Antigens are foreign substances that stimulate an immune response. While immune responses to protein antigens have been extensively studied, little is known about the way carbohydrate antigens stimulate the immune system. Carbohydrates in the outer layer of bacteria, called capsular polysaccharides (CPS), protect bacteria. Most bacteria that cause serious infections in humans have this characteristic. Dr. Motoi Maeda hopes to induce an immune response to CPS to prevent many diseases caused by bacterial infection. He has found that the CPS in two common strains of bacteria stimulates white blood cells called natural killer T cells (NKT). Motoi believes NKT cells are critical for initiating an immune response to disease-causing bacteria that have capsules for protection, and is researching how they are stimulated. This information could be used to create new vaccines against common infectious bacteria.