NK-9™ Immune System Support for pets helps provide unsurpassed support for a pet's immune system, especially their NK cells - a type of white blood cell known as the immune system's front-line defense. NK-9 contains AHCC (Active Hexose Correlated Compound), which is backed by more than 20 published studies and clinical experience with both humans and K9s. NK-9 is "the" AHCC product specifically formulated for pets.