Cutting edge: In vivo identification of TCR redistribution and polarized IL-2 production by naive CD4 T cells

TCR aggregation at the point of contact with an APC is thought to play an i mportant role in T cell signal transduction. However, this potentially impo rtant phenomenon has never been documented during an immune response in viv o. Here we used immunohistology to show that the TCR on naive Ag-specific C D4 T cells in the lymph nodes of mice injected with Ag redistributed to one side of the cell. In cases where the APC could be identified, the TCR was concentrated on the side of the T cell facing the APC. In those T cells tha t produced IL-2, the TCR and IL-2 localized to the same side of the cell. I n vivo IL-2 production depended on costimulatory signaling through CD28, wh ereas TCR redistribution did not. These results show that Ag-stimulated CD4 T cells produce IL-2 in a polarized fashion and undergo CD28-independent T CR redistribution in vivo.