Large pyramidal neurons in layer 5 of frontal cortex in 10-year-old individual with dup(15)/autism. Lysosomes identified by the presence of tripeptidyl peptidase I (TPP), characteristic for activated cells (using mAb 8C4), were detected in cells with more intense immunoreactivity for HNE. Up to 50% of these lysosomes immunoreacted strongly for HNE. Lipofuscin, detected as autofluorescent granules in green channel, contained strong reactivities for HNE and MDA, but most lipid peroxidation products were not located in lipofuscin. Bars 10 μm.