The (probable) active ingredients of the herbal compounds in Table 12.1 tend to fall into a limited number of chemical families; one of these is high-molecular-weight polysaccharides, which are large sugar molecules. Natural compounds containing them include Astragalus, Ganoderma, Eleutherococcus, and PSK. A second family of immunostimulating compounds is the saponins. Natural compounds with these are Eleuthero-coccus and ginseng. It is tempting to speculate that the most effective combinations of herbal immune stimulants will contain compounds from both families, and in fact, most multiherb, immunostimulating formulas used in Chinese herbal medicine do have both. Some herbs themselves also include compounds from both families, as is the case with Eleutherococcus and ginseng.
The mechanisms by which herbal compounds exert their immunostimulant effects are not well understood, but often they include the production of im-munostimulating cytokines or modulation of cytokine effects. For example, Astragalus polysac-charides have been reported to potentiate the in-vitro antitumor cytotoxicity of lymphokine-activated killer cells generated with low-dose IL-2. The exact mechanism was uncertain but could have been due to Astragalus-induced increases in IL-2 receptor expression on the LAK cells, or some other form of increased IL-2 binding.14 As another example, one study reported that Ganoderma polysaccharides increased production of cytokines by macrophages and T cells and increased the cytotoxic effect of macrophages against leukemia cells in vitro. The cytokines that were increased included IL-1, IL-6, TNF, and interferon-gamma.15 Lastly, these compounds may work synergistically with IL-2 itself or possibly other natural compounds that increase IL-2 production. For example, a synergistic antimetastatic effect was seen when IL-2 was combined with the mushroom polysac-charide lentinan in mice. Little effect on metastasis occurred with either agent alone, but an 85 percent reduction was observed when the compounds were com-
Regardless of their exact modes of action, the final result of these herbal compounds is stimulation of both the innate and adaptive immune responses. As would be expected, these compounds produce antitumor effects in rodents. In humans, PSK has been the most extensively studied, and results suggest it may be useful in preventing recurrence after surgical removal of some tumors (see Chapter 16).
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