Let's talk turkey. Strengthening the health of your immune system is a priority. That's where Organic Turkey Tail Mushroom powder from fruiting body comes in. Krestin (PSK) and Polysaccharide Peptide (PSP) are two types of polysaccharopeptides found in turkey tail mushrooms and are potent promoters of your immune response by both activating and inhibiting specific types of immune cells and by suppressing inflammation.