Effects of PSK, an antitumor protein-bound polysaccharide, on the surface charge of lymphocytes in X5563-bearing mice.

Spleen and thymus cells from X5563 plasmacytoma-bearing mice treated with PSK (krestin) were analyzed by cell electrophoresis and flow microcytometry. A splenocyte electrophoretic pattern showed that an intermediate mobility peak (IMC), which appeared between the low (B cells) and high (T cells) peaks as the tumor developed, was depressed by the administration of PSK. Thy-1+ cells and asialo-GM1+ (aGM1+) cells decreased with tumor growth, and null cells without a marker of Ig, Thy-1 nor aGM1 increased. However, these changes were corrected by the administration of PSK. As the tumor grew, a thymocyte electrophoretic pattern showed that the incidence of low mobility cells, corresponding to immature cells, decreased, and that of high mobility cells, corresponding to mature cells in the medullary zone, increased. However, PSK suppressed the changes. The tumor did not disappear but life span was prolonged (121%) by the administration of PSK. These results lead to the conclusion that the administration of PSK prevented the changes in surface charge and markers of lymphocytes due to tumor burden, and restored the immunological responsiveness even in the syngeneic system.