Fig. 2. Secretory lysosome labeled by transmembrane protein CD63-EGFP undergoes antigen-stimulated exocytosis as observed by confocal fluorescence microscopy. Vesicular secretion is characterized by the instantaneous loss of LysoTracker Red (LS) fluorescence (red) and flattening of the CD63-EGFP-labeled granular membrane (green) with the plasma membrane. The profile analysis shows a more gradual spreading of membrane bound fluorescence compared with release of LysoTracker Red. Blue, green, orange lines correspond to 0 seconds, 6 seconds and 9 seconds, respectively. Bars, 10 µm.