Seselin from Plumbago zeylanica inhibits phytohemagglutinin (PHA)-stimulated cell proliferation in human peripheral blood mononuclear cells

Effects of seselin (C14H12O3; MW 228) identified from Plumbago zeylanica on phytohemagglutinin (PHA)-stimulated cell proliferation were studied in human peripheral blood mononuclear cells (PBMC). The data demonstrated that seselin inhibited PBMC proliferation-activated with PHA with an IC50 of 53.87 ± 0.74 μM. Cell viability test indicated that inhibitory effects of seselin on PBMC proliferation were not through direct cytotoxicity. The action mechanisms of seselin may involve the regulation of cell cycle progression, interleukin-2 (IL-2) and interferon-γ (IFN-γ) production in PBMC. Since cell cycle analysis indicated that seselin arrested the cell cycle progression of activated PBMC from the G1 transition to the S phase. Seselin suppressed IL-2 and IFN-γ production in a concentration-dependent manner. Furthermore, seselin significantly decreased the IL-2 and IFN-γ gene expression in PHA-activated PBMC. Therefore, results elucidated for the first time that seselin is likely an immunomodulatory agent for PBMC.