Phagocytosis – Process with Definition, Steps & Examples (2023)

What is Phagocytosis

Phagocytosis combines two Greek words, where ‘phagein’ means ‘to eat’ and ‘kytos’ denotes ‘cell’.

It is a class of endocytosis where specific living cells ingest or engulf other cells or particles of size greater than 0.5 μm, forming a vesicular structure. The cell that performs phagocytosis is called a phagocyte, and the vesicular structure is called a phagosome.

Canadian physician William Osler first observed this phenomenon in 1876. It was later studied and named by Russian microbiologist Élie Metchnikoff (1880, 1883). In 1908, he received Nobel Prize for the same.

Phagocytosis differs from other methods of endocytosis due to its specificity. It depends on the ability of the cell to bind to the target through surface receptors. Both the cell and the foreign particle must be in physical contact for this process to occur.

What Cells Perform Phagocytosis

Most of the cells are capable of phagocytosis. However, several types of immune cells have specialization in this role.

Depending on their efficiency, the phagocytes are of two types.

a. Professional Phagocytes:They perform phagocytosis as their primary function. They have receptors on their cell surface, which help them to detect any pathogen. So, their primary role is to locate and engulf invading foreign organisms like bacteria and clear dead cells, thus protecting the body. White blood cells (WBCs), including monocytes, macrophages, neutrophils, dendritic cells, and mast cells, fall under this category.

b. Non-Professional Phagocytes:Cells like epithelial cells, endothelial cells, mesenchymal cells, and fibroblasts are classified as non-professional phagocytes as their principal function is not phagocytosis. For example, fibroblasts, which can phagocytose collagen in the process of remolding scars, can also make some attempts to ingest foreign particles. These types of cells lack efficient phagocytic receptors.

Does It Require Energy

Phagocytosis is a type of active transport mechanism as it requires the direct use of ATP to fuel the transport.

Where and When Does It Occur

Phagocytosis occurs in almost any tissue, most often in the bloodstream and interstitial space.

Major organs like lungs, liver, spleen, and lymph nodes, rich in macrophages, perform phagocytosis – for example, the Kupffer cells in the liver.

It is principally a defensive reaction against infection and invaded foreign substances (antigens). Therefore, it is used by the innate immune system when an infected cell is trying to destroy a foreign particle, like a virus. However, in a free-living single-celled phagocyte, such as an amoeba, this process is used as a means of feeding.

(Video) How do Immune Cells (Macrophages) Engulf Bacteria Phagocytosis Process

How does Phagocytosis Work

Phagocytosisis a complex phenomenon involving a cascade of multiple molecular mechanisms. So, the cells need to undergo specific steps in order to phagocytize something.


There are eight stages or steps involved in phagocytosis. They are described below:

Step 1: Activation of the Phagocyte

It is the first step of phagocytosis when the resting phagocytes become activated. During this phase, the phagocytes come close to some inflammatory mediators like bacterial proteins, capsules, peptidoglycan, prostaglandins, and complement proteins. As a result, the receptors on the cell surface bind to these molecules and cause the cells to respond.

Consequently, the phagocytes switch to a higher energy level. This phenomenon usually involves rearranging the cell cytoskeleton and swelling of the cell (caused by calcium and sodium ion influx).

Phagocytes also produce pattern recognition receptors (PRRs) which recognize and bind to pathogen-associated molecular patterns (PAMPs). PAMPs are components of pathogens and can include molecules like peptidoglycan and lipopolysaccharide (LPS).

Step 2: Chemotaxis of the Phagocyte

In the next step, the directional movement of the phagocyte occurs toward a higher concentration of molecules under the influence of a chemical attractant called chemotaxin. Bacterial products (e.g., endotoxin), injured tissues, complement proteins, and chemical substances produced by WBCs are typical examples of chemotaxin.

Activated cells express more glycoprotein receptors that help them reach the site of infections and bind firmly with microorganisms under the influence of cytokines.

Step 3: Attachment of the Phagocyte to the Pathogen

Here, receptors present on the cell surface of the phagocyte bind or adhere to the surface of the pathogen. This step is necessary for the ingestion of foreign particles. However, some bacteria can resist attachment, making it harder for the phagocytic cell to be taken into the cell and destroyed.

Different types of cells express different types of receptors; some are general, while some are specific. However, depending on the cell, there are mainly four types of surface receptors that play an essential role in phagocytosis (binding). They are given below:

Opsonin Receptors:These general transmembrane receptors are present on the cell surface of phagocytes (macrophages and neutrophils) and act via specific antimicrobial proteins called opsonins. In Greek, ‘opson’ means to ‘prepare for eating.’

(Video) Phagocytosis

These molecules enhance phagocytosis efficiency by phagocytic cells either by activating the complement pathway or marking the antigen with a specific antibody which makes it easier to recognize by the respective receptor. The process of coating pathogens to promote phagocytosis is called opsonization.

Scavenger Receptors:Scavenger receptors are a general type of Pattern recognition receptors (PRRs). Thus they recognize pathogen-associated molecular patterns (PAMPs) such as peptidoglycan, teichoic acids, lipopolysaccharide, mannans, flagellin, pilin, and bacterial DNA.

Macrophages widely express scavenger receptors (SRs). These receptors can bind to a diverse array of endogenous and non-self or foreign molecules.

Toll-like Receptors (TLRs):These receptors get their name from a similar receptor found in fruit flies (Drosophila melanogaster) encoded by the Toll gene. They are also a type of PRR and bind to specific molecules produced by bacteria, which activates the immune response.

TLRs have numerous roles. For example, they help recognize self and non-self antigens, detect invading pathogens, bridge innate and adaptive immunity, and regulate cytokine production, proliferation, and survival.

Antibodies:Some immune cells produce antibodies that can identify and bind to specific antigens, thus neutralizing or destroying the foreign object. Like Toll-like receptors, antibodies are also particular in their action, i.e., a particular antibody only act against a definite antigen. This feature is called antibody specificity.

Antibodies stimulate phagocytosis by coating the pathogen, making it more accessible to the phagocytes, thus playing a significant role in opsonization. Also, antibodies like IgM trigger the destruction of pathogens by stimulating the complement pathway.

Step 4: Ingestion of the Pathogen

After the attachment of the phagocyte to the pathogen, the cell begins to engulf the foreign particle. Then, the phagocyte starts extending the cytoplasm (pseudopods) as it surrounds the molecule to avoid the risk of membrane damage. As the cells are reasonably flexible and fluid, the pseudopods protrude outward on either side of the particle until both ends meet.

Step 5: Formation of Phagosome

When a pathogen or opsonin binds to a cell receptor, it triggers actin filaments within the cell. As a result, the actins get polymerized and form pseudopodia after the ingestion of the pathogen, which then surrounds the engulfed microorganism. These two protruding arms fuse, forming a vesicular structure called a phagosome. Finally, the phagosome transports the particle into the cell.

Step 6: Formation of Phagolysosome

Upon entering the cell, the phagosome fuses with a lysosome, becoming a phagolysosome. Lysosomes contain hydrolytic enzymes that help in the digestion of phagocytized particles. However, for phagocytes involved in immunity, unique structures called peroxisomes are produced to trap and remove toxic molecules.

(Video) Phagocytosis

Step 7: Destruction of the Pathogen

Phagolysosomes reduce the pH of their internal environment, making them acidic. This activity serves as an effective defense mechanism against microbes and provides a suitable medium for degradative enzyme activity.

As lysosomes contain the digestive enzyme called lysozyme and various antimicrobial and cytotoxic substances, they destroy the phagocytosed pathogen. The microbes are then killed either by oxygen-dependent (oxidative) or by oxygen-independent (non-oxidative) mechanisms.

Some other ways of destroying pathogens are using oxygen radicals, nitric oxide, antimicrobial proteins and peptides, and binding proteins.

Step 8: Elimination of Waste Materials

This is the final step of phagocytosis. Once the digested contents of the phagolysosome get neutralized, it forms a residual body containing the waste products. The wastes are then discharged from the cell by exocytosis, thus completing the process.

What Functions Does it Serve with Examples

Main Function

As discussed above, phagocytosis helps to protect us from the invasion of foreign particles such as bacteria, viruses, and protozoa and thus plays a vital role in the immune response.

Role in Apoptosis

Phagocytic cells remove apoptotic cells (dead cells) by efferocytosis. This process is known as the burying of dead cells. Both professional and non-professional cells can ingest dead cells. It plays a significant role in resolving inflammation and protecting tissue from harmful exposure to dying cells, inflammatory and immunogenic contents. It also contributes to tissue homeostasis.


Q1. Which activated T cells increase phagocytosis and antibody formation?

Ans. Helper T cells increase phagocytosis and antibody formation.

(Video) Phagocytosis: Definition, Steps, Role of ROS, Defects (HD)

Q2. What is the difference between autophagy and phagocytosis?

Ans. Autophagy is a process by which a cell removes its unnecessary or dysfunctional components in a regulated manner. It is performed by all cells. In contrast, phagocytosis is a cell’s defense mechanism that destroys a foreign particle like a virus or an infected cell. It is performed by immune system cells.

Q3. What is the difference between chemotaxis and phagocytosis?

Ans. Chemotaxis is the movement of organisms or cells towards or away from a chemical stimulus. On the other hand, phagocytosis is a mechanism used by immune cells and certain organisms to engulf infectious particles and destroy them.

Article was last reviewed on Thursday, February 2, 2023

(Video) Phagocytosis (FL-Immuno/10)


What is phagocytosis with example? ›

phagocytosis, process by which certain living cells called phagocytes ingest or engulf other cells or particles. The phagocyte may be a free-living one-celled organism, such as an amoeba, or one of the body cells, such as a white blood cell.

What are the 7 steps of phagocytosis? ›

Stages of Phagocytosis
  • Activation. Resting phagocytes become activated by inflammatory mediators (e.g. bacterial proteins, capsules, peptidoglycan, prostaglandins, complement proteins). ...
  • Chemotaxis. ...
  • Margination, Rolling and Adhesion. ...
  • Diapedesis. ...
  • Recognition-Attachment. ...
  • Phagocytosis.

What is an example of phagocytosis in the human body? ›

For example, foreign material in the lymph system is phagocytosed by fixed cells in the lymph nodes; similarly, the vascular system is cleansed by fixed cells in the spleen, liver, and bone marrow that engulf aged red blood cells and foreign bodies. Special cells in the lungs ingest dust particles.

Which step is the 3rd step in the 5 step process of phagocytosis? ›

The process of phagocytosis involves several steps: (1) particle recognition, (2) particle ingestion, (3) early phagosome formation, (4) late phagosome formation, and (5) phagolysosome formation.

Which of the following are examples of phagocytes? ›

The main types of phagocytes are monocytes, macrophages, neutrophils, tissue dendritic cells, and mast cells.

What are examples of phagocytosis and Pinocytosis? ›

Examples. Phagocytosis: Engulfment of bacteria by white blood cells and engulfment of food particles by cells are examples for phagocytosis. Pinocytosis: Uptaking of enzymes and hormones from the extracellular fluid is an example for pinocytosis.

What is an example of phagocytosis quizlet? ›

"Phagocytosis is the process of certain living cells, called phagocytes, ingesting or engulfing other cells or various particles" (Singh) The phagocytes can either be one-celled organisms, such as an amoeba. Phagocytes can also be body cells, for example a leukocyte or more commonly known as a white blood cell.

What are the steps of phagocytosis quizlet? ›

  • step 1 Chemotaxis. phagocyte is attracted or called towards infection.
  • step 2 Adherence. phagocyte attaches to microbe.
  • step 3 Ingestion. microbe is engulfed in "phagosome"
  • step 4 Phagolysosome formation. lysosome adds digestive chemicals.
  • step 5 Killing. ...
  • step 6 Elimination.

Which gives the steps of phagocytosis in proper order? ›

There are a number of distinct steps involved in phagocytosis:
  1. Step 1: Activation of the Phagocyte. ...
  2. Step 2: Chemotaxis of Phagocytes (for wandering macrophages, neutrophils, and eosinophils) ...
  3. Step 3: Attachment of the Phagocyte to the Microbe or Cell. ...
  4. Step 4: Ingestion of the Microbe or Cell by the Phagocyte.
Apr 9, 2022

What are some examples of Pinocytosis? ›

Examples of Pinocytosis

Microvilli in the gut use this process to absorb nutrients from food. Cells in the kidney can use pinocytosis to separate nutrients and fluids from the urine that will be expelled from the body. In addition, human egg cells also use it to absorb nutrients prior to being fertilized.

Where does phagocytosis occur in the human body? ›

Professional Phagocytes
Main locationVariety of phenotypes
Bloodneutrophils, monocytes
Bone marrowmacrophages, monocytes, sinusoidal cells, lining cells
Bone tissueosteoclasts
Gut and intestinal Peyer's patchesmacrophages
8 more rows

What are the 3 types of phagocytes? ›

They are a key component of the innate immune system. There are three main groups of phagocytes: monocytes and macrophages, granulocytes, and dendritic cells, all of which have a slightly different function in the body.

What are the 4 main steps of phagocytosis? ›

Phagocytosis can be divided into four main steps: (i) recognition of the target particle, (ii) signaling to activate the internalization machinery, (iii) phagosome formation, and (iv) phagolysosome maturation.

What is the definition of phagocytosis in biology? ›

Define phagocytosis.

Phagocytosis is the process by which living cells like phagocytes engulf or ingest particles or infected cells.

What are 3 examples of endocytosis? ›

The main kinds of endocytosis are phagocytosis, pinocytosis and receptor-mediated endocytosis, shown below.

What is difference between phagocytosis and pinocytosis? ›

Pinocytosis primarily refers to the uptake of extracellular fluids and small molecules by a cell, whereas phagocytosis is a process by which the cell membrane invaginates around large macromolecular structures (e.g., proteins and viruses) that are otherwise unable to diffuse into the cell.

What is an example of phagocytosis and identify cell type? ›

Describe an example of phagocytosis and identify the cell type involved. An example is when feeding in amoeba, neutrophilis and macrophages engulf foreign material and cell debris. They are white blood cells. [Logic: phagocytosis and pinocytosis are both part of endocytosis and these involve white blood cells].

What are the steps in pinocytosis? ›

Steps of Pinocytosis
  1. This triggers the cell membrane to create a fold around the fluid containing the molecules to be ingested.
  2. The cell membrane invaginates (folds back on itself) to create a pouch.
  3. This pouch is then pinched off at the cell membrane and can migrate into the cytosol of the cell.
Jun 16, 2022

What is pinocytosis vs endocytosis? ›

Endocytosis takes particles into the cell that are too large to passively cross the cell membrane. Phagocytosis is the taking in of large food particles, while pinocytosis takes in liquid particles. Receptor-mediated endocytosis uses special receptor proteins to help carry large particles across the cell membrane.

What is pinocytosis simple words? ›

Pinocytosis (Cell Drinking)

Pinocytosis (“pino” means “to drink”) is a process by which the cell takes in the fluids along with dissolved small molecules. In this process, the cell membrane folds and creates small pockets and captures the cellular fluid and dissolved substances.

What happens during phagocytosis? ›

Phagocytosis is the process of sensing and taking in particles larger than 0.5 μm. The particle is internalized into a distinctive organelle, the phagosome. This phagosome subsequently changes the structure of its membrane and the composition of its contents in a process known as phagosome maturation (3).

Which cells causes phagocytosis? ›

Macrophages initiate phagocytosis by mannose receptors, scavenger receptors, Fcγ receptors and complement receptors 1, 3 and 4. Macrophages are long-lived and can continue phagocytosis by forming new lysosomes. Dendritic cells also reside in tissues and ingest pathogens by phagocytosis.

What cell carries out phagocytosis? ›

In metazoans, phagocytosis is primarily carried out by specialized cells called professional phagocytes, which include cells of the immune system such as macrophages, neutrophils and dendritic cells [1].

What is the difference between phagocytosis and phagocytosis? ›

While phagocytosis involves the ingestion of solid material, pinocytosis is the ingestion of surrounding fluid(s). This type of endocytosis allows a cell to engulf dissolved substances that bind to the cell membrane prior to internalization.

What are the 3 types of phagocytes quizlet? ›

Phagocytes are specialised cells that identify, ingest and destroy pathogens. Neutrophils, macrophages and dendritic cells are phagocytes. They belong to the innate immune system.

What is phagocytosis explanation? ›

Phagocytosis is an important process for nutrition in unicellular organisms, while in multicellular organisms it is found in specialized cells called phagocytes. Phagocytosis consists in recognition and ingestion of particles larger than 0.5 μm into a plasma membrane derived vesicle, known as phagosome.

What does phagocytosis literally mean? ›

Phagocytosis: The process by which a cell engulfs particles such as bacteria, other microorganisms, aged red blood cells, foreign matter, etc. The principal phagocytes include the neutrophils and monocytes (types of white blood cells). The prefix "phago-" comes from the Greek "phago" meaning "to eat."

What is an example of pinocytosis? ›

Examples of Pinocytosis

Microvilli in the gut use this process to absorb nutrients from food. Cells in the kidney can use pinocytosis to separate nutrients and fluids from the urine that will be expelled from the body. In addition, human egg cells also use it to absorb nutrients prior to being fertilized.

What is phagocytosis and how does it work quizlet? ›

Phagocytosis is the process by which white blood cells, known as phagocytes, engulf and digest cells - thereby destroying them. These cells may be pathogens such a bacteria. Therefore, phagocytosis is one of the ways by which the immune system can protect the body from infection.

How does phagocytosis work quizlet? ›

Phagocytosis - the process by which particulate matter is engulfed and degraded by a cell. This is in contrast to endocytosis - a process by which soluble macromolecules are taken into a cell. a process by which soluble macromolecules are taken into a cell.

Which best describes phagocytosis? ›

The correct answer that describes phagocytosis is C. endocytosis of large undissolved particles, such as bacteria or large proteins. When molecules such as bacteria are phagocytized by cells, they will be packaged into membrane-bound vesicles.

What are phagocytes simple definition? ›

(FA-goh-site) A type of immune cell that can surround and kill microorganisms, ingest foreign material, and remove dead cells. It can also boost immune responses. Monocytes, macrophages, and neutrophils are phagocytes.

What cells function for phagocytosis? ›

Phagocytes include neutrophils, macrophages, and dendritic cells (DCs), which have the capacity to engulf and digest relatively large particles on the order of 1–10 µm and even larger. In adults, these cells are generated from hematopoietic stem cells in the bone marrow.


1. The Process Of Phagocytosis
2. Phagocytosis
(Professor Givon's Lectures)
3. Phagocytosis: Opsonization
(Ryan Abbott)
4. Phagocytosis
(Maureen Richards Immunology & Microbiology)
(Dr. Preeti Tyagi Lectures)
6. AS Biology - Phagocytosis (OCR A Chapter 12.5)
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