Antibody blockade of Thy-1 (CD90) impairsmouse cytotoxic T lymphocyte induction by anti-CD3 monoclonal antibody

Thy-1 (CD90)expressed by mouse T cells is known to have signal transducing properties,but the ability of Thy-1 to enhance cytotoxic T lymphocyte (CTL)development is not well understood. Here we show that stimulationof mouse T cells with monoclonal antibodies (mAb) to CD3, CD28 andThy-1 (clone G7), which were coimmobilized on polystyrene microbeads,resulted in a greater proliferative response than stimulation withonly anti-CD3 and anti-CD28 mAb, indicating that Thy-1 cross-linkingenhanced T cell receptor/CD28-driven T cell activation.Consistent with this finding, Thy-1 blockade with a soluble nonactivatinganti-Thy-1 mAb (clone 30-H12) inhibited anti-CD3-induced proliferationof CD4(+) and CD8(+) T cells,and the induction of cytotoxic effector cells in a dose-dependentfashion. Interleukin-2 synthesis and CD25 expression were also impairedby Thy-1 blockade. The inhibitory effect involved a defect at orbefore the level of protein kinase C activation because the additionof phorbol ester ablated the anti-Thy-1-mediated inhibition of anti-CD3-inducedT cell activation. The CTL that were induced in the presence ofblocking anti-Thy-1 mAb adhered to target cells but showed reducedexpression of granzyme B and perforin. In contrast, Fas ligand expressionand function was not affected by Thy-1 blockade. We conclude thatThy-1 signalling promotes the in vitro generation of CTLthat kill in a granule-dependent fashion.