(a) Conventional secretory cells contain separate lysosomes and secretory granules. PC12 cells were transfected with the lysosomal protein CD63, tagged with GFP and costained with an antibody to secretogranin II, a secretory granule protein, in red. No overlap of the two compartments is observed. (b) Cells with secretory lysosomes package both lysosomal proteins and secretory proteins in the same compartment. A cytotoxic T lymphocyte is costained with the lysosomal membrane protein LAMP-2 (red) and the soluble secreted protein granzyme A (green). Extensive overlap of the two markers demonstrates colocalization in the same organelle (yellow).