Oral administration of freshly expressed juice of Echinacea purpurea herbs fail to stimulate the nonspecific immune response in healthy young men: results of a double-blind, placebo-controlled crossover study.

Echinacea extracts are widely used in European countries and in the United States as "immune-stimulating" agents. Even though the evidence to stimulate certain components of the nonspecific immune system (phagocytosis, macrophages, and production of cytokines) stems from in vitro experiments or studies after parenteral application, the commercially available Echinacea preparations used as drugs or supplements are for oral use. The aim of the study was to determine whether phagocytic activity and production of cytokines is stimulated by oral application of a commercially available Echinacea preparation. Forty healthy male volunteers (ages 20-40 years) participated in the study. They received either a freshly expressed juice of Echinacea purpurea herbs or placebo juice using a double-blind placebo-controlled crossover design with two treatment periods of 14 days and a wash-out period of 4 weeks in between. Endpoints for immune stimulation: phagocytic activity of polymorphonuclear leukocytes and monocytes measured by flowcytometry, production of tumor necrosis factor alpha (TNF)-alpha and Interleukin (IL)-1beta by LPS-stimulated blood monocytes. Echinacea purpurea herbs did neither enhance phagocytic activity of polymorphonuclear leukocytes nor that of monocytes when compared with placebo. Echinacea purpurea herbs did not influence the production TNF-alpha and IL-1beta by LPS-stimulated monocytes. Unexpectedly, Echinacea purpurea herbs decreased serum ferritin concentration (p = 0.0005). All other laboratory and safety data remained unchanged. The "immune stimulation" by Echinacea purpurea observed in vitro and after parenteral administration are not confirmed in healthy humans after oral intake. Other immunomodulatory effects may explain the benefits of Echinacea preparations in reducing duration and severity of upper-respiratory tract infections found in randomized, double-blind clinical trials.