Human monocytes were isolated from the peripheral blood of healthy adult donors and purified by centrifugal elutriation as previously described [9] . The experiments employing monocytes were repeated six times, each time with cells from a different donor. Monocytes were maintained in RPMI 1640 (Invitrogen) supplemented with 2 mM glutamine and 50 lg/ml of gentamicin. Samples were obtained in accordance with National Institutes of Health Institutional Review Board approved protocols. Macrophages were derived from blood monocytes by culturing the adherent cells for 7 days in RPMI 1640 supplemented with 2 mM glutamine, 50 lg/ml of gentamicin, and 2% human type AB serum (Sigma). Human monocyte-derived dendritic cells were generated by culturing blood monocytes in RPMI 1640 supplemented with 2 mM glutamine, 10 ng/ml of CSF2 (granulocyte macrophage colony-stimulating factor; R&D Systems), and 20 ng/ml of interleukin 4 (R&D Systems) for 7 days; the day before PSG1 treatment, 100 ng/ml of LPS (Sigma) were added to the cells.