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BACKGROUND: Pseudomonas aeruginosa mannose-sensitive hemagglutinin (PA-MSHA) parenteral injection is used as a broad-spectrum immunomodulator. It remains unclear whether PA-MSHA exhibits inhibitory effects on tumor cell growth. OBJECTIVE: To investigate inhibitory mechanisms of PA-MSHA-induced proliferation in rat C6 glioma cells in vitro. DESIGN, TIME AND SETTING: Comparative observation and in vitro experiments were performed at the Key Laboratory of Natural Medicine, Kunming Medical College, China from July 2008 to April 2009. MATERIALS: Rat C6 glioma cell line (Shanghai Institute of Cell Biology, Chinese Academy of Sciences, China) and PA-MSHA parenteral injection (Beijing Wanteer Bio-Pharmaceutical, China) were used in the present study. METHODS: Rat C6 glioma cells in logarithmic growth phase were harvested in vitro. Adherent monolayer cells were respectively treated with PA-MSHA at final colony-forming units (cfu) of 1 × 108 cfu/mL, 2 × 108 cfu/mL, 4 × 108 cfu/mL, 6 × 108 cfu/mL, and 8 × 108 cfu/mL following 24 hours of conventional culture. MAIN OUTCOME MEASURES: MTT colorimetric assay was utilized to determine the inhibitory rate of C6 glioma cells following treatment with various concentrations of PA-MSHA at different times. Cell apoptosis was detected by fluorescent microscopy following Hoechst 33258 staining. Flow cytometry was used to measure PA-MSHA effects on C6 cell cycle. RESULTS: Inhibitory rate of C6 glioma cells increased with prolonged time and increased dose. Hoechst 33258 staining revealed obvious morphological changes in apoptotic C6 glioma cells. Flow cytometry revealed hypodiploid peaks, i.e., apoptotic peak, and the apoptotic rate in cells during S-phase significantly increased with increased concentrations in the experimental groups. CONCLUSION: With in vitro experiments, PA-MSHA preparations inhibited C6 glioma cell proliferation in a time- and dose-dependent manner. These mechanisms are likely associated with cell apoptosis induction and inhibition of the S phase.