27, 34 The relevance of in vitro studies using HSECs to the situation in vivo is illustrated by the fact that many of our in vitro findings with HSECs have subsequently been confirmed by others using in vivo models. For example, the involvement of VAP-1 in lymphocyte recruitment through hepatic sinusoids was first proposed using HSECs in vitro27 and subsequently confirmed
by others using rat and mouse models in vivo.35, 36 Thus, HSECs cultured for up to four passages maintain expression of cell surface receptors that (1) define them as sinusoidal in origin and (2) allow them to interact with leukocytes during flow-based assays. We thus believe that these cells, despite losing fenestrations during passage HM781-36B concentration in culture, are appropriate to model leukocyte recruitment to the liver—particularly as this process usually occurs through damaged or inflamed sinusoids—and we refer to them as human liver sinusoidal endothelial cells (HSECs). Flow-based adhesion assays were conducted as described.37 HSECs were grown to confluence in glass capillaries for 24 hours, stimulated for 24 hours with tumor necrosis factor-α (TNF-α) selleckchem (10 ng/mL, R&D Systems) and connected to the flow-based system. In some experiments, soluble proteins were coated onto the slides, including recombinant CX3CL1 (500 ng/mL, R&D Systems), recombinant VAP-1 (1 μg/mL,
a gift from David Smith, Biotie Therapies), recombinant VCAM-1 (5 μg/mL, R&D Systems), or human albumin (1%, Sigma, Poole, UK ). CD16+ monocytes were perfused through the capillaries at wall shear stresses that mimic flow through hepatic sinusoids (0.05 Pa). Adherent cells were visualized under phase contrast microscopy and rolling, adherent (phase bright), and transmigrated cells (phase dark) quantified by offline digital analysis. The number of adherent cells was calculated as mm2/106 cells perfused. Adhesion was blocked using anti-VCAM-1 MCE (BBIG-V1), anti-ICAM-1 (BBIG-I1, R&D Systems),
anti-CX3CR1 (2A9-1, MBL, MA), anti-VAP-1 (TK8-14, a gift from David Smith, Biotie Therapies), and pertussis toxin (PTX) (Sigma, UK). Blocking reagents were incubated with HSECs or monocytes for 30 minutes and washed out before assay. Falcon transwells (24 wells/plate, 5 μm pore, Becton-Dickinson) coated on the upper membrane surface with 20% rat-tail collagen, were seeded with 5 × 104 HSECs, grown to confluence for 24 hours, and stimulated with TNF-α (10 ng/mL) for a further 24 hours. CD16+ monocytes (5 × 105) were added to the top chamber for 1.5 hours before rinsing the top well to remove nonadherent cells. After 24 hours, transmigrated cells were harvested from the bottom well, washed in PBS/BSA, and analyzed by way of flow cytometry. Hepatic mDCs were isolated from freshly explanted liver using mechanical and density gradient separation as described.
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