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Adhesion of leukocytes to endothelial cells under conditions of blood flow
Figure 2. Adhesion of leukocytes to endothelial cells under conditions of blood
flow. (a) Primary adhesion. Free-flowing leukocytes in the circulation are
captured by tethering or rolling receptors (such as E-selectin; shown here in
green) expressed on endothelial cells. (b) Triggering. Once captured, chemokine
signals (orange) localised to the lumenal side of the endothelial surface are
detected by specific G-protein-coupled receptors (red) expressed on the leukocyte.
(c) Arrest. This results in a conformational change in leukocyte integrin molecules
(light blue), which are converted to a high-affinity state, permitting firm
adhesion to immunoglobulin adhesion molecules (dark blue) expressed by endothelial
cells. (d) Transendothelial migration. Chemokine recognition also results in
cytoskeletal reorganisation within the adherent leukocyte, which facilitates
migration across the endothelial monolayers and into tissue. The molecules that
mediate migration have not been precisely defined but are likely to be members
of the integrin and immunoglobulin families. Once within the tissue, the leukocyte
follows a chemotactic gradient of chemokine signals towards the site of inflammation
(fig002dab).
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