ated with altered levels of MDSCs in eight breast cancer patients, we hypothesize that chronic psychological stress leads to elevated levels of MDSCs. In the present study, we investigated the relationship between psychological stress and MDSCs, and found that chronic psychological stress leads to the accumulation of PMNMDSCs in the bone marrow of BALB/c mice. 3: Chronic psychological stress Each mouse subjected to restraint was placed in a wellventilated 50-ml conical tube containing approximately one hundred 0.4-cm diameter holes. They were restrained for 5 consecutive nights during their active period each day. The restraint tubes were cleaned and sterilized between each restraint cycles. Since mice in the tubes did not have access to food and water during this time period, similarly food- and water-deprived, but not restrained, mice were used as control animals. To explore the effects of glucocorticoids, mice were MedChemExpress Salvianic acid A intraperitoneally injected with 25mg/kg RU486 and 10mg/kg antalarmin, or same volume of propylene glycol/ ethanol for five days. RU486 and antalarmin were dissolved in propylene glycol/ethanol. To explore the effects of catecholamines, mice were injected i.p with 2mg/kg epinephrine, 50mg/kg isoproterenol, 10mg/kg propranolol, or same volume of 0.9% saline for five days. Epinephrine, isoproterenol, and propranolol were dissolved in 0.9% saline. To explore the effects of COX-2, mice were injected with 10mg/kg SC-236 or same volume of dimethyl sulfoxide. SC-236 was dissolved in DMSO. Mice injected with epinephrine or isoproterenol did not undergo restraint stress. Mice injected with RU486 and antalarmin, propranolol, or SC-236 underwent restraint stress 1 hour after the injection. Materials and Methods 1: Mice Female BALB/c mice, 6-8 weeks, were purchased from Institute of Experimental Animals, Academy of Chinese Medical Sciences. All mice were maintained under specific pathogenfree conditions. The care, use and treatment of mice in this study was in strict agreement with guidelines in the care and use of laboratory animal manual set out by the Institute of Basic Medical Sciences. The protocol was approved by the Institute of Basic 2578618 Medical Sciences. All surgery was performed under sodium pentobarbital anesthesia, and all efforts were made to minimize suffering. 4: Flow cytometry Cells were stained with PE-, PE-Cy5-, or FITC-conjugated antibodies in PBS containing 0.1% sodium azide 23584186 and 2% FBS for 30 min on ice in the dark. Samples were washed once in staining buffer. Then the cells were fixed with 1% paraformaldehyde in PBS and preserved at 4 C. Isotype antibodies were included as negative control. Flow cytometry was carried out on a Becton-Dickinson FACSCalibur machine. 2: Reagents Epinephrine, isoproterenol, propranolol, mifeprostone, antalarmin, SC-236, lipopolysaccharide, and 
Brewer thioglycollate medium were purchased from Sigma Chemical Co.. Fetal bovine serum was purchased from HyClone Laboratories. Recombinant human Macrophage colony-stimulating factor was purchased from Cetus Corp.. All ELISA kits and PE-, PE-Cy5-, or FITC-conjugated antibodies against CD11b, Gr1, PD-L1, PD-L2, and FasL were purchased from eBioscience. Anti-PE microbeads, CD4+ T cell isolation kit II, anti-CD25 microbeads, and MS Columns were purchased from Miltenyi Biotech. Antibodies against cyclooxygenase 2 and -actin were from Santa Cruz Biotechnology. Image-iTTM live green reactive oxygen species detection kit, carboxyfluorescein diacetate succin