Ly6C induces clustering of LFA-1 (CD11a/CD18) and is involved in subtype-specific adhesion of CD8 T cells

Ly6C is a hemopoietic cell differentiation Ag found on a subset of CD8 T cells in the periphery. It is involved in target cell killing by CTLs, augments TCR-mediated activation of IL-2 and IFN-gamma production in CD8 T cells, and regulates CD8 T cell homing in vivo. In this study, we show that cross-linking of Ly6C causes clustering of LFA-1 (CD11a/CD18) on the surface of CD8 T cells via a mechanism dependent on reorganization of actin cytoskeleton and intracellular protease, calpain, but not the phosphatidylinositol 3-kinase pathway. In the capillary flow-adhesion assay, Ly6C cross-linking significantly augments lymphocyte adhesion to endothelium, and this is inhibited by an Ab that blocks LFA-1 function. Furthermore, upon in vitro cross-linking and during in vivo homing into lymph nodes, Ly6C is transiently lost from cell surface but becomes re-expressed on lymph node-resident CD8 T cells. The abilities of Ly6C to induce LFA-1 clustering and to be re-expressed after signaling-associated down-regulation may be important in regulating the homing of CD8 T cells into lymph nodes and in subsequent steps of CD8 T cell activation and effector function that again involve LFA-1.