Fig. 6. Photomicrographs of planar cultures of isolated MPCs (A-E) and endothelial cells (F), and of histologic sections of native rat aorta (G,H) immunostained for Tie2 by immunoperoxidase (A,B,F-H) or immunofluorescence (C-E). Planar cultures: (A) shows a group of confluent MPCs whereas (B) shows a single MPC at higher magnification. Immunoperoxidase staining of cultured cells demonstrated Tie2 in both MPCs (A,B) and control endothelial cells (F). The positive staining reaction for Tie2 was predominantly localized at the cell periphery (arrows). Confocal images of MPCs double stained for Tie2 (C, green fluorescence) and -SMA (D, red fluorescence) showed coexpression of Tie2 and -SMA in the same cells (E, green and red fluorescence overlay). Cultured cells reacted with nonimmune IgG were negative (data not shown). Scale bars, 50 µM (A,C-E), 30 µM (B,F). Histological sections of native rat aorta: the intimal and subintimal layers of the aorta contain Tie2⁺ nonendothelial mesenchymal cells (G,H, arrows). Arrowheads highlight the endothelial lining of the aortic intima, which serves as a positive internal control. Scale bar, 100 µm.

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