ICAM-3 REGULATES LYMPHOCYTE MORPHOLOGY AND INTEGRIN-MEDIATED T-CELL INTERACTION WITH ENDOTHELIAL-CELL AND EXTRACELLULAR-MATRIX LIGANDS

Leukocyte activation is a complex process that involves multiple cross -regulated cell adhesion events. In this report, we investigated the r ole of intercellular adhesion molecule-3 (ICAM-3), the third identifie d ligand for the beta 2 integrin leukocyte function-associated antigen -1 (LFA-1), in the regulation of leukocyte adhesion to ICAM-1, vascula r cell adhesion molecule-1 (VCAM-1), and the 38- and 80-kD fragments o f fibronectin (FN40 and FN80). The activating anti-ICAM-3 HP2/19, but not other anti-ICAM-3 mAb, was able to enhance T lymphoblast adhesion to these proteins when combined with very low doses of anti-CD3 mAb, w hich were unable by themselves to induce this phenomenon. In contrast, anti-ICAM-1 mAb did not enhance T cell attachment to these substrata. T cell adhesion to ICAM-1, VCAM-1, FN40, and FN80 was specifically bl ocked by anti-LFA-1, anti-VLA alpha 4, and anti-VLA alpha 5 mAb, respe ctively. The activating anti-ICAM-3 HP2/19 was also able to specifical ly enhance the VLA-4- and VLA-5-mediated binding of leukemic T Jurkat cells to VCAM-1, FN40, and FN80, even in the absence of cooccupancy of the CD3-TcR complex. We also studied the localization of ICAM-3, LFA- 1, and the VLA beta 1 integrin, by immunofluorescence microscopy, on c ells interacting with ICAM-1, VCAM-1 and FN80. We found that the anti- ICAM-3 HP2/19 mAb specifically promoted a dramatic change on the morph ology of T lymphoblasts when these cells were allowed to interact with those adhesion ligands. Under these conditions, it was observed that a large cell contact area from which an uropod-like structure (heading uropod) was projected toward the outer milieu. However, when T blasts were stimulated with other adhesion promoting agents as the activatin g anti-VLA beta 1 TS2/16 mAb or phorbol esters, this structure was not detected. The anti-ICAM-3 TP1/24 mAb was also unable to induce this p henomenon. Notably, a striking cell redistribution of ICAM-3 was induc ed specifically by the HP2/19 mAb, but not by the other anti-ICAM-3 mA b or the other adhesion promoting agents. Thus, ICAM-3 was almost excl usively concentrated in the most distal portion of the heading uropod whereas either LFA-1 or the VLA beta 1 integrin were uniformly distrib uted all over the large contact area. Moreover, this phenomenon was al so observed when T cells were specifically stimulated with the HP2/19 mAb to interact with TNF alpha-activated endothelial cells. We found t he localization of linear arrays of myosin within the heading uropod. In contrast, actin-based cytoskeleton presented a uniform distribution over the broad contact area with the substrate. In addition, butanedi one monoxime, a myosin-disrupting drug, abolished both the morphologic al cell change and ICAM-3 clustering. Altogether, these results demons trate that ICAM-3 has a regulatory role on multiple pathways of T cell adhesion and morphology.