History and Importance of Phagocytosis
- Phagocytosis was first described by Albert von Kölliker in 1849.
- Ernst Haeckel provided the first direct evidence of phagocytosis by immune cells in 1862.
- William Osler noted phagocytosis in 1876.
- Élie Metchnikoff studied and named phagocytosis in 1880 and 1883.
- Phagocytosis played a significant role in establishing immunology as a scientific field.
- Phagocytosis is a key mechanism in the innate immune defense.
- It is one of the first responses to infection and can initiate an adaptive immune response.
- Professional phagocytes, such as neutrophils, macrophages, and dendritic cells, specialize in phagocytosis.
- Phagocytosis is present in both vertebrates and invertebrates.
- Most cells have the ability to perform phagocytosis.
- Phagocytosis helps eliminate harmful substances from the body.
- Phagocytosis is essential for defense against pathogens.
- Phagocytosis is involved in maintaining tissue homeostasis and clearing cellular debris.
- Phagocytosis activates the immune response.
- Phagocytosis has implications in various diseases and disorders.

Phagocytic Cells and Receptors
- Neutrophils, macrophages, monocytes, dendritic cells, osteoclasts, and eosinophils are professional phagocytes.
- Neutrophils patrol the bloodstream and quickly migrate to infected tissues.
- Neutrophils efficiently kill pathogens through intracellular killing and the release of microbicidal molecules.
- Macrophages form a resting barrier in tissues and continue phagocytosis by forming new lysosomes.
- Dendritic cells break down pathogens for antigen presentation to the adaptive immune system.
- Phagocytosis receptors can be divided into opsonic receptors and non-opsonic receptors.
- Opsonic receptors depend on opsonins, such as IgG antibodies or complement proteins.
- Non-opsonic receptors include lectin-type receptors, scavenger receptors, and Dectin receptor.
- Pattern recognition receptors (PRRs) can provide a second signal for phagocytosis through attachment to pathogen-associated molecular patterns (PAMPs).
- Receptors like Fcγ receptors, complement receptors, and mannose receptors play a role in initiating phagocytosis.

Phagosome and Degradation
- The actin-myosin contractile system facilitates the engulfment of material during phagocytosis.
- The phagosome is the organelle formed by phagocytosis.
- Phagosomes fuse with lysosomes to form phagolysosomes for degradation.
- Degradation can be oxygen-dependent or oxygen-independent.
- Oxygen-dependent degradation involves the production of reactive oxygen species.
- Oxygen-independent degradation involves the release of granules containing enzymes and antimicrobial peptides.

Phagocytosis in Protists and Mixotrophy
- Phagocytosis is used for feeding in many protists.
- Phagotrophic nutrition provides nourishment for protists.
- Protists like amoeba can phagocytose red blood cells.
- Ciliates also engage in phagocytosis in a specialised groove called the cytostome.
- Mixotrophy can involve both phagotrophic and phototrophic nutrition.
- Some protists exhibit mixotrophic behavior.
- Phagocytosis plays a role in obtaining nutrients during mixotrophy.
- Mixotrophic organisms combine phagocytosis and photosynthesis.
- Phagocytosis enhances the nutritional capabilities of mixotrophs.

Related Concepts and Processes
- Active transport is related to phagocytosis.
- Antigen presentation is another process involving immune cells.
- Phagocytosis is distinct from pinocytosis, a process of fluid uptake.
- Emperipolesis is a phenomenon where one cell engulfs another.
- Endosymbionts in protists can also be involved in phagocytosis.

Note: The content has been organised into 5 comprehensive groups based on the similarity of concepts and their relationships.

Phagocytosis (Wikipedia)

Phagocytosis (from Ancient Greek φαγεῖν (phagein) 'to eat', and κύτος (kytos) 'cell') is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is called a phagocyte.

In a multicellular organism's immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris. The ingested material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytised. Some protozoa use phagocytosis as means to obtain nutrients.