Early programming of T cell populations responding to bacterial infection

The duration of infection and the quantity of Ag presented in vivo are comm only assumed to influence, if not determine, the magnitude of T cell respon ses. Although the cessation of in vivo T cell expansion coincides with bact erial clearance in mice infected with Listeria monocytogenes, closer analys is suggests that control of T cell expansion and contraction is more comple x. In this report, we show that the magnitude and kinetics of Ag-specific T cell responses are determined during the first day of bacterial infection. Expansion of Ag-specific T lymphocyte populations and generation of T cell memory are independent of the duration and severity of in vivo bacterial i nfection. Our studies indicate that the Ag-specific T cell response to L. m onocytogenes is programmed before the peak of the innate inflammatory respo nse and in vivo bacterial replication.