SOCS-1 inhibits DC differentiation. (A) Murine bone marrow cells were forced to overexpress SOCS-1, SOCS-2, SOCS-3, or CIS by means of retroviral transfer of SOCS/GFP bicistronic constructs on days 1, 2, and 3 of the differentiation period. Cells were differentiated with GM-CSF for a total of 9 days and then analyzed for expression of CD11c by FACS either in the GFP-positive, transfected population or in the GFP-negative control population (mean+SD, n = 6, **P < .01). (B) FACS analysis of CD11c expression of one typical experiment from panel A either on mock (filled) or SOCS-1–transfected cells (open). Shown are overlay graphs for GFP-positive, transfected cells and GFP-negative control cells within one experiment.