Linear ubiquitin chains are enriched in NEMO-containing foci in response to IL-1 and TNF. U2OS cells were left untreated or stimulated with IL-1 or TNF, as indicated. Cells were permeabilized with saponin before fixation and processed for the detection of NEMO (green) and linear ubiquitin chains (red) by immunofluorescence. Nuclei were stained with DAPI (blue). The insets in the images show magnified areas (indicated by the boxed regions). Bar, 5 µm.