Protein-bound polysaccharide K

Protein-bound polysaccharide K was kindly provided by Kureha Chemical Industry (Tokyo, Japan). It is prepared by extracting cultured mycelia of C. versicolor with hot water. The precipitate is separated from the clear supernatant with saturated ammonium sulfate, then desalted and dried [25]. Protein-bound polysaccharide K was dissolved in RPMI medium or water and heated at 50°C for 20–30 min until a clear solution appeared. The PSK preparation was filter-sterilized and diluted in culture medium or water to the desired concentration. Protein-bound polysaccharide K was titrated previously in NKL cells [23] and the working dilution we used was 100 μg/ml.