1ug of DNA-free RNA was run out on a non-denaturing gel to ensure equal concentrations of each sample followed by reverse transcription of 1 mg of each RNA sample using the iScript cDNA synthesis kit, following manufacturer's instructions (BioRad, Hercules, CA). 50 ng of cDNA was used to amplify HLA-DM, CIITA, gapdh, and Ii from each cell type to confirm expression. Forward and reverse primers sequences used in RT-PCR experiments indicated in Table S1 .