t-PA acts as a cytokine to regulate lymphocyte-endothelium adhesion in experimental autoimmune encephalomyelitis

•t-PA enhances T cell adhesion to, and migration across, vascular endothelial cells.•t-PA increases ICAM-1 expression in vascular endothelial cells.•t-PA affects T cell-vascular endothelial cell adhesion by acting as a cytokine.•t-PA administration induces an early onset and increased severity of EAE.

In this study, the capacity for t-PA to affect T cell-brain microvascular endothelial cell adhesion by acting as a cytokine was investigated. Following the treatment of a brain-derived endothelial cell line, bEnd.3, with various concentrations of t-PA, adhesion and transwell migration assays were performed. In the presence of t-PA, enhanced adhesion of T cells to bEnd.3 cells was observed. Using western blot analysis, an increase in ICAM-1 expression was detected for both t-PA-treated bEnd.3 cells and bEnd.3 cells treated with a non-enzymatic form of t-PA. In contrast, when LRP1 was blocked using a specific antibody, upregulation of ICAM-1 was inhibited and cAMP-PKA signaling was affected. Furthermore, using an EAE mouse model, administration of t-PA was associated with an increase in ICAM-1 expression by brain endothelial cells. Taken together, these findings suggest that t-PA can induce ICAM-1 expression in brain microvascular endothelial cells, and this may promote the development of EAE.