Dendritic cells (DCs) form a key component of the immune response, as they are involved in the innate and adaptive immunity and in the process of tolerance. Under normal conditions, DCs are absent from the Central Nervous System (CNS), as the blood brain barrier (BBB) restricts their entry. However, DCs have recently been implicated in the pathogenesis of several CNS diseases. The molecular mechanisms that mediate DC trafficking across the BBB are poorly understood. The objectives of this study were to examine the role of endothelial cell adhesion molecules (eCAMs) and their ligands in the process of DC adhesion to the BBB endothelium, and to investigate the participation of DCs in human CNS diseases. To study DC adhesion, DCs were generated in vitro by culturing human blood monocytes in the presence of GM-CSF and IL- 4, and DC maturation was induced by adding inflammatory cytokines (TNF-α, IL-1β, IL-6) and PGE₂. Immature and mature DCs displayed differences in their expression of surface molecules, including eCAM ligands, by flow cytometry. Adhesion to the cerebral endothelium was investigated using an in vitro model of the BBB consisting of primary cultures of human brain microvessel endothelial cells (HBMEC). Immature or mature DCs were incubated with resting or TNF-α-activated HBMEC for up to one hour. Only a few DCs adhered to resting HBMEC, but adhesion was upregulated upon activating HBMEC (p<O.Ol). Moreover, immature DCs adhered to activated HBMEC to a greater extent compared to mature DCs (p<O.OOl). Blocking experiments indicated that the adhesion of both immature and mature DCs to HBMEC was dependent upon ICAM-1-CD18 or ICAM-2-CD18, ICAM-2-DC-SIGN, and PECAM-l PECAM-l interactions. In addition, VCAM-1-VLA-4 interactions mediated the adhesion of immature but not mature DCs to activated HBMEC. Using immunohistochemistry for DC markers, we also examined the presence of DCs in human inflammatory, infectious, and neurodegenerative diseases, stroke and tumours. The results indicate accumulation of DC SIGN—, fascin—, and MHC class Il—expressing DCs in the CNS under most pathological conditions. These findings provide further insight into the mechanisms of neuroinflammation, and highlight the role of DCs and the BBB endothelium in this process.

Dendritic cells (DCs) form a key component of the immune response, as they are involved in the innate and adaptive immunity and in the process of tolerance. Under normal conditions, DCs are absent from the Central Nervous System (CNS), as the blood brain barrier (BBB) restricts their entry. However, DCs have recently been implicated in the pathogenesis of several CNS diseases. The molecular mechanisms that mediate DC trafficking across the BBB are poorly understood. The objectives of this study were to examine the role of endothelial cell adhesion molecules (eCAMs) and their ligands in the process of DC adhesion to the BBB endothelium, and to investigate the participation of DCs in human CNS diseases. To study DC adhesion, DCs were generated in vitro by culturing human blood monocytes in the presence of GM-CSF and IL- 4, and DC maturation was induced by adding inflammatory cytokines (TNF-α, IL-1β, IL-6) and PGE₂. Immature and mature DCs displayed differences in their expression of surface molecules, including eCAM ligands, by flow cytometry. Adhesion to the cerebral endothelium was investigated using an in vitro model of the BBB consisting of primary cultures of human brain microvessel endothelial cells (HBMEC). Immature or mature DCs were incubated with resting or TNF-α-activated HBMEC for up to one hour. Only a few DCs adhered to resting HBMEC, but adhesion was upregulated upon activating HBMEC (p<O.Ol). Moreover, immature DCs adhered to activated HBMEC to a greater extent compared to mature DCs (p<O.OOl). Blocking experiments indicated that the adhesion of both immature and mature DCs to HBMEC was dependent upon ICAM-1-CD18 or ICAM-2-CD18, ICAM-2-DC-SIGN, and PECAM-l PECAM-l interactions. In addition, VCAM-1-VLA-4 interactions mediated the adhesion of immature but not mature DCs to activated HBMEC. Using immunohistochemistry for DC markers, we also examined the presence of DCs in human inflammatory, infectious, and neurodegenerative diseases, stroke and tumours. The results indicate accumulation of DC SIGN—, fascin—, and MHC class Il—expressing DCs in the CNS under most pathological conditions. These findings provide further insight into the mechanisms of neuroinflammation, and highlight the role of DCs and the BBB endothelium in this process.

Dendritic cells (DCs) form a key component of the immune response, as they are involved in the innate and adaptive immunity and in the process of tolerance. Under normal conditions, DCs are absent from the Central Nervous System (CNS), as the blood brain barrier (BBB) restricts their entry. However, DCs have recently been implicated in the pathogenesis of several CNS diseases. The molecular mechanisms that mediate DC trafficking across the BBB are poorly understood. The objectives of this study were to examine the role of endothelial cell adhesion molecules (eCAMs) and their ligands in the process of DC adhesion to the BBB endothelium, and to investigate the participation of DCs in human CNS diseases. To study DC adhesion, DCs were generated in vitro by culturing human blood monocytes in the presence of GM-CSF and IL- 4, and DC maturation was induced by adding inflammatory cytokines (TNF-α, IL-1β, IL-6) and PGE₂. Immature and mature DCs displayed differences in their expression of surface molecules, including eCAM ligands, by flow cytometry. Adhesion to the cerebral endothelium was investigated using an in vitro model of the BBB consisting of primary cultures of human brain microvessel endothelial cells (HBMEC). Immature or mature DCs were incubated with resting or TNF-α-activated HBMEC for up to one hour. Only a few DCs adhered to resting HBMEC, but adhesion was upregulated upon activating HBMEC (p<O.Ol). Moreover, immature DCs adhered to activated HBMEC to a greater extent compared to mature DCs (p<O.OOl). Blocking experiments indicated that the adhesion of both immature and mature DCs to HBMEC was dependent upon ICAM-1-CD18 or ICAM-2-CD18, ICAM-2-DC-SIGN, and PECAM-l PECAM-l interactions. In addition, VCAM-1-VLA-4 interactions mediated the adhesion of immature but not mature DCs to activated HBMEC. Using immunohistochemistry for DC markers, we also examined the presence of DCs in human inflammatory, infectious, and neurodegenerative diseases, stroke and tumours. The results indicate accumulation of DC SIGN—, fascin—, and MHC class Il—expressing DCs in the CNS under most pathological conditions. These findings provide further insight into the mechanisms of neuroinflammation, and highlight the role of DCs and the BBB endothelium in this process. / Medicine, Faculty of / Medicine, Department of / Experimental Medicine, Division of / Graduate