Full text loading...
Chapter 14 : Acidification of Endosomes and Phagosomes
Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
The phagocytic pathway is a specialized endocytic pathway seen in cells that are capable of phagocytosis. Certain cells, such as macrophages and neutrophils, are termed professional phagocytes since they specialize in phagocytosis as a mechanism for cells to degrade unwanted material, which includes foreign particles such as bacteria, as well as necrotic or apoptotic host cells. Although the emphasis of this chapter is on the phagocytosis of pathogens, phagocytosis is in fact also essential for housekeeping functions in multicellular organisms, by way of clearing the apoptotic and necrotic cells. A comparative study of the properties of phagosomes containing Legionella pneumophila vs. Mycobacterium tuberculosis shows that whereas M. tuberculosis-containing endosomes exhibit several characteristics of early endosomes, such as a delayed clearance of major histocompatibility complex (MHC)-I molecules and a relatively intense staining for MHC-II and transferrin receptor, L. pneumophila phagosomes rapidly clear the MHC-I and do not express any of the endolysosomal markers studied. Several groups, using several different cell lines expressing exogenous cystic fibrosis transmembrane conductance regulator (CFTR), have reported that acidification of endosomes or the trans-Golgi network (TGN) are not affected by CFTR expression. In cases where phagosome acidification is needed for killing the pathogens, part of the function of acidification may be the activation of degradative lysosomal enzymes, which have low pH optima.
Key Concept Ranking
- Bacterial Proteins
Schematic representation of various organelles that participate in phagocytic and endocytic processes. Organelles are indicated in shades of gray to represent the degree of acidity. See text for references to studies from which the pH values were taken.