In this video, pre-stimulated antigen presenting cells (APCs, namely dendritic cells and macrophages, obtained after isolation and in vitro differentiation of bone marrow cells from C57BL/6 mice, pre-stimulation of the APCs has been done with IFN-gamma and LPS) are cultured with freshly isolated “naïve T cells” from the spleen of OT-I mice and observed at a frequency of 1 image every 10 sec for 16 hours.*