Fig. 3. Alanine scan of DRß cytoplasmic tail. HEK 293T cells were transiently co-transfected with the indicated mutant molecules and with pREP4 Iip35 LI/ML and tested after 48 hours. Cells were analysed by flow cytometry using BU45 either before (surface Ii) or after (total Ii) permeabilization with saponin. The ratios of surface to total Ii are shown. The total ISCR3 mean fluorescence value (MFV) for all the chimeric class-II molecules was between 242 and 260. The MFV for the secondary antibody alone was 5 (data not shown).