Fig. 6. Giant endosomes display early and late endosome/lysosome markers in RAW264.7 macrophages. To better confirm the nature of the large endocytic structures, rab5(Q79L)-expressing macrophages were grown on coverslips, fixed and probed with antibodies against different endosomal markers. Cells were then observed at the epifluorescence microscope. The early endosomal markers EEA1 and rabaptin-5 decorated large vesicles in a punctate pattern (arrows). The same phenomenon was observed with rab7, as well as with the recently described late endosome marker flotillin1. The large vacuoles were also positive for the late endosomal/lysosomal markers LAMP1 and LAMP2. However, these markers defined a continuous pattern around the large endosomes. Co-localization of rab5(Q79L) (designated as EGFP-rab5) with LAMP1 was observed using confocal fluorescence microscopy in cells expressing EGFP-rab5(Q79L). Arrowhead in the merge panel points at the section magnified in the inset, where arrows point at the yellow dots representing endosomal membrane domains on which EGFP-rab5(Q79L) and LAMP1 co-localize. n, nucleus; e, endosome. Bar, 10 µm.