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-c production, indicating that Gl-PS can improve the nature of B16F10 cells to activate lymphocytes. Furthermore, H-2D b [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.The concept of immunosurveillance was first presented in 1957 and supported by the evidence of tumour-specific antigens [1]. However, the immune system in patients with cancer often fails to control tumour growth because of deficient immunogenicity of the tumour cells. Tumour cells use various strategies to evade the recognition by the host immune system. Mechanisms, such as MHC class I down-regulation, antigen loss, antigen modulation or the expression of inhibitory molecules, may explain the failure of an endogenous immune response in tumour control [2]. A major goal of immunotherapy is to generate an effective cell-mediated immune response with active or adoptive immunotherapy. It is clearly important to enhance immunogenicity of malignant tumour cells for induction of anti-tumour responses; however, attempts to activate a specific immune response against malignancies have been tried with only limited success.Ganoderma lucidum (Gl) has been widely used in China for centuries to promote longevity and improve vigour without appreciable adverse effects [3]. Ganoderma lucidum polysaccharides (Gl-PS), extracts from Gl, have multiple biological activities. Over the past two decades, numerous studies have demonstrated the immunomodulatory and antitumour activities of Gl-PS [4-6]. The anti-tumour effect of Gl-PS is believed to be mediated primarily by immune mechanisms. Gl-PS can increase cytokine production, improve dendritic cell maturation and function [7], improve cytokine-induced killer cell (CIK) function [5], improve cytotoxic T lymphocytes (CTL) function [8], and inhibit the growth of vascular endothelial cell and the induction of vascular endothelial growth factor (VEGF) in human lung cancer cell [9]. Gl-PS can also enhance the function of immunological effector cells in immunosuppressed mice [10]. In addition, recent research has shown that Gl-PS can reverse multidrug resistance (MDR) by down-regulating the expression of MDR-1 and MDR-assoc...