What is phagocytosis?

Phagocytosis is a process where cells called phagocytes engulf other cells or particles. Phagocytes can be free-living organisms like amoebas or body cells like white blood cells. In animals, phagocytosis defends against infection and foreign substances (antigens). Phagocytes take in foreign particles by extending their cytoplasm into pseudopods, surrounding the particle, and forming a vacuole. Enzymes digest the ingested particle within the vacuole, and small organic components are used to build molecules needed by the cell.

Which cells in the body perform phagocytosis?

Phagocytosis is a process where cells called phagocytes engulf other cells or particles. Phagocytes are crucial for defending the body against infection and foreign substances. In humans, the most effective phagocytic cells are macrophages and neutrophils, both types of white blood cells. Macrophages are found in the lungs, liver, spleen, and lymph nodes, where they clear bacteria and other particles from the airways, blood, and lymph. Neutrophils, smaller phagocytes, travel in the blood and enter infected tissues. Other cells of the mononuclear phagocyte system , including monocytes and dendritic cells, also perform phagocytosis. Macrophages, monocytes, and dendritic cells form a first line of defense against harmful particles by engulfing foreign substances. Additionally, fixed cells in the lymph nodes, spleen, liver, and bone marrow cleanse the lymph and vascular systems by engulfing foreign material.

How does phagocytosis help protect the body from disease?

Phagocytosis is a crucial defense mechanism where cells called phagocytes engulf and ingest other cells or particles, such as bacteria , dust particles , and dead tissue cells . This process helps protect the body from disease by removing foreign substances and pathogens. During phagocytosis, the phagocyte extends its cytoplasm to surround the foreign particle, forming a vacuole where the ingested material is digested by enzymes. In vertebrates, macrophages and neutrophils are the primary phagocytic cells, working to clear the body of harmful bacteria and other foreign particles.

What are the basic steps involved in phagocytosis?

Phagocytosis is the process by which cells ingest other cells or particles. Adherence For phagocytosis to occur, the phagocyte and particle must connect. Sometimes opsonins , like complement and antibodies, create a surface film that helps phagocytes adhere to the particle. Engulfment The phagocyte then engulfs the particle by extending its cytoplasm around it, forming a vacuole called a phagosome. Digestion The phagocyte digests the ingested particle with hydrolytic enzymes, which are secreted into the vacuole. Small organic components of the particle are then used to build larger molecules needed by the cell.

What types of objects or particles do cells remove using phagocytosis?

Phagocytosis is a process where cells called phagocytes engulf other cells or particles. Phagocytes, such as white blood cells , remove a variety of objects and particles from the body, including bacteria , dead tissue cells , protozoa , dust particles , pigments , and other minute foreign bodies . Phagocytes also ingest worn-out or abnormal body cells.

How does phagocytosis relate to the immune system's response to infections?

Phagocytosis is a crucial process in the immune system's response to infections, acting as a defense mechanism against foreign invaders. Phagocytes, such as neutrophils and macrophages , are cells that ingest and sometimes digest foreign particles like bacteria, dead cells, or other debris. During infection, phagocytes engulf pathogens and initiate an inflammatory response, characterized by increased blood flow, redness, swelling, and fever, to eliminate the infection. The engulfment process involves adherence between the phagocyte and the particle, followed by the formation of a phagosome, where the ingested particle is digested by enzymes. Phagocytes also contribute to the adaptive immune response by presenting antigens to T lymphocytes, activating specific immunity.

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A four-step diagram shows a single-celled organism engulfing and digesting a food particle by phagocytosis, illustrating entrapment, vacuole formation, lysosome fusion, and digestion inside the cell.

Observe the human immune response phagocytosis

Examine stained images distinguishing phagocytes from bacteria during phagocytosis

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Key People:: Élie Metchnikoff; Karl Albert Ludwig Aschoff

Related Topics:: white blood cell; autophagy; macrophage; Kupffer cell; phagotrophy

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History

Early observations

The presence of foreign particles within cells was first described in the 1860s by pathologist Kranid Slavjansky. In the 1880s Russian-born zoologist and microbiologist Élie Metchnikoff introduced the term phagocyte in reference to immune cells that engulf and destroy foreign bodies such as bacteria. Metchnikoff also recognized that phagocytes play a major role in the immune response, a discovery that earned him a share of the 1908 Nobel Prize for Physiology or Medicine.

Types of phagocytes

The particles commonly phagocytosed by white blood cells include bacteria, dead tissue cells, protozoa, various dust particles, pigments, and other minute foreign bodies. In humans, and in vertebrates generally, the most-effective phagocytic cells are two kinds of white blood cells: macrophages (large phagocytic cells) and neutrophils (a type of granulocyte). Macrophages occur especially in the lungs, liver, spleen, and lymph nodes, where their function is to free the airways, blood, and lymph of bacteria and other particles. Macrophages also are found in all tissues as wandering amoeboid cells, and the monocyte, a precursor of the macrophage, is found in the blood.

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Characteristics of the Human Body

The smaller phagocytes are chiefly neutrophils that are carried along by the circulating blood until they reach an area of infected tissue, where they pass through the blood vessel wall and lodge in that tissue. Both macrophages and neutrophils are drawn toward an area of infection or inflammation by means of substances given off by the bacteria and the infected tissue or by a chemical interaction between the bacteria and the complement system of blood serum proteins. Neutrophils may also engulf particles after colliding with them accidentally.

Particle adherence

Before phagocytosis is accomplished, the phagocyte and the particle must adhere to each other, the possibility of which depends largely on the chemical nature of the surface of the particle. In the case of bacteria, if the phagocyte cannot adhere directly, protein components of the blood known as opsonins (e.g., complement and antibodies) form a surface film on bacteria—a process known as opsonization. Phagocytes adhere to the opsonins, and phagocytosis follows.

Encapsulated bacteria are ingested with more difficulty. In the absence of specific antibodies that recognize the bacteria, opsonization cannot occur, and the bacteria repel phagocytes. The surfaces of such bacteria are coated with special antibodies only after the body has mounted an immune response to the presence of that particular kind of bacterium. Such antibodies are of great importance in establishing immunity to diseases.

Particle engulfment and digestion

The speed with which a phagocytic cell ingests a particle varies somewhat with the size of the particle. Small particles, such as bacteria or minute grains of charcoal, are ingested almost instantaneously. Larger objects, such as clumps of bacteria or tissue cells, are phagocytosed over the course of a more-prolonged response. The cell flows around the object until it has been completely engulfed. The engulfed object is thus enclosed within a membrane-bound vacuole called a phagosome. The phagocyte digests the ingested particle with hydrolytic enzymes, which are contained within membrane-enclosed sacs called lysosomes found within the cell. Phagocytic enzymes are secreted into the vacuole in which digestion takes place. Small organic components of the particle are used to build larger molecules needed by the cell.

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