AIM: Valproic acid (VPA) is a histone deacetylase inhibitor and is believed to have anti-tumor activity. The present study aims to investigate the effect of VPA on the, apoptosis and cytokine synthesis of human peripheral lymphocytes. METHODS: The activation and cytokine synthesis in lymphocytes in whole blood stimulated with phorbol dibutyrate (PDB) and ionomycin were evaluated with flow cytometry after fluorescent staining. The mitochondrial membrane potential was examined using 3, 3-dihexyloxacarbocyanine iodide [DiOC6(3)]staining. RESULTS: VPA at low doses (1 and 5 mmol/L) promoted CD69 expression in activated lymphocytes, whereas it turned to inhibit the expression of CD69 at a high dose (25 mmol/L). Meanwhile, VPA at low doses increased the mitochondrial membrane potential, while a high dose of VPA decreased it in activated lymphocytes. Furthermore, interleukin-2 (IL-2) synthesis was enhanced by low doses of VPA but inhibited by a high dose. However, interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) synthesis were dose-dependently enhanced by VPA as compared with those of PDB plus ionomycin-treated cells. CONCLUSION: VPA exerts biphasic effect on the further activation and apoptosis of human peripheral lymphocytes stimulated with mitogens and exhibits differential activity on the synthesis of several important cytokines in human lymphocytes.

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