Lactic acid affects the cytotoxic activity and the availability of intracellular perforin and granzyme-B. (A) The cytotoxic activity of Melan-A–specific CTLs was determined by incubating CTLs with PKH26⁺ Melan-A peptide–loaded T2 target cells at indicated effector-target ratios. The cytotoxicity assay was performed for 3 hours in the presence of 15 mM lactic acid, 15 mM sodium lactate, HCL, or in normal medium. (B) Untreated CTLs (gray) or CTLs that were treated for 24 hours with 20 mM lactic acid (solid line) were analyzed for their intracellular content of human perforin and granzyme-B. Appropriate isotype control of untreated CTLs is shown (dashed line). Results are representative of 3 independent experiments. Mean of triplicate ± SEM. *P < .05.