Figure 1: Beta2-integrin functions in the immune system. Beta2-integrins are critical to many functions inthe immune system. Complement receptors 3 and 4 (Mac-1 and CD11c/CD18) mediate phagocytosis of complement opsonized particles, and are important for theclearance of immune complexes and apoptotic cells. Binding of beta2-integrins on T cells to ICAM-1 on dendritic cells strengthens thecell-cell interaction and contributes to T cell activation. Beta2-integrin outside-in signalling in macrophages dampens TLR signalling and inflammatory cytokine production. The binding of leukocyte integrins to ICAM ligands expressed on endothelial cells arrests leukocytes at sites of inflammation and precedes extravasation into surrounding tissue.