Antigen-specific CD4⁺ T-cell responses to cognate antigen presented by STI-571–treated APCs. PEMs (1 × 10⁵/well) or BM-derived DCs (1 × 10⁴/well) from BALB/c mice were cultured for 24 hours in media alone (No LPS), STI-571 (STI, 10 μM), LPS (5 μg/mL), or LPS plus STI-571 as indicated (1 or 10 μM). Then, supernatants were collected and 5 × 10⁴ purified naive T cells from the spleen of anti-HA TCR mice were added to the APCs in the presence or not of 12.5 μg HApeptide_110-120. After 48 hours, IL-2 and IFN-gamma production by antigen-specific T cells in response to HA-peptide presented by either PEMs (A,C) or BM-derived DCs (B,D) was determined by ELISA. Data represent mean ± SE of triplicate cultures and are expressed as the amount of cytokine produced per 100 clonotype⁺ T cells/well. Shown is a representative experiment of 4 independent experiments with similar results (*P statistically significant for the difference in cytokine production between treatment with LPS + STI-571 and LPS alone).