 Welcome to the Voice of America's Newswords. A kind of evergreen tree in Chile is increasingly important for producing new vaccines. Immune System The Kile tree has a kind of molecule that helps the body's immune system. Vaccine makers need only a tiny amount of the substance to produce a single treatment. But the tree's rarity has them worried about future supplies. The immune system is the body's natural defense system against infections and diseases. It includes white blood cells and antibodies designed to fight foreign substances in the body.