Abstract

This study investigates the immunomodulating effects of cucurbitacin B, a Thai herbal plant; isolated from Trichosanthes cucumerima L., on PHA-stimulated human Peripheral Blood Mononuclear Cells (PBMCs). Stimulated PBMCs were cultured in the presence or absence of cucurbitacin B and then markers of cell activation were measured. The results showed that 0.5 and 0.25 µg/ml of cucurbitacin B significantly inhibited the expression of CD69+CD3+, and CD25+CD3+ whereas no significant inhibition from 0.05 µg/ml of cucurbitacin B was detected. The secretion of TNF-a from stimulated PBMC was significantly inhibited by cucurbitacin B. After 24 h of incubation, the total Cytotoxic Lymphocyte (CTL) activity was significantly reduced by 0.5 µg/ml of cucurbitacin B when compared to the control group (9.83 ± 0.95 and 40.63 ± 2.93, P = 0.0033) or compared with Phytohemagglutinin (PHA) stimulation (9.83 ± 0.95 and 70.09 ± 3.35, P < 0.0001). A similar pattern of CTL activity was found after 48 and 72 h of incubation. In conclusion, cucurbitacin B inhibited PBMC activation by PHA. This study provides evidences that cucurbitacin B could be used as immunosuppressive agent.

Key words: Cucurbitacin B, Phytohemagglutinin stimulated peripheral blood mononuclear cell, cytotoxic lymphocyte function, CD69.