Religation of the T cell receptor after primary activation of mature T cells inhibits proliferation and induces apoptotic cell death

The proliferative response of murine splenic T cells, initially activated by cross-linking the TCR complex with either antibodies, mitogenic lectin, or alloantigen was severely inhibited when the activated cells were recovered and given an additional activation signal by recross-linking the TCR complex, or by adding Ca²⁺ ionophore and phorbol ester. Under the same conditions, cross-linking other T cell surface determinants such as CD4, CD8, or class I MHC on preactivated T cells had no effect. Assessment of cell viability using vital dye exclusion together with the detection of DNA fragmentation revealed that the reduction of the proliferative response was associated with an induction of apoptotic-like cell death in the activated T cell population and not due to a blockade of cell division. Accumulation of eosin stained (dead) cells did not occur immediately upon replating the activated cells, but began after a lag period during which at least two cell divisions occurred. In addition, perturbation of T cell proliferation after activation depended on how the cells were initially activated. Only T cells activated in the presence of additional cells found in spleen and lymph node were susceptible to inhibition; T cells activated after nylon wool purification were not susceptible. These results have potential implications for understanding self-tolerance and immunoregulation.