Enhancement of antitumor cytotoxicity of hepatic lymphocytes by oral administration of PSK.

We have studied the effects of oral administration of a biological response modifier (BRM), PSK, on hepatic lymphocytes. Many PSK positive cells were observed in the liver by anti-PSK antibody staining. Flow cytometric analysis revealed an increase in the number of OX8 (CD8) positive cells in the non-parenchymal nonadherent liver cells (NPNALCs) which were isolated from the liver enzymatically digested by perfusion with collagenase. NPNALCs were fractionated by discontinuous density gradient centrifugation, and the number and cytotoxic activity of these cells were examined in each fraction. Although the yield of lymphocytes in each fraction was not significantly increased by the oral administration of PSK, the natural killer (NK) activity was markedly enhanced in low density fractions. The present findings suggest that oral administration of PSK is effective for prevention of liver metastasis through the augmentation of organ-associated NK activity.