Effects of Edible Algae on Immune Responses: Algae Polysaccharides Regulate Delayed-type Hypersensitivity and Tumor Growth

Algae are eaten as health food in many Asian countries. We summarize our recent results regarding the immunoregulatory role of polysaccharides from edible algae on delayed-type hypersensitivity (DTH) and antitumor immune responses using mice. These algae are divided into two types; those which manipulate immune responses through toll-like receptor 4 (TLR 4), and those which use different receptors to modify the immune response. Petalonia binghamiae polysaccharides attenuate DTH and tumor growth by reducing the production of inflammatory cytokine, IL-17 through TLR4. The serum level of IL-17 was decreased significantly, only when P. binghamiae polysaccharides were administered intraperitoneally in the DTH response. Intraperitoneal administration of other brown algae polysaccharides, such as alginic acid did not suppress the DTH response nor reduced the serum level of IL-17. Although orally administered P. binghamiae polysaccharides did not reduce the serum level of IL-17, they inhibited the migration of eosinophils. These results suggest that the inhibition of either the generation of IL-17 or the migration of eosinophils is effective in regulating inflammation, and that these two events were separately regulated. Here, we present data suggesting that either the peritoneal or oral administration of P. binghamiae polysaccharides efficiently inhibits the migration of eosinophils to the site of inflammation in a DTH model using IL-5 transgenic mice. Alginic acid suppressed tumor growth in both C3H/HeN and C3H/HeJ mice and did not suppress the DTH response as strongly as P. binghamiae polysaccharides. We propose the potential usefulness of edible algae as fine tuning reagents of the immune responses.