Enhancement of T-cell proliferation by PSK

Abstract 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 Thyl 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 Thyl.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.