The Science Behind It

PSK, PSP, and the Immune Receptor Science

• PSK (Polysaccharide-K) - Japan's Approved Cancer Adjuvant

  PSK, known commercially as Krestin, is a protein-bound beta-glucan polysaccharide isolated from Trametes versicolor. It has been an approved pharmaceutical adjuvant in Japan since 1977, used alongside conventional cancer treatment for gastric, colorectal, oesophageal, breast, and lung cancers. Multiple randomised controlled trials in Japan demonstrated that PSK alongside chemotherapy improved five-year survival rates versus chemotherapy alone across several cancer types. Its mechanism involves activating dendritic cell maturation, enhancing T-helper cell differentiation toward Th1 phenotype (which promotes cytotoxic immune responses against abnormal cells), and directly stimulating natural killer cell cytotoxicity. PSK also has anti-tumour properties through inhibition of cell migration and invasion pathways independent of immune activation. In the context of cancer supportive care, PSK is one of the most extensively validated natural immunomodulatory compounds in clinical medicine.
• PSP (Polysaccharide-Peptide) - Immune Restoration and Microbiome Balance

  PSP is a related protein-bound polysaccharide with a distinct protein moiety from PSK, identified through research in Chinese Turkey Tail strains. PSP has demonstrated immunomodulatory activity through different receptor pathways, providing complementary immune support to PSK's activity. A key study from the University of California Davis, investigating PSP's effects on the canine gut microbiome, found significant increases in Lactobacillus and Bifidobacterium populations and a reduction in Clostridium and Bacteroides species associated with gut dysbiosis. This microbiome shift was associated with improved stool quality and immune markers in the supplemented dogs, validating Turkey Tail's prebiotic gut-immune axis mechanism with canine-specific data.
• Beta-Glucan Receptor Binding - TLR2, TLR4 and Dectin-1

  Turkey Tail's beta-1,3/1,6-glucans are recognised by pattern recognition receptors on innate immune cells: Toll-like receptors TLR2 and TLR4, and Dectin-1 (also called CLEC7A). Binding to these receptors triggers a coordinated innate immune response including macrophage activation and cytokine secretion (IL-1, IL-6, TNF-alpha in appropriate contexts), dendritic cell maturation and antigen presentation, and natural killer cell cytotoxic priming. This is genuine immune modulation rather than non-specific stimulation - the beta-glucan signal primes immune cells to respond more effectively to actual threats without inducing the chronic inflammatory state that harmful immune overactivation produces. For dogs with seasonal allergies or autoimmune tendencies, this calibrated activation - enhancing specific surveillance while maintaining regulatory balance - is more appropriate than broad immune stimulants.
• The Hemangiosarcoma Veterinary Study

  The most cited veterinary study on Turkey Tail was conducted by researchers at the University of Pennsylvania School of Veterinary Medicine and published in Evidence-Based Complementary and Alternative Medicine. The study evaluated Turkey Tail polysaccharide extract in dogs with naturally occurring splenic hemangiosarcoma - an aggressive vascular cancer with poor prognosis in dogs. Dogs receiving the highest dose of Turkey Tail extract (100mg/kg) showed a median survival time of 117 days following splenectomy, compared to a historical control median of approximately 30 to 60 days for dogs receiving surgery alone. The researchers attributed this to Turkey Tail's immunostimulatory effects on NK cells and macrophages, which may delay tumour recurrence and metastasis. This is a small study and results were variable, but it represents the most substantive canine-specific clinical evidence for medicinal mushroom use in oncology supportive care currently available. Turkey Tail is supportive care - it does not cure hemangiosarcoma and should be used alongside, not instead of, veterinary treatment.