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| Figure 4: Leukocyte extravasation due to an immune response. The entry of leukocytes into tissue due to an immune response is controlled by a cascade of molecular interactions. Upon recognition of disturbance or pathogens, resident macrophages in the affected tissue release cytokines such as IL-1, TNFα and chemokines. IL-1 and TNFα enable the endothelium of blood vessels near the site of infection to express cellular adhesion molecules, including selectins. Circulating leukocytes are localized towards the site of injury or infection due to the presence of chemokines. The selectins initiate the tethering of leukocytes to the endothelial cell surface, initiating rolling adhesion. Leukocytes roll along the blood vessel wall and sense activating chemokines which are deposited on the endothelial cell surface. This results in the activation of leukocyte integrins which bind to members of the immunoglobulin superfamily (Ig-SF) which mediate firm adhesion. This enables directed migration on the endothelial cell surface. Image courtesy of [36]. |
