Immunostimulatory effects of a polysaccharide-rich substance with antitumor activity isolated from black currant (Ribes nigrum L.)

The fruit juice of black currant was found to contain a polysaccharide-rich substance, which was designated cassis polysaccharide (CAPS), with macrophage-stimulating activity. Especially, its interleukin (IL)-1beta-inducing activity was remarkably high, compared with other fruit juice preparations. CAPS was found to consist of rhamnose, mannose, arabinose, galactose, xylose, and glucose in a molar ratio of 11.3:0.9:54.1:29.8:2.0:1.9. CAPS turned out to be partitioned into a soluble component (CAPS-l.m.) and a precipitable component (CAPS-h.m.) with mean MWs of 80,000 and 600,000 respectively in 45% (v/v) ethanol solution. At least in vitro, CAPS-l.m. rather than CAPS-h.m. appeared to play an important role in macrophage activation. Oral administration of black currant juice and CAPS to Ehrlich carcinoma-bearing mice retarded the growth of the solid tumor by 45% and 51% respectively. CAPS administration had a stimulatory effect on the release of IL-2, IL-10, interferon-gamma, and IL-4 from splenocytes in comparison with PBS treatment in tumor-bearing mice. The IL-4 level was, however, still lower than that exhibited by a group of normal mice. CAPS showed a certain cytotoxicity directly against tumor cells.