The majority of research that has been done on turkey tail has been focused on polysaccharide krestin (PSK) and polysaccharide peptide (PSP). These are both compounds with patented extraction methods and are not necessarily found in high amounts innately in the mushrooms.

Gut Microbiome. Turkey tail has demonstrated prebiotic-like activity in vitro and in vivo. In vitro research has shown that the fermentation of PSP extract by gut bacteria increases the beneficial bacteria Bifidobacterium and Lactobacillus spp. while reducing the less desirable bacteria, Clostridium difficile, Staphylococcus spp. and Enterococcus spp. This study also saw increased levels of lactate and beneficial short chain fatty acids (1).

Immune. PSK extract modulates the immune response through stimulation of both extracellular pattern recognition receptors (TLR2) and intracellular pathogen sensors (NLRP3 inflammasome) (2). There have been many peer-reviewed publications on the immune benefits of turkey tail extracts, including 37 in vitro articles, 55 animal studies, 43 published human clinical studies, and 11 review articles in gastrointestinal, breast, and lung immune dysregulation. In the last two years, five more PSK trials in colorectal cancer have been published. Trametes water extract is made up of 62% polysaccharide and 38% PSK. After ingestion, PSK is highly bioavailable and can be found in the bone marrow, salivary glands, brain, liver, spleen, and pancreas in mice and rabbits within 24 hours. Once absorbed, PSK induces cytokine modulation, increasing TNF-α, IFN-γ, IL-2 and IL-8 (3).

​

It is important to note that PSK is a patented extract from a specific strain of Trametes versicolor and the PSK noted in these studies is not necessarily the same polysaccharide-protein that is found in the T. versicolor fruiting body. However, T. versicolor mushroom does contain other protein bound polysaccharides that likely have a similar function.