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 unresponsivenessinduced by soluble anti-CD3 mAb in the presence of accessorycells, T cells purified from peripheral blood of healthy volunteerswere cultured for 4 days with irradiated accessory cells andOKT3. After a 48 h resting period allowing TCR—CD3 complexre-expression, T cells were rechallenged with plastlc-immobilizedOKT3, and their proliferative response as well as their secretionof IL-2, IFN-and IL-10 measured. Primary culture with OKT3 induceda state of unresponsiveness characterized by defective responsesto OKT3 rechallenge but normal or enhanced responses to PMAand A23187 calcium ionophore, indicating a defect in the earlysteps of TCR—CD3-mediated signal transduction. Indeed,we found that unresponsive T cells displayed an impaired mobilizationof intracellular calcium stores upon TCR—CD3 ligatlon.In order to determine whether the development of unresponsivenessdepends on the initial T cell activation triggered by OKT3,we compared several versions of OKT3 differing in their abilityto bind Fc receptors. We found that only the activating antibodiesthat bind Fc receptors on accessory cells induced T cell unresponsiveness.We conclude that human resting T cells can be rendered unresponsiveby anti-CD3 mAb in soluble form provided that they trigger Tcell activation.