Phagocytosis

Phagocytosis ( from Ancient Greek φαγεῖν phagein "eat" and ancient Greek κύτος CYTOS "cell" ) refers to the active uptake of particles ( up to smaller cells ) in a single eukaryotic cell (as a form of endocytosis ). For phagocytosis both protists are capable of as well as those cells of a multicellular organism, which specialize in the intracellular digestion.

Protists

The incorporation can be done in single-celled organisms with a change in shape of the cell, for example by a flow around the foreign particles with pseudopodia ( pseudopods ) or by a Einstülpungsvorgang (called intussusception ) or without these by special organelles (transport to cytostome via buccal cavity in ciliates or by cytopharynx in ciliates and some Euglenozoa ). By phagocytosis the dropped objects are enclosed in food vacuoles, only then there is the actual digestion takes.

Mammals and humans

In mammals and in human medicine, the term phagocytosis is usually on the intake of larger particles by floating in body fluids specialized cells called phagocytes, based. Enveloping and destroying invading microorganisms by phagocytosis is an important part of the response of the cellular immune system. In addition, phagocytosis of disposing of dead ( apoptotic ) cells is necessary. In particular, the inclusion of pathogenic microorganisms by neutrophils is an important part of the body's immune defenses. Phagocytes recognize the pathogenic microorganisms on their specific surface structure ( for example, simple sugars - not to be confused with antigens ). Most phagocytosis - operated cells are phagocytes ( cells of the immune system such as macrophages or dendritic cells). The phagocytosed microorganisms are enclosed in vesicles, which then fuse with lysosomes and digested.

Certain pathogens make this mechanism advantage to penetrate by means of phagocytosis in macrophages and to be able to multiply there, for example, Mycobacterium tuberculosis, disease causative agent of tuberculosis. Two different mechanisms are generally distinguished: In the so-called zipper mechanism of pathogenic microorganism forms of cell adhesion molecules that are recognized by the receptor of the host cell (eg, a macrophage ) and trigger phagocytosis. The second mechanism is the so-called trigger mechanism. In this case, a bacterium injected into the phagocyte effector molecules (specific protein mixtures ), which bring to the host cell membrane protrusions to form and then to trigger phagocytosis.

Examples of pathogens are Salmonella enterica and Shigella flexneri. Often these agents are included with spoiled food.

Prerequisite for a successful phagocytosis is the specific recognition and binding by receptors on the cell surface. Foreign bodies such as bacteria or fungi can be eliminated by phagocytic cells on infection. Phagocytosis also plays a key role in the initiation of the adaptive immune response by supporting the release of proinflammatory cytokines. The binding of phagocytic targets lymphoid cells are attracted. In addition, professional antigen-presenting cells to antigen-specific lymphocytes present the antigenic peptides, they generate from the captured particles by limited proteolysis and activate it so.

Fibroblasts, epithelial cells and endothelial cells are not eating microbes in the situation. However, you can take up apoptotic cell body and thus contribute to the turnover of billions of cells that are discarded every day. Become antigens expose the danger signals phagocytosed so they trigger an inflammatory response. In contrast, apoptotic cells release in their phagocytosis from anti -inflammatory signals, which prevent further damage to the tissue. The large number of different phagocytes and phagocytes targets and the complexity of their interactions make it unlikely that the Phagozytoseprozesse run the same everywhere. Phagocytosis mediated by receptors. Since the nature of the captured particles by phagocytosis is very broad, there is the necessity of the existence of numerous different receptors for this process. Important in this context are the receptors for pattern recognition, for opsonins and for dead and dying cells.