Natural killer cells from aging mice treated with extracts from Echinacea purpurea are quantitatively and functionally rejuvenated.
A growing body of anecdotal evidence in young and adult humans suggests that certain phytochemicals have the capacity to ameliorate tumors and reduce infections, especially those mediated by virus, in vivo. These indications prompted us, therefore, to investigate the potentially immuno-stimulating effect of one such phytocompound, Echinacea purpurea, on natural killer (NK) cells since these cells are active in spontaneous, non-specific immunity against neoplasms and virus-mediated infections. We elected to study aging mice, since, at this stage of life, like humans, the above-mentioned afflictions increase in frequency. We had previously found that neither the cytokine, interleukin-2, nor the pharmacological agent, indomethacin, both potent stimulators of NK cell numbers/function in younger adult mice, was effective in stimulating NK cells in elderly mice. The present study was designed to assess the numbers/production of NK cells in the spleen and bone marrow of aging, normal mice, after in vivo dietary administration of E. purpurea (14 days), or, after injection of thyroxin, a stimulant of NK cell function (10 days). Immunoperoxidase labeling techniques, coupled with hematologic tetrachrome staining were used to identify NK cells in both the spleen (primary site of NK cell function) and the bone marrow (site of NK cell generation). Double immunofluorscence staining, employing propidium iodide, was used to assess NK cell lytic function. Our results revealed that E. purpurea, but not thyroxin, had the capacity to increase NK cell numbers, in aging mice, reflecting increased new NK cell production in their bone marrow generation site, leading to an increase in the absolute numbers of NK cells in the spleen, their primary destiny. The E. purpurea-mediated increase in NK cell numbers was indeed paralleled by an increase in their anti-tumor, lytic functional capacity. Collectively, the data indicate that E. purpurea, at least, and possibly other plant compounds, appear to contain phytochemicals capable of stimulating de novo production of NK cells, as well as augmenting their cytolytic function, in animals of advanced age.