American BioSciences NK-9 Immune System Support for Dogs & Cats provides the immune support your pet needs to stay healthy and happy. Every pet’s immune system contains cells called Natural Killer (NK) cells, the most important white blood cells in their system. These cells are designed to defend against foreign or dangerous substances that invade the body. NK-9 contains Active Hexose Correlated Compound, a powerful ingredient proven to enhance Natural Killer cell activity, providing your best friend with the best protection.