Immunoenhancing properties of Plantago major leaf extract

Plantago major (PM), also known as plantain, is a weed found in temperate zones worldwide. PM leaves have been associated with various biological properties ranging from antiinflammatory, antimicrobial and antitumour to wound healing. However, its mechanism of action associated with boosting of the immune function remains to be elucidated. We found that endotoxin‐free methanol extracts from PM leaves, at doses of 50, 100, 250, and 500 µg/mL, were associated with 4.4 ± 1, 6 ± 1, 12 ± 0.4, and 18 ± 0.4‐fold increases of nitric oxide (NO) production, and increased TNF‐α production (621 ± 31, 721 ± 36, 727 ± 36, and 1056 ± 52 U/mL, respectively) by rat peritoneal macrophages, in the absence of IFN‐γ or LPS. NO and TNF‐α production by untreated macrophages was negligible. In addition, PM extracts potentiated Con A‐induced lymphoproliferation (3‐ to 12‐fold increases) in a dose‐dependent fashion, compared with the effect of ConA alone. The regulation of immune parameters induced by plant extracts may be clinically relevant in numerous diseases including chronic viral infections, tuberculosis, AIDS and cancer. Copyright © 2000 John Wiley & Sons, Ltd.