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.