PolyI:C treatment–induced proliferation of adoptively transferred spleen and BM CD8 cells in spleen, PLN, and BM of recipient mice. CD8-enriched cell preparations were obtained by negative magnetic selection from either spleen of CD45.1 B6 mice or BM of B6 mice. In some experiments, the reverse combination of spleen and BM donor mice was used and results were similar. In each experiment, CD8 cell enrichment was checked by flow cytometry and cell preparations from spleen (80%–90% CD8 cells) and BM (40%–50% CD8 cells) were mixed in a 1:1 CD8-cell ratio. After CFSE labeling, donor cells were injected intravenously in CD45.1 B6 mice. The next day, mice were either injected with 150 μg polyI:C or left untreated and CFSE-labeled CD8 cell proliferation was examined after 3 days. Spleen, PLN, and BM cells were stained with TCR Alexa 647, CD8 PerCP-Cy5.5, and CD45.1 PE. CFSE-labeled TCR⁺CD8⁺ cells were examined and the percentage of divided cells was determined either within CD45.1⁺ or CD45.1 ⁻ cells. For each experiment, the marker was set based on CFSE intensity of cells from an untreated mouse. (A) CFSE labeling profile. Representative CFSE profiles are shown for either CD45.1⁺ (spleen donor) or CD45.1 ⁻ (BM donor) cells, obtained from spleen, PLN and BM of a polyI:C-treated mouse. Control-cell profiles from an untreated mouse are shown with gray lines. The numbers represent the percentages of divided cells in the marked region. The scale on x-axis is logarithmic, in arbitrary units, and that on y-axis is linear (maximum value 50, except for recipient BM panels, which have maximum value 20). (B) Percentages of divided cells within CFSE-labeled cells. Average values are shown by the horizontal bar. The panels summarize the results obtained in 3 independent experiments.