ABSTRACT
Interactions among immune cells and those of immune cells with other tissue cells are highly complex and not yet completely understood. They are essential to maintain health, and when disturbed, disease may follow. Immunomodulating agents that are free from side effects and can be administered for a long duration, if possible throughout life, for continuous immune activation are highly desirable for the prevention of diseases, both infectious diseases and diseases of the aged, such as cancer. Uses of plants or herbal products to improve defenses against various diseases have a long history. There has been remarkable interest in the past few decades in plants that are capable of modulating the immune system in favor of the host. As a result, several laboratories around the world tested plant extracts, newly identi‹ed and existing natural products, for their immunomodulatory effects in both in vitro and in vivo experimental models, and there were some clinical trials to test their ef‹cacy in humans. In the Indian system of medicine called Ayurveda, several plants or herbs, either alone or in combinations, have been used to treat a variety of human diseases. Experimental analysis of many of these herbs demonstrated potent immunomodulatory activity. Some of the well-known plants that are widely used in the clinics are Withania sominifera, Asparagus recemosus, Phyllanthus emblica, Tinospora cordifolia, Allium sativum, and others (Govindarajan et al., 2005).
