A fungal immunomodulatory protein (FIP-gts) was purified from Ganoderma tsugae. Recombinant FIP-gts was expressed as glutathione S-transferase fusion protein in E. coli. In this study, recombinant FIP-gts promoted cell cycle progression from G0/G1 to S phase and signaling pathways were investigated in human peripheral mononuclear cells (HPBMCs) by PI staining and flow cytometry. FIP-gts significantly induced cytokine interferon-gamma (IFN-gamma) expression. Pre-treatment of cells with phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294002 abolished FIP-gts, induced increase in S phase, and inhibited IFN-gamma secretion. Akt, a downstream effector of PI 3-kinase was phosphorylated and activated by FIP-gts. Results show that FIP-gts is a potent activator in PBMC and its effects are mediated via cytokine regulation of PI 3-kinase. (C) 2008 Elsevier Ltd. All rights reserved.