T cell avidity determines the level of CTL activation

To investigate the influence of avidity on T cell activation in vitro and in vivo, we analyzed T cells from St40 and St42 mice, which express the same transgenic TCR specific for an E1a-derived epitope of adenovirus type 5 with different expression levels and therefore different avidities. Splenocytes from both strains showed comparable cytolytic activities and required identical peptide concentrations for efficient target cell lysis and up-regulation of activation markers. However, the kinetics of CD25 up-regulation were strikingly different: whereas the majority of the high-avidity St42 T cells up-regulated the IL-2Ralpha chain within a few hours, low-avidity St40 T cells expressed only 5…