Peptide loading is faster in C282Y homozygous cells. (A) PBMCs without the C282Y mutation (control) or C282Y homozygous (C282Y) were ³⁵S-labeled during 5 minutes and chased for the indicated times. Half the lysates were incubated at 37°C and the other half maintained at 0°C. MHC class I complexes were recovered with W6/32 mAb and subjected to 10% SDS-PAGE. Molecular weight markers are shown on the left. Data shown represent one individual experiment using PBMCs from one WT blood donor and one C282Y homozygous patient with HH. Five experiments with similar results were done. (B) Percentage of peptide-loaded MHC class I molecules present at each chase time. Note the significant difference in the appearance kinetics of class I molecules when maintained at 0°C and after 37°C exposures. ^*Statistically significant difference between the C282Y mutants and the controls (P < .05). Data are representative of 5 independent experiments (each performed with PBMCs from one WT control blood donor and one C282Y homozygous patient with HH).