PROBLEM TO BE SOLVED: To provide a composition derived from foods activating NK (natural killer) cells and enhancing immunity, and a food or drink and/or a drug for immunostimulation treating or preventing diseases free from fundamental remedies, for example, the prevention of infection such as that with influenza, the prevention or the development of cancer, and the like.SOLUTION: Acid polysaccharides such as a culture of lactobacillus, polysaccharides refined from the culture and polysaccharides obtained by chemically or enzymatically phosphorylating polysaccharides are provided. An NK cell activator using the phosphorylated polysaccharides as an active ingredient is excellent in safety and further has a high NK cell activating effect.【課題】ＮＫ細胞を活性化し、免疫力を高める食品由来の組成物、およびインフルエンザなどの感染予防、癌の予防、進行の防止など、根本治療法のない疾患の治療または予防する免疫賦活用飲食品及び／又は医薬品の提供。【解決手段】乳酸菌の培養物、該培養物から精製した多糖類、多糖類を化学的又は酵素的にリン酸化して得られた多糖類などの酸性多糖類、【効果】リン酸化多糖類を有効成分とするＮＫ細胞活性化剤は安全性に優れ、その上ＮＫ細胞活性化効果が高い。【選択図】なし
