This mushroom originating from China is the most well-studied medicinal mushroom in the world and it is one of the very best mushrooms for assisting the immune system. Coriolus V. contains polysaccharide peptide (PSP) and polysaccharide-K (PSK, krestin), both of which have immune stimulating properties. Coriolus V. improves natural killer cell numbers in those feeling regular fatigue. It can raise the levels of T cells and therefore can help improving the immune responses, which may assist in clearing up infections. It also seems to increase the levels of T helper cells that help maintain and regulate immune responses and modulate antigen production.