The induction of human T cell unresponsiveness by soluble anti-CD3 mAb requires T cell activation.

In order to obtain an in vitro model of human T cell unresponsiveness induced by soluble anti-CD3 mAb in the presence of accessory cells, T cells purified from peripheral blood of healthy volunteers were cultured for 4 days with irradiated accessory cells and OKT3. After a 48 h resting period allowing TCR-CD3 complex re-expression, T cells were rechallenged with plastic-immobilized OKT3, and their proliferative response as well as their secretion of IL-2, IFN-gamma and IL-10 measured. Primary culture with OKT3 induced a state of unresponsiveness characterized by defective responses to OKT3 rechallenge but normal or enhanced responses to PMA and A23187 calcium ionophore, indicating a defect in the early steps of TCR-CD3-mediated signal transduction. Indeed, we found that unresponsive T cells displayed an impaired mobilization of intracellular calcium stores upon TCR-CD3 ligation. In order to determine whether the development of unresponsiveness depends on the initial T cell activation triggered by OKT3, we compared several versions of OKT3 differing in their ability to bind Fc receptors. We found that only the activating antibodies that bind Fc receptors on accessory cells induced T cell unresponsiveness. We conclude that human resting T cells can be rendered unresponsive by anti-CD3 mAb in soluble form provided that they trigger T cell activation.