The passage of leukocytes through basement membranes involves proteolytic degradation of extracellular matrix (ECM) components executed by focalized proteolysis. We have investigated whether the migration of leukocytes through 3-dimensional collagenous tissue scaffolds requires similar ECM breakdown. Human T blasts and SupT1 lymphoma cells expressed mRNA of MMP-9, MT1-MMP, MT4-MMP, cathepsin L, uPA, and uPAR as well as ADAM-9, -10, -11, -15, and -17. Upon long-term migration within 3-dimensional collagen matrices, however, no in situ collagenolysis was obtained by sensitive fluorescein isothiocyanate-collagen fragmentation analysis and confocal fluorescence/backscatter microscopy. Consistent with nonproteolytic migration, T-cell crawling and path generation were not impaired by protease inhibitor cocktail targeting MMPs, serine proteases, cysteine proteases, and cathepsins. Dynamic imaging of cell-ECM interactions showed T-cell migration as an amoebalike process driven by adaptive morphology, crawling along collagen fibrils (contact guidance) and squeezing through pre-existing matrix gaps by vigorous shape change. The concept of nonproteolytic amoeboid migration was confirmed for multicomponent collagen lattices containing hyaluronan and chondroitin sulfate and for other migrating leukocytes including CD8 ؉ T blasts, monocyte-derived dendritic cells, and U937 monocytic cells. Together, amoeboid shape change and contact guidance provide constitutive protease-independent mechanisms for leukocyte trafficking through interstitial tissues that are insensitive toward pharmacologic protease inhibitors.
IntroductionThe migration and recirculation of T lymphocytes through the tissues is a multistep process that requires cell adhesion coupled with cellular strategies to overcome physical tissue barriers. 1 The principles of T-cell migration follow the paradigm of "amoeboid" movement established for the single cell state of the lower eucaryote Dictyostelium discoideum. 2,3 Amoeboid movement is a fast lowaffinity migration type driven by a roundish yet flexible cell morphology, dynamic and polarized pseudopod protrusions and retractions, which are independent of focal contact formation and stress fibers. 2 Similar to Dictyostelium, migrating T lymphocytes show an elliptoid polarized shape with a smooth yet dynamically ruffling leading edge, and an additional trailing uropod. 4 This shape generates fast (5-25 m/min) low-affinity gliding across surfaces and through 3-dimensional (3D) collagenous scaffolds 4 driven by a diffuse cortical actin cytoskeleton along the inner leaflet of the plasma membrane devoid of focal contacts at substrate interactions and stress fibers. 5,6 Amoeboid T-cell migration within extracellular matrix (ECM) occurs independently of 1 integrin-mediated adhesion both in vitro 6 and in vivo, 7 suggesting differences of the molecular basis between the movement of lymphocytes and other mobile cells, such as fibroblasts and tumor cells. 8,9 After transendothelial migration, T cells and other leukocytes ent...
