Fig. (3) Ultrastructural features of monocyte migration through the BMVEC model of the blood-brain barrier. (A) Endothelial layer becomes thick above the pores through which the monocytes are migrating (1,000x section of the BBB model with migrating monocytes). (B) Monocytes migrate between endothelial cells and through the pore (TEM, 10,000 x).