= Phagolysosome
A <phagolysosome> is a degradative, particle-containing compartment formed as a <phagosome> matures through interactions with <endosomes> and <lysosomes>. After <phagocytosis>, the engulfed particle can remain recognizable while its surrounding membrane and contents change. The particle's identity therefore does not establish the biochemical state of the whole compartment.<Biogenesis of phagolysosomes proceeds through a sequential series of interactions with the endocytic apparatus by M. Desjardins and others>[Abstract and Figures 5–7, sequential changes in latex-bead-containing compartments]{ref}
A useful experiment followed low-density latex beads taken up by J774 <macrophages>. The bead-containing compartments were isolated by flotation on a sucrose gradient. In a <pulse-chase analysis>, a limited uptake period followed by different waiting intervals yielded compartments of different ages. Comparing their proteins and <immunogold labeling> revealed changing membrane composition during maturation.<Biogenesis of phagolysosomes proceeds through a sequential series of interactions with the endocytic apparatus by M. Desjardins and others>[Figure 6 and Table I, LAMP2 immunogold labeling after the bead pulse and chase; Figures 5–7]{ref}
Normalization matters when interpreting such images. With invented counts, 10 gold labels along $5\,\mu\mathrm m$ of membrane give $2$ labels per micrometre; 20 labels along $20\,\mu\mathrm m$ give only $1$ label per micrometre. The second sample has more total labels but a smaller label density. Comparing membrane lengths prevents the amount of membrane observed from being mistaken for the abundance of its marker.
That measurement concerns localization of a membrane marker. It is not itself a measurement of luminal <pH>, degradation rate or killing of a <microorganism>. Those functions need corresponding observations: acquisition of one marker and completion of a degradative process answer different experimental questions.
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