2006 年 39 巻 3 号 p. 162-167
In a previous study, COLD-fX (CVT-E002), a proprietary extract of the root of North American ginseng (Panax quinuefolium), was found effective in the prevention of upper respiratory tract infections (URIs) in healthy adults. The underlying mechanisms of its action, however, were not determined. The present study was carried out to explore if the effects observed could be due to COLD-fX-mediated changes in the distribution of peripheral blood leukocytes, changes in the relative distribution of lymphocyte subsets or IgA levels in plasma. At the onset of an influenza season, a total of 323 subjects between 18 and 65 years with a history of more than 2 colds in the previous year, participated in a randomized double-blind placebo-controlled study. The participants were instructed to take 2 capsules/day of either COLD-fX or placebo for a period of 4 months. Two blood samples were collected from 42 (COLD-fX = 21; placebo = 21) of the 323 recruited volunteers. These samples were obtained before and after the treatment, and were used for determination of white blood cell differential counts, enumeration of lymphocyte subsets and measurement of plasma levels of immunoglobulin A (IgA). The distribution of colds over the 4 month period was found to be similar in both treatment and placebo groups. However although non-significant, the severity of the colds in the COLD-fX group was found to decrease over time. COLD-fX intervention increased the proportion of T-helper and natural killer (NK) cells, and decreased IgA levels in plasma to a greater extent than the placebo. It is possible, therefore, that these cells acted synergistically to reduce the severity and duration of URIs in the COLD-fX group. Further studies are warranted to determine the effects of daily supplementation of COLD-fX on the activities of T-helper and NK cells in plasma.