Phagocytosis

Uptake, entrapment and digestion of foreign particles in a cell specialized for this process is called Phagocytosis designated. The inclusion of the particles takes place through the formation of cavities (phagosomes), which fuse with special vesicles, the lysosomes, after the particles have been absorbed. They contain the enzymes necessary for the digestion or breakdown of the trapped particles.

What is phagocytosis?

Phagocytosis is the term used to describe the intracellular digestive process of cells (phagocytes) that specialize in it. Phagocytosis includes the entire "eating process", which consists of the inclusion of the extracellular material to be digested and its breakdown or digestion.

The phagocytes flow around the material and enclose it in special cavities, the phagosomes. Small vesicles, called lysosomes, then combine with the phagosome to form the phagolysosome and provide their digestive enzymes with which internal digestion is initiated.

The material to be digested can be pathogenic bacteria, cells infected with viruses, metastatic cancer cells or cell debris from dead cells as well as fungi or fungal spores. Foreign substances and toxins that are in the bloodstream or that have penetrated the tissue are - if possible - rendered harmless by phagocytosis.

The particles that remain after phagocytosis are released by the phagocyte into the extracellular space, where the particles are usually taken up by the lymphatic system and passed through a collection point into the venous blood for further disposal.

The dendritic cells occupy a special position. They can also absorb pathogenic germs and foreign substances or pollutants, but they do not have the ability to phagocytize the substances ingested, but can only transport them in the intercellular space.

Function & task

Phagocytosis is used by the innate and acquired immune system for the decentralized fight against possible pathogenic germs, for the decentralized breakdown of the body's own dead cells and to kill the body's own cancer cells and cells infected with viruses. The phagocytes, which are capable of performing these tasks, are several types of granulocytes, white blood cells that are part of the innate or primary immune system and can take action without delay.

Phagocytosis is therefore used to fulfill several tasks and functions. An important task is to kill the pathogenic germs identified by the immune system and captured by the phagocytes and then to break them down in such a way that the substances that can still be used are made available to the body and the “indigestible” and unusable residues are excreted via the lymphatic system and the bloodstream can.

Another important task of phagocytosis is to break down the many dying or already dead body's own cells, to recover the reusable substances and to leave the useless rest to the lymphatic system for disposal. In addition to the phagocytes, certain tissue cells such as fibroblasts, endothelial cells and epithelial cells are capable of limited phagocytosis, which refers exclusively to the elimination of endogenous cell debris, to fulfill these tasks. As a result, the phagocytes are relieved and are more available for their primary task, the defense against pathogenic germs.

Phagocytosis performs a third important task and function as the immune system's “vicarious agent” in killing and breaking down the body's own cells if these have been identified by the immune system as dangerous tumor cells or cells infected with viruses. The cells are recognized using complex specific recognition patterns to which the phagocytes are programmed. The reactions of the phagocytes are controlled by cytokines, messenger substances to which the phagocytes respond with certain behaviors or activity patterns.

Illnesses & ailments

In connection with phagocytosis, which among other things serves to kill pathogenic germs, problems can arise because certain pathogens such as Mycobacterium tuberculosis (tubercle bacillus) are able to induce the phagocytes to phagocytose in order to get inside of the phagocytes without being digested. The germs can then multiply strongly within the phagocyte, as it were in its protection.

Other pathogenic germs that use phagocytosis for their own reproduction are the bacterial pathogens Salmonella enterica and Shigella flexneri. Both germs are ingested with spoiled food, and both pathogens synthesize specific protein mixtures which they inject into the phagocytes, causing them to form membrane protuberances which the germs then actively ingest. These bacteria also survive the attempt at phagocytosis undamaged and instead multiply under the protection of the phagocytes.

A serious limitation of the ability to phagocytosis can result from phagocyte defects. It is a reduction in the number of phagocytes, neutropenia or a restriction in the functionality of the cells, e.g. B. by a leukocyte adhesion defect (LAD). Both diseases can be primary, i.e. genetic, or acquired through infections or toxic substances - also as side effects of certain drugs.

So-called septic granulomatosis occurs when neutrophilic granulocytes, which are assigned to the primary immune system, actively absorb pathogenic germs, but the subsequent phagocytosis cannot kill the pathogens due to a genetic metabolic disorder.

Acquired or congenital disorders of the T lymphocytes have been implicated in various autoimmune diseases. In this case, the functional disorders of the T-lymphocytes can lead to the fact that they do not always recognize the body's own tissue or cells as the body's own. They attack the cells of certain types of tissue and then phagocytize them. A well-known viral disease associated with T lymphocyte dysfunction is AIDS.The disease is triggered by the HI virus and leads to a constant decrease in the number of T helper cells, so that in the advanced stage the immune defense becomes completely paralyzed.