-dextran labels MHC class II–positive compartments in IFN-γ-treated WT and
mouse astrocytes. Fluorescence images of control (Ctrl.) and IFN-γ-treated (+IFN-γ) WT (a) and GFAP
-/- (b) astrocytes labeled with dextran, fixed, and immunostained with antibodies against MHC class II molecules. IFN-γ induces punctuate expression of MHC class II molecules. White pixels (mask) represent the colocalization mask of green (MHC II) and red fluorescence pixels (dextran). Note that the threshold value of 51 arbitrary units of 255 intensity levels, which corresponds to 20% of the maximum intensity level, was selected to separate the background intensity levels from the signal of single red and green pixels. Scale bars: 10 μm.