Abstract:  The immune system in patients with cancer often fails to control tumour growth because of deficient immunogenicity of tumour cells. Ganoderma lucidum polysaccharides (Gl-PS) are believed to have anti-tumour effects by boosting host immune function. Additionally, Gl-PS may have some direct effects on tumour cells in the activation of lymphocytes, thus enhancing the immunogenicity of tumour cells. We tested the effects of Gl-PS in lymphocyte activation by incubating Gl-PS with a tumour cell line deficient in antigen presentation. Our study showed that Gl-PS can promote B16F10 melanoma cells to induce lymphocyte proliferation, CD69 and FasL expression and IFN-γ production, indicating that Gl-PS can improve the nature of B16F10 cells to activate lymphocytes. Furthermore, H-2Db [a major histocompatibility (MHC) class I molecule], and B7-1 and B7-2 (two prominent co-stimulatory molecules expressed on B16F10 cells) were enhanced by Gl-PS, suggesting that these molecules may at least partially be involved in the process of Gl-PS on B16F10 cells to activate lymphocytes.