Donor treatment with peg-G-CSF impairs T-cell function and induces regulatory T-cell activity. (A) C57BL/6 T cells from donors pretreated with control diluent, G-CSF 2 μg/d for 6 days, or peg-G-CSF 12 μg as a single dose at day -6 were stimulated with irradiated B6D2F1 peritoneal macrophages. Proliferation was measured at 72 hours by way of standard ³[H]thymidine incorporation assay as described in “Materials and methods.” P < .05 control versus G-CSF and P < .05 control versus peg-G-CSF. IFN-γ and IL-2 production were determined in culture supernatants by ELISA. (B) Control C57BL/6 T cells were stimulated with irradiated B6D2F1 macrophages as described earlier. Additional nonirradiated T cells from wild-type C57BL/6 donors pretreated with control diluent, peg-G-CSF 12 μg day -6, or IL-10^-/- donors pretreated with peg-G-CSF 12 μg day -6 were added at the doses shown. Proliferation was measured at 72 hours by way of standard ³[H]thymidine incorporation assay. ^*P < .05 control versus wild-type peg-G-CSF. (C) Control C57BL/6 T cells were stimulated with irradiated B6D2F1 macrophages as described earlier. Purified CD4⁺CD25⁺ T cells (nonirradiated) from wild-type C57BL/6 donors pretreated with control diluent or peg-G-CSF 12 μg day -6 were added at the doses shown. Proliferation was measured at 72 hours by way of standard ³[H]thymidine incorporation assay. (D) Whole spleen from control-, G-CSF-, or peg-G-CSF-pretreated donors as described earlier was stimulated with lipopolysaccharide (LPS) and cytosine-phosphate-guanosine (CpG), and IL-10 was measured in supernatants at 48 hours by ELISA. P = .0002 control versus G-CSF; P = .001 control versus peg-G-CSF. Data (A-D) are presented as mean ± SD of triplicate wells and represent one of 2 identical experiments.