FOLLOWING ANTIGEN CHALLENGE, T-CELLS UP-REGULATE CELL-SURFACE EXPRESSION OF CD4 IN-VITRO AND IN-VIVO

The low precursor frequency of Ag-specific T cells has raised signific ant barriers to studying the T cell response in vivo. We demonstrate t hat T cells up-regulate the cell surface expression of CD4 following A g recognition, which identifies Ag-specific T cells in vitro and in vi vo and allows their characterization. The CD4(high) cell subpopulation contains the Ag-specific population as indicated by Ag-induced prolif eration and limiting dilution analyses, The use of the CD4(high) marke r will allow analysis of the dynamics of the T cell immune response in vivo, the study of the suboptimal T cell response to Ag, and the iden tification of T cells which are reactive to known and unknown autoanti gens.