Phagosome

Phagosomes ( Fresskörperchen from Greek " phagein " = eat ) are large organelles inside the macrophages ( phagocytes ), which belong to the group of phagocytes. Phagosomes have to reduce the task of particles (eg bacteria or viruses) within the phagocytic enzyme and therefore play a crucial role in the immune system of eukaryotes.

Phagocytosis is a part of the immune defense.

Construction

Phagosomes have a diameter of about 250 nm, and are surrounded by a lipid bilayer (double lipid membrane).

Formation of phagosomes

Once the immune system detects an intruder within the system, the process of phagocytosis is initiated by the macrophages bind the exogenous particles per se. They surround the foreign body with its cell membrane and put together a so-called vesicles from inside the macrophage. This vesicle called the phagosome. The process of constriction and formation of the vesicle is called endocytosis ( into the cell / opposite of exocytosis ).

Effect

The phagosome is enriched after the pinch-off with acid and reactive oxygen and nitrogen species (ROS, RNS) by merging with the lysosomes of the cell, which also provide the necessary enzymes to degrade the phagosomal content. This complex formed from the phagosome and lysosome called secondary phagosome or phagolysosome.

Infection of the phagosome

Mycobacteria

Not according to plan, the infection with the tuberculosis pathogen Mycobacterium tuberculosis and other mycobacteria in connection with phagocytosis.

This pathogen has developed several mechanisms to survive in the phagosome can: first, it has a waxy, fat- rich cell wall that enables it to resist its destruction within the immune system. The phagosome is not able to split the outer layer of the cell wall of the pathogen. In addition, contains the outer wax layer lipoarabinomannan (LAM ), a glycolipid, along with a phosphatase signal transduction of the phagosome bothering you so this does not go the full destruction program. Furthermore, the bacterium several enzymes ( catalase, superoxide dismutase and others) resigned, turn off the any risk of reactive oxygen and nitrogen species. Most recently, the bacterium brings in a hibernation -like state in which there is no transcription or translation, and the organism lives on the back burner of their own fat layer. A result, many antibiotics are ineffective, which engage in otherwise normal cell processes.

The immune system binds the so-called Mycobacterium tuberculosis in granulomas, whereby the pathogen is not eliminated but only encapsulated. The infection thus remains a lifetime together and may at any time, even after several years, trigger an outbreak of the disease. About one- third of the world 's population is infected with the bacterial pathogen Mycobacterium tuberculosis.