SOCS proteins inhibit GM-CSF signaling. (A) Human monocytes were preincubated with 100 ng/mL LPS for the indicated time. Subsequently, cells were stimulated with 500 U/mL GM-CSF for 30 minutes and were analyzed for phosphorylation of STAT-5 by FACS (mean fluorescence intensity of untreated cells was set as 100%). (B) Murine RAW264.7 macrophages stably overexpressing the indicated SOCS proteins were stimulated with 100 ng/mL GM-CSF for 30 minutes. Cells were analyzed for phosphorylation of STAT-5 by FACS. Data are mean + SD.