The efficient trafficking of immune cells into peripheral nonlymphoid tissues is key to enact their protective functions. the endothelium. Additionally, these cells deposit CD18+ microparticles at the subendothelial layer before retracting the stretched uropod. Experiments with knockout mice and blocking antibodies reveal that the uropod elongation and microparticle formation are the result of LFA-1Cmediated adhesion and VLA-3Cmediated cell migration through the vascular basement membrane. These findings suggest that uropod elongation is a final step in the leukocyte extravasation cascade, which may be important for precise regulation of leukocyte recruitment into inflamed tissues. The maintenance of homeostatic immune surveillance and the development of protective immune responses require that leukocytes efficiently cross tissue barriers and traffic throughout the body, moving in and out of the bone marrow and through lymphoid and nonlymphoid tissues under both normal and infected or inflamed conditions (von Andrian and Mackay, 2000). The conventional multistep paradigm in leukocyte extravasation consists of a cascade of events, including tethering and rolling interactions of leukocytes on the endothelial surface (step 1), leukocyte activation by the local chemokines and/or other inflammatory signals resulting in the activation of integrin adhesiveness (step 2), and the firm adhesion of leukocytes to the blood vessel wall (step 3). The entire process is then followed by crawling and transendothelial migration (TEM), by which leukocytes leave the blood stream and enter the site of inflammation (Nourshargh et al., 2010). The CD18 integrins (also known as 2 integrins), which include LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18), are central components of this process. The CD18 integrins are expressed on the surface of most leukocytes and play a major role in regulating leukocyte adhesion and recruitment to damaged or infected tissues during inflammation. Although leukocyte recruitment is key for the host defense against infection and injury, the deregulation and/or massive infiltration of active leukocytes could damage the vasculature and underlying tissues. Indeed, leukocyteCendothelial interactions and cell emigration are crucial events that lead to plasma leakage and organ dysfunction. However, studies using in vivo (Zeng et al., 2002) and in vitro (Huang et al., 1988; Burns et al., 1997) models have suggested that little change occurs in vessel and endothelial cell barrier PH-797804 function during the transmigration of leukocytes. These studies suggest the presence of mechanisms that uncouple leukocyte transmigration from endothelial barrier function for macromolecular transport (He, 2010). Endothelial Mouse monoclonal to CD54.CT12 reacts withCD54, the 90 kDa intercellular adhesion molecule-1 (ICAM-1). CD54 is expressed at high levels on activated endothelial cells and at moderate levels on activated T lymphocytes, activated B lymphocytes and monocytes. ATL, and some solid tumor cells, also express CD54 rather strongly. CD54 is inducible on epithelial, fibroblastic and endothelial cells and is enhanced by cytokines such as TNF, IL-1 and IFN-g. CD54 acts as a receptor for Rhinovirus or RBCs infected with malarial parasite. CD11a/CD18 or CD11b/CD18 bind to CD54, resulting in an immune reaction and subsequent inflammation cells form a transmigratory cup, which is a membrane projection enriched with ICAM-1 and VCAM-1 that surrounds adherent leukocytes on the apical side of the endothelium (Carman and Springer, 2004). Emigrating leukocytes are then encapsulated in endothelial domes to minimize increases in vascular permeability (Phillipson et al., 2008). During the procedure, leukocyte LFA-1 and endothelial ICAM-1 remain bound and are redistributed together to form a distinct ring-like structure, which is maintained until TEM is complete (Shaw et al., 2004). After TEM and before approaching the interstitial area, leukocytes must detach their tails from the basolateral side of the endothelial layer and/or basement membrane. Thus, leukocyte tail detachment is PH-797804 considered to be a final step in the completion of leukocyte extravasation, although it is not clear how this event occurs. The functions of the CD18 integrins have been studied using monoclonal antibodies and small-molecule inhibitors that block integrin-mediated adhesion as well PH-797804 as gene-deficient mice that do not express integrins or their ligands. Given the importance of the dynamic regulation of integrin activation during leukocyte migration, simple loss-of-function approaches are not sufficient to gain an understanding of integrin biology in vivo. Despite recent advances in studies concerning leukocyte migration and trafficking in lymphoid and nonlymphoid tissues, the visualization of endogenous cell surface molecules on intact tissues has been challenging (Bonasio et al., 2007; Friedman et al., 2010). In this study, we generated a knockin (KI) mouse in which CD18 is fused with monomeric CFP (mCFP). With enhanced three-dimensional detection and extended in vivo z-series sections using multiphoton intravital microscopy (MP-IVM), we report that extravasating leukocytes (neutrophils, monocytes, and effector T cells) at the tissue site show delayed uropod detachment and become extremely elongated before the completion of transmigration across the endothelium. Surprisingly, these cells deposit CD18+ microparticles at the subendothelial layer while retracting the stretched uropod. RESULTS Generation of KI mice in which CD18 is fused with.