Ly-6C regulates endothelial adhesion and homing of CD8(+) T cells by activating integrin-dependent adhesion pathways

Ly-6C belongs to the Ly-6 family of glycosyl phosphatidylinositol-anchored surface glycoproteins and is expressed on a subset of mature CD8(+) T cells. Ly-6C ligation can mediate T cell activation and causes interleukin 2 secretion in cytolytic T cell clones. We characterize herein a new mAb 1G7.G10 against Ly-6C that recognizes an epitope involved in lymphocyte adhesion and in lymphocyte homing. Pretreatment of lymph node lymphocytes and of purified CD8(+) T cells (but not of lymphocytes depleted of CD8(+) T cells) with 1G7.G10 reduced their in vitro binding to lymph node high endothelial venules by 28% and 34%, respectively. This effect was bypassed by cross-linking Ly-6C molecules with 1G7.G10 and a second-step antibody. The in vivo homing of (donor) CD8(+) T lymphocytes to lymph nodes was reduced by Ly-6C blocking with 1G7.G10 (whole antibody) or with its fragments [F(ab) or F(ab)(2)] by 20% or by 32% and 48%, respectively. Cross-linking of Ly-6C in vitro induced very late antigen-4 and lymphocyte function-associated antigen 1-mediated aggregation of CD8(+) T cells, suggesting that ligand binding to Ly-6C leads to activation of integrins. This activation may facilitate homing of Ly-6C(+) CD8(+) T cells in vivo.