Doctor's Best Immune Support Postbiotic features high-metabolite immunogens for healthy immune function support. While your immune system needs to be in top shape year-round for optimum health and vitality, many people make use of Immune Support Postbiotic specifically for seasonal wellness. Immune Support Postbiotic is a natural immune-supportive compound that fits into the unique category of being a high metabolite immunogen. It is a nutritive dried yeast fermentate that supports cellular metabolism and modulates immune function.