Norifumi Sugita

Direct action of a protein-bound polysaccharide, PSK, on transforming growth factor-β

We investigated the action of a protein-bound polysaccharide, PSK, on transforming growth factor-beta (TGF-beta). (1) In in vitro-mixed culture of peripheral blood mononuclear cells (PBMC) from healthy human and mitomycin C-treated human colon cancer cells, PSK or polyclonal antibody to TGF-beta significantly enhanced incorporation of 3H-thymidine into PBMC, and apparently decreased TGF-beta1 levels of acid-treated culture supernatant. (2) PSK or the antibody interfered with the quantitation by enzyme immunoassay of TGF-beta1 in acid-treated supernatant of the mixed culture. (3) PSK was suggested to form a complex with 125I-human recombinant TGF-beta1 standard, when changes in molecular weight of radioactivities were assessed by gel filtration. Recombinant human TGF-beta1 inhibited growth of mink lung epithelial cell line Mv1Lu and promoted collagen synthesis in rat kidney fibroblast cell line NRK49F, but the complex did not have such activities. (4) In addition to TGF-beta1, PSK bound with TGF-beta2 and platelet-derived growth factor; however, PSK did not bind with 22 other species of cytokines and growth factors. (5) Protein moiety of PSK is suggested to play an important role in the expression of the activity. These results suggest that PSK modulates the biological activity of TGF-beta1 by binding to its active form.

Enhancement of T-cell proliferation by PSK

Protein-bound polysaccharide, PSK, is a biological response modifier and influences various immunological functions in vivo, including those of T-cells. However, PSK has not been proved to stimulate proliferation of T-cells in vitro in contrast to various lines of evidence that indicate the proliferation of B-cells in vitro. PSK enhanced the proliferation of spleen cells in C3H/He and nude mice in vitro. In this study such proliferating cells were detected by monoclonal antibody to bromodeoxyuridine (BrdU) incorporated into DNA, and their subsets were determined by flowcytometry with monoclonal antibody to Thy1 as a cell surface marker of T-cells. When spleen cells from C3H/He mice were cultured with PSK for 3 days, the percentage of BrdU positive cells increased, and about 67% of BrdU positive cells were Thy1.2 positive. In addition, PSK also had the activity to enhance the proliferation in a T-cell-enriched fraction from spleen cells by nylon fiber columns as well as that in original spleen cells. These results suggest that PSK enhances the proliferation of T-cells as well as B-cells.

Antitumor Effect of a Biological Response Modifier, PSK, on C57BL/6 Mice with Syngeneic Melanoma B16 and Its Mode of Action

The effects of PSK, a protein-bound polysaccharide, on the survival period and effector cell activity were examined using C57BL/6 mice with melanoma B16. PSK prolonged the survival period of the mice with tumors in a schedule- and dose-dependent manner. However, no life-prolonging effect was observed when carrageenan-treated mice or congenitally athymic mice were used as hosts. PSK enhanced the cytostatic activity and interleukin-1-producing capacity of peritoneal exudate plastic-adherent cells in C57BL/6 mice with tumors. These findings suggested that PSK prolongs the survival period of mice with B16 tumors through T-cell- and macrophage-dependent mechanisms.

Treatment with Krestin combined with mitomycin C, and effect on immune response.

The combination effects of Krestin (PSK) and mitomycin C (MMC) were examined in experimental tumor models. PSK was administered either orally or intraperitoneally. Delayed-type footpad reaction and antibody formation against sheep erythrocytes were measured in hosts of which immune functions were depressed by tumor burden. Results of the experiment indicated that the simultaneous administration of PSK and MMC significantly increased the survival rate of tumor-bearing mice and restored more effectively their immune functions compared to those of nontreated tumor-bearing controls or tumor-bearing hosts treated with a single agent.