The immunostimulant activity of echinacea has been the subject of countless studies. Overall, the fresh-pressed leaf juice of E. purpurea and alcoholic extracts of the roots of E. pallida, E. angustlfolla and E. purpurea have been shown to act mainly on nonspecific cellular immunity (Blumenthal et al 2000). Macrophage activation has been well demonstrated, as has stimulation of phagocytosis (Barrett 2003, Bauer et al 1988). Orally administered root extracts of echinacea have produced stronger effects on phagocytosis than aerial parts, with E. purpurea roots producing the greatest effect, followed by that of E. angustlfolla and E. pallida (Pizzorno & Murray 2006).
Activation of polymorphonuclear leukocytes and NK cells has been reported and increased numbers of T-cell and B-cell leukocytes. Research in human subjects has produced conflicting results, with some studies showing that echinacea stimulates non-specific immunity and others showing no significant effect (Roesler et al 1991, Schwarz et al 2002).
It is currently believed that no one single constituent is responsible for the herb's immunomodulating action, with the most important elements being polysaccharides, glycoproteins, alkamides and flavonoids (Ernst 2002).
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