STUDIES ON IMMUNOREGULATORY MECHANISM OF FOOD COMPONENTS

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We examined the effect of irradiation on immunoglobulin (Ig) production of lymphocytes and found that it strongly suppressed their Ig production. The suppressive effect was enhanced in the presence of Rose Bengal, but depressed in the presence of α-tocopherol. In addition, we found that dietary tocotrienols had serum lipid-decreasing and Ig production-enhancing activities stronger than α-tocopherol. We also examined the dietary effect of γ-linolenic acid and found that it did not enhance of 4-series leukotriene production even at high dose administrations. On the contrary, it induced accumulation of dihomo-γ-linolenic acid in immune tissues, but the level was not correlated with their prostaglandin E_1 productivity. On immunoregulatory activity of dietary fibers, we examined the effect of aging. In aged rats, the expression of serum lipid-decreasing and Ig production-enhancing activities of water-soluble dietary fibers were weaker than those observed in young rats. Enhancement of Ig productivity in mesenteric lymph node lymphocytes was observed in aged rats as well as young rats, but not in splenocytes. This suggests that the target tissue of water-soluble dietary fibers is gut immune system in aged rats. In addition, we examined the combinational effect of dietary proteins and fats, and found that soy protein exerted stronger LTB_4 production-inhibiting activity than casein without affecting the level of arachidonic acid in immune cells. These results suggest that various food components exert regulatory activities on lipid metabolism and immune functions, and interact each other on the expression of their biological effect.