Natural killer cells are part of the body's innate, or first-line, immune response. They respond more quickly than the adaptive immune system comprised of B cells and T cells. Once activated, natural killer cell activity peaks in as quickly as several hours, providing rapid support and wide-range immune defense. EpiCor is a fermentate of Saccharomyces cerevisiae containing various bioactive metabolites. These nutrient metabolites are produced in a specialized fermentation process and enhance immune cell production. In one cellular study, EpiCor promoted natural killer cell activation, as well as that of B cells and T cells. In two randomized, double-blind, placebo-controlled trials, EpiCor provided statistically significant support for upper respiratory tract health and overall immune health. A separate open label, in-house trial indicated a strong potential for EpiCor supplementation to enhance secretory IgA levels after 30 days. These various actions demonstrate the ability of EpiCor to address both innate and adaptive immune responses. NAC (n-acetyl-l-cysteine) promotes endogenous glutathione production for antioxidant protection and provides lung defense mechanisms for healthy respiratory function. In a randomized, double-blind trial involving mostly older individuals, NAC showed support for respiratory health. Quercetin and elderberry provide flavonoids that offer additional support for immune and respiratory function while vitamin C, vitamin D and zinc play important roles in immune cell activation.