Panel A - LysiSpot assay. LysiSpot assay results, expressed as net number of spots per well (spots from wells containing only target cells were subtracted), from four different experiments (mean ± SD). Increasing numbers of target cells were plated in short term cultures with effector cells (2 × 105/well PBMC). Spots were the imprint of β-gal, released by the transfected DHD-K12 target cells after lysis. Cytotoxic activity of PBMC from DHD-K12-inoculated rats or control rats are represented by dark and light grey respectively. Panel B - LDH-Cytotoxicity assay. Cytotoxic activity expressed as percent of specific lysis (mean ± SD) of DHD-K12 target cells from PBMC of intact (control) or DHD-K12-inoculated rats (Primed) evaluated by Promega CytoTox 96 kit. Concentration ratio of effector and target cells was 10:1 (light grey), 5:1 (dark grey), 2.5:1 (white), 1.25:1 (black) and corresponding respectively to 2 × 104,1 × 104, 5 × 103, 2.5 × 103 of DHD-K12 target cells.