Cross-presentation of MP is dependent on protein processing by the proteasome and active transport into the ER via TAP. IDCs were preincubated with increasing doses of lactacystin. The lactacystin-pretreated DCs were cocultured approximately 12 hours with apoptotic or necrotic monocytes expressing MP together with the same doses of inhibitor and maturation stimulus (left axis). The ratio of dead cells to DCs was 2:1. Control DCs were pulsed with 100 nM MP peptide (right axis). All groups of DCs were fixed by glutaraldehyde, cultured with Flu16 and responses assessed by ELISPOT assay. The DC/T cell ratio was 2:1. One representative experiment of 4 is shown.