Biochemistry of the phagosome: the challenge to study a transient organelle

Abstract

Phagocytes are specialized cells of the immune system, designed to engulf and destroy harmful microorganisms inside the newly formed phagosome. The latter is an intracellular organelle that is transformed into a toxic environment within minutes and disappears once the pathogen is destroyed. Reactive oxygen species and reactive nitrogen species are produced inside the phagosome. Intracellular granules or lysosomes of the phagocyte fuse with the phagosome and liberate their destructive enzymes. This process of phagocytosis efficiently protects against most infections; however, some microorganisms avoid their destruction and cause severe damage. To understand such failure of phagosomal killing, we need to learn more about the actual destruction process in the phagosome. This paper summarizes methods to investigate the biochemistry of the phagosome and discusses some of their limitations. In accordance with the nature of the phagosome, the issue of localization and temporal dynamics is emphasized, and recent developments are highlighted.

Keywords: Phagocytosis; ROS; fluorescent probes; pH; pathogen killing.

Figure 1

Cellular compartments in phagocytosis. The phagocyte contains multiple membrane-bound compartments, only some of them are included here. The vesicles mostly belong to the endosomal pathway. The neutrophil granules belong to several types with different content. Some of these compartments exchange membrane and liquid (arrows). The phagosome is filled with a pathogen (blue) surrounded by a limited phagosomal solution (red).