Injected DCs, and not endogenous DCs, are responsible for the cross-priming of OVA from live cells. Lethally irradiated C57Bl/6 rag2-deficient mice were reconstituted with K^bm1 (K^bm1⇒ B6) or CD45.1 (B6⇒ B6) bone marrow cells. (A) Spleen CD11c⁺ DCs from chimeras were sorted immunomagnetically and cultured overnight with OVA and LPS. Then they were cultured for 3 days with naive CFSE-stained OT-I T cells. At the end of the culture, cells were labeled and gated for CD8 and Vα2 expression to measure proliferation. (B-C) Chimeras were injected with naive CFSE-stained OT-I T cells. They were immunized one day later with DCs cultured with live L or L OVA cells, or with OVA_257-264 peptide, in the presence of LPS. Splenocytes were restimulated 3 days later with 3 μg/mL OVA_257-264 peptide for 4 hours and were labeled for CD8, Vβ5, Vα2, CD4, and IFN-γ. Proliferation (B) and IFN-γ production (C) were measured by flow cytometry. Data are mean ± SEM of 3 independent experiments performed in duplicate (B-C) or triplicate (A).