Lactic acid strongly diminishes cytokine production in CTLs. (A) CTLs were incubated for 16 hours with or without lactic acid, lactic acid/buffered with NaOH, or sodium lactate and then stimulated for another 5 hours with PMA/ionomycin in the presence of the substances. Cells were stained intracellularly with mAbs for IL-2 and IFN-γ and analyzed by flow cytometry. Results are representative of 3 independent experiments. (B) CTLs were cultured in the absence or presence of 5 to 20 mM lactic acid, sodium lactate, or HCl (∼ pH 6.8). Data represent means ± SEM; n = 4. (C) IL-2, IFN-γ, and CD8 mRNA were determined by quantitative RT-PCR after stimulation for 3 hours with PMA/ionomycin in the presence of 20 mM lactic acid, 20 mM sodium lactate, or HCl (∼ pH 6.8). Data are means ± SEM; n = 4. (D) CTLs were treated for 24 hours with 20 mM lactic acid (LA), washed, and recovered for 24 hours in normal medium (med). Intracellular cytokines were determined by flow cytometry. Results are representative of 3 independent experiments. **P < .0016; ***P < .0001.