Background: Immune system is the most important system of human body. Thai folk doctors have used some medicinal plants as an adaptogenic drug or immunomodulatory agent. Piper chaba Hunter, Piper sarmentosum Roxb. and Piper interruptum Opiz. are used by folk doctors to activate immune response in cancer patients.
Objective: To investigate the effect on natural killer cell activity and on lymphocyte proliferation activity of water extract of P. chaba Hunter, P. sarmentosum Roxb. and P. interruptum Opiz.
Material and Method: Plant materials were extracted by decoction method. All extracts were tested for an immunomodulatory effect using PBMCs from twelve healthy donors by chromium release assay. Lymphocyte proliferation was also determined by 3H-thymidine uptake assay. The degree of activation was expressed as the stimulation index.
Results: The water extract of P. chaba Hunter significantly increased lymphocyte proliferation at concentrations of 1 ng/ml, 10 ng/ml, 1 μg/ml, 5 μg/ml, 10 μg/ml and 100 μg/ml. P. sarmentosum Roxb., and P. interruptum Opiz. extracts at those concentrations significantly stimulated lymphocyte proliferation. P. sarmentosum Roxb. extract significantly increased natural killer (NK) cell activity at a concentration of 100 μg/ml but P. chaba Hunter and P. interruptum Opiz. extracts did not significantly stimulate natural killer cell activity.
Conclusion: P. chaba Hunter, P. interruptum Opiz. and P. sarmentosum Roxb. have an immunomodulatory effect especially for P. sarmentosum Roxb. extract which can activate both lymphocyte proliferation and NK cell activity.

Keywords: Piper chaba Hunter, Piper interruptum Opiz., Piper sarmentosum Roxb., Immunomodulatory effect, NK cell, Lymphocyte proliferation