Analysis of MHC class I expression on stem cell lines at low temperature and in the presence of peptides. MaGSC 129/Sv and ESC 129/Sv MPI-II cells and as positive control RMA-S cells were cultured for 24 h at 37°C or at 28°C, in the presence of the H2Kb-binding peptide SIINFEKL (0.5 μg/ml) or a non-binding control peptide (con. pep.) NGLTLKNDFSRLEG. The culture at 28°C was either followed by a further incubation at 37°C for 2 h or not before flow cytometric analysis of H2Kb and H2Db cell surface expression. (A) An individual experiment with RMA-S and maGSC 129/Sv cell is shown by histogram overlays. The different experimental conditions are indicated by the colors of the lines. The H2Kb staining is indicated by full lines and staining with the isotype control by dotted lines. (B) The mean percentages of three independent experiments for H2Kb and H2Db positive cells + SD (staining with MHC class I mAbs minus isotype control) and the MFI + SD are given.