Effect of ECs on inducible KDR expression by human CD4⁺ and CD8⁺ T cells. Untreated or TNFα-activated ECs (100U/mL for 6 hours) were incubated with purified populations of either CD4⁺ or CD8⁺ T cells (1 × 10⁵ cells) in a ratio of 1:1 for increasing times up to 6 hours, as indicated. After coculture, FACS was performed for the evaluation of T-cell expression of KDR. (A) Representative dot plots after culture of either CD4⁺ (top panels) or CD8⁺ T cells (bottom panels) with ECs. (B) Representative FACS histograms illustrating expression of KDR on TNFα–activated ECs before and after coculture with CD4⁺ or CD8⁺ T cells. (C) Representative FACS histograms illustrating the temporal induction of KDR expression on CD4⁺ T cells (top panels) or CD8⁺ T cells (bottom panels) after coculture with TNFα–activated ECs. (D) Confocal microscopy illustrating colocalization of CD3 and KDR on CD4⁺ T cells (top panels) and CD8⁺ T cells (bottom panels) after coculture with TNFα-activated endothelial cells. Panels A, B, and C are representative of n ≥ 5 per experimental group. Panel D is representative of n = 2, with identical results.