rank order of cytokine potency for VCAM-1 induction in primary and neoplastic astrocytes was strikingly similar. This is the first documentation of VCAM-1 expression by adult human astrocytes. Expression of VCAM-1 by astrocytes at the BBB could play a role in mononuclear leukocyte entry into the CNS.