Immunomodula Tion

The immunomodulatory effect of ginseng is based on the production of cytokines, activation of macrophages, stimulation of bone marrow cells and stimulation of iNOS, which produces high levels of NO in response to activating signals from Th1 -associated cytokines and plays an important role in cytotoxicity and cytostasis (growth inhibition) against many pathogenic microorganisms. In addition to its direct effector function, NO serves as a potent immunoregulatory factor.

Ginseng enhances IL-12 production and may therefore inducea stronger Th1 response, resulting in improved protection against infection from a variety of pathogens (Larsen et al 2004), including Pseudomonas aeruginosa lung infection in animal models (Song et al 2005), although other studies suggest that it may also assist in the correction of Th1 -dominant pathological disorders (Lee et al 2004a).

Ginseng polysaccharides have been shown to increase the cytotoxic activity of macrophages against melanoma cells, increase phagocytosis and to induce the levels of cytokines, including TNF-alpha, IL-1 -beta, IL-6 and IFN-gamma in vitro (Shin et al 2002). Ginseng has been shown to be an immunomodulator and to enhance anti-tumour activity of macrophages in vitro (Song et al 2002). Ginseng has also been shown significantly to enhance NK function in an antibody-dependent cellular cytotoxicity of peripheral blood mononuclear cells in vitro (See et al 1997).

Incubation of macrophages with increasing amounts of an aqueous extract of ginseng showed a dose-dependent stimulation of iNOS. Polysaccharides isolated from ginseng showed strong stimulation of iNOS, whereas a triterpene-enriched fraction from an aqueous extract did not show any stimulation. As NO plays an important role in immune function, ginseng could modulate several aspects of host defence mechanisms due to stimulation of the iNOS (FriedI et al 2001).

Ginseng promotes the production of granulocytes in the bone marrow (granulocytopoiesis). The ginseng saponins have been shown to directly and/or indirectly promote the stromal cells and lymphocytes to produce human granulocyte-macrophage colony-stimulating factor (GM-CSF) and other cytokines and induce © 2007 Elsevier Australia

bone marrow haemopoietic cells to express GM-CSF receptors, leading to a proliferation of human colony-forming units for granulocytes and macrophages in vitro (Wang et al 2003).

Ginseng polysaccharides have been shown to have potent antisepticaemic activity by stimulating macrophages and helping modulate the reaction against sepsis induced by Staphylococcus aureus. Ginseng polysaccharides have been shown to reduce the intracellular concentration of 5. aureus in macrophages in infected animals by 50% compared with controls. Combination of the ginseng polysaccharides with vancomycin resulted in 100% survival of the animals whereas only 67% or 50% of the animals survived, respectively, when treated with the ginseng polysaccharides or vancomycin alone (Lim et al 2002a).

According to animal studies long-term oral administration of ginseng extract may potentiate humoural immune response but suppress spleen cell functions (Liou et al 2005).

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