| Leukocytes are initially tethered to the endothelium via selectin and selectin ligand interactions. Subsequently, the beta2 integrins play a critical role in stabilizing leukocyte rolling before arrest and firm adhesion. The overall goal of this work was to determine the roles of two of the beta2 integrins, alphaL (LFA-1) and alphaM (Mac-1), and ICAM-1, a known endothelial ligand for LFA-1 and Mac-1, in slow leukocyte rolling and arrest using their respective knockout mice and a knockin mouse whose mature myelomonocytic cells were labeled with green fluorescent protein (GFP) in vivo.; The relative roles of LFA-1 and Mac-1 and their adhesion to ICAM-1 during inflammation have been previously unclear. Using knockout and knockin mice and monoclonal antibodies (mAbs), the roles of LFA-1, Mac-1, and ICAM-1 in cytokine-induced inflammation were studied. In TNF-alpha treated cremaster muscles, the average rolling velocity in venules was slightly increased in Mac-1 -/- (5.7 mum/s) and LFA-1 -/- (5.8 mum/s) mice compared to wild-type (5.1 mum/s).; Leukocyte adhesion efficiency, a normalized parameter that relates the number of adherent leukocytes to the total number of circulating leukocytes, was similar in Mac-1 -/- (0.12 +/- 0.03 mm) and ICAM-1 null (0.11 +/- 0/01 mm) mice but significantly increased compared to LFA-1 -/- (0.08 +/- 0.01 mm) mice and significantly reduced from wild-type (0.26 +/- 0.04 mm).; Taken together, these results suggest that both LFA-1 and Mac-1 contribute to slowing down rolling leukocytes, but that the contribution of LFA-1 is more important than Mac-1. Furthermore, these results suggest that endothelial ICAM-1 is the main ligand responsible for slow leukocyte rolling mediated by Mac-1, but not LFA-1.; Lastly, in order to begin to understand if adhesion molecule knockout mice have any secondary phenotypes as related to leukocyte rolling, whole blood from a knockin mouse whose neutrophils were labeled with green fluorescent protein (GFP) (lys-EGFP) was injected into an ICAM-1null mouse. Lys-EGFP neutrophils rolled faster in ICAM-1null mice than neutrophils native to ICAM-1null mice. Furthermore, when lys-EGFP blood was transfused into a wild-type mouse, ten out of the eleven leukocytes viewed were adherent, similar to levels of adhesion seen in wild-type mice. (Abstract shortened by UMI.)... |
