In vitro immunomodulatory effects of ten commonly used herbs on murine lymphocytes

Objectives: Physicians are increasingly encountering patients who use herbal products. Some of these products are known to modulate the immune system but their scientific basic is not well established. Because these products can affect the host immune system, they could be beneficial in the treatment of immune-related diseases, or alternatively, they could cause inadvertent side-effects. The purpose of this study was to determine which of these common herbal products modulate lymphocyte proliferation in vitro. Methods: Lymphocyte proliferation assays using concanavalin A (mitogen stimulation) and mixed lymphocyte culture (alloantigen stimulation) were used as in vitro tests to investigate the immunomodulatory effects of 10 commonly used herbal products. Results: Ginger and tea were consistently immunosuppressive while dong quai, milk thistle, and St. John's wort were consistently immunostimulatory in vitro. Ginseng enhanced lymphocyte proliferation only in the mitogen-stimulation assay. The magnitude of the enhancement or suppression of the individual herbal products was different in the two assays. Conclusion: Our study provides a uniform survey of the immunomodulatory properties of 10 commonly used herbal products and paves the way for testing these effects in vivo and in clinical setting.