Contribution of de novo synthesis to MHC II expression in maturing DCs. Splenic DCs were cultured for 4 hours in the absence (control) or presence of 5 μg/mL CHX or 10 μg/mL BFA, and analyzed by FACS. The sample labeled “Bckg” was not stained. Only live cells (PI^–) were included in the plots. Most of the MHC II molecules accumulating on the surface of maturing DCs are synthesized de novo.