Cells of the Immune System: Granulocytes: Study with Video Lessons, Practice Problems & Examples

Granulocytes are vital components of the innate immune system, comprising neutrophils, eosinophils, and basophils. Neutrophils, the most abundant leukocytes, respond first to infections, utilizing phagocytosis and degranulation to combat pathogens. Eosinophils primarily target parasitic worms, releasing antimicrobial substances. Basophils play a crucial role in allergic reactions and inflammation by releasing histamine, enhancing capillary permeability. Understanding these cells is essential for grasping immune responses and their implications in health and disease.

Granulocytes

In this video, we're going to begin our lesson on granulocytes, which are cells of the innate immune system. And so these granulocytes are white blood cells or leukocytes with visible cytoplasmic granules, which is really implied by their name. You can see the granules within their name. And so these granules are cell structures that contain compounds that are used for protective functions and are visible under a light microscope. Now really there are three main types of granulocytes that are named based off of the staining properties of their granules. And so the first main type of granulocyte is going to be the neutrophils, and the neutrophils actually have a nucleus with five lobes. So they have a five-lobed nucleus and they have really small granules which really do not stain very well. And so their granules remain somewhat of a neutral color, which is why they're referred to as these neutrophils. Now neutrophils are also sometimes referred to as polymorphonuclear neutrophils because poly is a root that means many, and morphonuclear is talking about a morphed nucleus. And so, these are abbreviated as PMNs. And so if we take a look at our image down below, notice over here on the left-hand side, we're showing you the granulocytes and, notice that we're showing you the neutrophils on the far left. And notice that they have a five-lobed nucleus and, their granules are so small that they don't stain very well. Now the next type of granulocyte that we have here are the eosinophils. And the eosinophils have two to three lobes in their nucleus, and they have larger granules that stain a reddish orange color. And so if we take a look at our image down below at the eosinophils, notice that their nuclei have, two to three lobes and they have these larger granules that stand a reddish color. And then the last type of granulocyte is going to be the basophils. And the basophils have a two-lobed nucleus, and they have larger granules that stain a darker blue, or purple color. And so if we take a look at the basophils down below over here, notice they have a nucleus with two lobes and they have these larger granules that stain a purplish bluish color. And so, if you take a look at our map over here on the left-hand side, notice that the granulocytes are right here, and they're derived from common myeloid progenitor cells, which again are derived from the hematopoietic stem cell. And notice that all of these other cell types that you see here from our map are all grayed out because we're not focusing on those cells at the moment. Now as we move forward in our course, we'll be able to talk a little bit more details about each of these different types of granulocytes, the neutrophils, eosinophils, and basophils. And so this here concludes our brief introduction to the granulocytes, and once again, we'll be able to learn more about them as we move forward. So I'll see you all in our next video.

Neutrophils

In this video, we're going to talk some more details about neutrophils. Recall from our last lesson video that neutrophils are one of the three types of granulocytes. These neutrophils are the most abundant type of leukocyte, or the most abundant type of white blood cell in the blood. In fact, they can make up to 70% of all leukocytes in the blood, which is the overwhelming majority. Neutrophils also will be able to migrate to different locations via the bloodstream and are able to respond to a site of infection or tissue damage. Usually, they are going to be the first to respond to an infection or tissue damage. So they are the first cells to be recruited to the site of infection or damage.

The granules that these neutrophils contain are going to have a variety of different antimicrobial peptides, including defensins, as well as hydrolytic enzymes that have the ability to degrade and destroy microbes. The granules themselves can also be released into the environment. This process of releasing the granules is referred to as degranulation. These granules can either be released through degranulation, or the neutrophil could destroy the microbes during phagocytosis. Phagocytosis is the process of ingesting and digesting material that has been brought in from the outside, and this includes invading microbes. Phagocytosis is sometimes referred to as cell eating.

Another interesting action that neutrophils can execute is the release of neutrophil extracellular traps or NETs, which act as webs of chromatin. They essentially release their own DNA into the environment to serve as a net or a trap, once again trapping infecting microbes with the DNA that they release. Trapping the microbes can be an important defense mechanism.

If we take a look at our image down below, notice on the left-hand side, we're showing you our map of the granulocytes, and we're focusing specifically on these neutrophils at the moment. Neutrophils have five lobes; they have smaller granules that do not stain very well, and here is an image of what a neutrophil could look like under a microscope. Notice in this image, we're showing you a sharp object penetrating the skin. When a sharp object penetrates the tissue, it can create an area where pathogenic bacteria might enter our tissues. Neutrophils are usually the first cells to respond to the injury and are the first cells to be recruited to the site of infection or damage. These neutrophils travel through the bloodstream and are able to leave the bloodstream to enter the site of infection.

Neutrophils are geared to fight the pathogenic microbes to defend us from these pathogens. They can do this either via phagocytosis, where they ingest and degrade microbes, or they can degranulate, which means they can release their cytoplasmic granules into the environment so that those granules can act on the microbes and destroy them. They can also release those nets, or those neutrophil extracellular traps, that once again serve as webs of chromatin to trap infecting microbes. Notice here in this image, we're showing you a neutrophil releasing its net, its web of DNA to trap the microbes.

Another thing neutrophils can do is recruit other immune cells to fight the infection. Notice that wandering macrophages are also being recruited to this area so that they can help fight off the microbes that have invaded. This concludes our brief lesson on neutrophils. We'll be able to apply some of these concepts as we move forward in our course and also learn about the other granulocytes, including eosinophils and basophils, as we move forward. I'll see you all in our next video.

Which granulocyte is the first to respond to an infection, has hydrolytic enzymes in its granules, and possesses the ability of phagocytosis?

• A. Basophil.
• B. Eosinophil.
• C. Neutrophil.
• D. Macrophage.

Eosinophils

In this video, we're going to briefly discuss eosinophils. Recall from some of our previous lesson videos that eosinophils are one of the three types of granulocytes, and the primary role of eosinophils is to protect against parasitic worms or helminths. The granules of these eosinophils actually have antimicrobial substances that bind parasites, and they also contain enzymes that disrupt the membrane permeability of those parasites. These eosinophils are geared to destroying and killing these parasitic worms or helminths that may try to invade and infect our bodies. Eosinophils can also be involved with the symptoms associated with allergies. We'll be able to talk a little bit more about allergies later in our course. But for now, take a look at our image down below on the left-hand side. Notice we're focusing on the granulocytes, specifically the eosinophils, which are derived from common myeloid progenitor cells. Again, these eosinophils, here we're showing you an eosinophil, and this eosinophil is going to contain these cytoplasmic granules that can stain a reddish color, and they can be released into the environment so that their antimicrobial substances and enzymes can help defend against parasitic worms such as this helminth that you see right here. Eosinophils are important for defending against parasitic worms and helminths and can also be important for some of the symptoms associated with allergies. This here concludes our brief lesson on eosinophils, and once again, we'll be able to apply some of these concepts as we move forward. Then we'll get to talk a little bit about the last type of granulocytes, the basophils. I'll see you all in our next video.

Basophils

This video, we're going to talk some more details about basophils. And so recall from some of our previous lesson videos that basophils are one of the 3 types of granulocytes. And so these basophils, like eosinophils, are also involved in allergic reactions. But the basophils are also really important for inflammation and the inflammation response during an infection. And so these basophils will produce a molecule known as histamine. And this molecule histamine is going to be released during inflammation, and it will promote inflammation by increasing capillary permeability or the permeability of the capillaries. And the permeability is how easily penetrable it is. And so this histamine molecule that is released by increasing capillary permeability, it will allow other defense cells to easily leave the bloodstream and enter into an infected area of the host so that they can help protect and defend the host.

Now, mast cells are cells that are very similar in function to the basophils. However, the mast cells are going to be found inside of the tissues. And so they are going to be found in many different types of tissues rather than circulating through the blood like what the basophils do. And so these mast cells, are going to be capable of detecting tissue damage, degranulating to release histamine, and again, the histamine can then induce inflammation. And so, notice down below in our image over here on the left-hand side, we're showing you our little map of the granulocytes focusing specifically on the basophils this time, which are derived from common myeloid progenitor cells. And so, the basophils, are going to be very similar to the mast cells. Once again, the basophils are going to be in the blood vessels, basically circulating through the blood. And so over here on this side of the image, we're showing you specifically the basophil. And the basophil is a granulocyte, so it's going to have the cytoplasmic granules that stain a bluish purplish color and they contain histamine and so upon degranulation, releasing this histamine, the histamine once again can lead to inflammation. And so notice that the mast cells are going to be very similar to the basophils except the mast cells are embedded in the tissues. And so you can see here the mast cells embedded in the tissues.

And, again, the mast cells are going to be able to detect specific types of antigens or allergens, molecules that can cause allergies. And, again, that can lead to degranulation and the release of histamine, and the histamine can lead to inflammation. And so these basophils, again, they are important for allergic reactions and also important for the inflammation response. And so this here concludes our brief lesson on basophils and mast cells, and we'll be able to get some practice applying some of these concepts as we move forward in our course. And so I'll see you all in our next video.

Which of the following is a phagocytic cell found in the human body?

• A. Eosinophil.
• B. Neutrophil.
• C. Basophil.
• D. T cell

Which of the following answers are characteristics or roles of granulocytes?

• A. Release of hydrolytic enzymes that damage bacterial cell membranes.
• B. Production and release of histamines which increases capillary permeability.
• C. Release antimicrobial substances that damage the membranes of parasites.
• D. Phagocytose invading microorganisms.
• E. All of the above.

White blood cells are referred to as _________.

• A. Platelets.
• B. Erythrocytes.
• C. Leukocytes.
• D. Megakaryocytes.

Two immune cells have very similar functions. Both immune cells release histamine and induce inflammation. However, _________ cells reside in specific tissues, while _________ cells travel through the blood stream.

• A. Mast cells; Basophil cells.
• B. Basophil cells; Neutrophil cells.
• C. Granulocyte cells; Basophil cells.
• D. Eosinophil cells; Dendritic cells.

In type I allergic reactions, antibodies are produced and bind to:

• A. Mast cells.
• B. Neutrophils.
• C. Eosinophils.
• D. Monocytes.

Granulocytes:

• A. Travel through the lymphatic system.
• B. Are the most numerous leukocyte in circulation.
• C. Develop in the thymus.
• D. Do not contain distinct granules in their cytoplasm.

Here’s what students ask on this topic:

What are the main types of granulocytes and their functions?

Granulocytes are a type of white blood cell with visible cytoplasmic granules, and they play a crucial role in the innate immune system. There are three main types of granulocytes: neutrophils, eosinophils, and basophils. Neutrophils are the most abundant and are the first responders to infection or tissue damage. They use phagocytosis and degranulation to destroy pathogens. Eosinophils primarily target parasitic worms and release antimicrobial substances to disrupt the parasites' membranes. Basophils are involved in allergic reactions and inflammation, releasing histamine to increase capillary permeability and facilitate the movement of other immune cells to the infection site.

How do neutrophils respond to infections?

Neutrophils are the first immune cells to respond to infections. They migrate to the infection site via the bloodstream and use several mechanisms to combat pathogens. They perform phagocytosis, ingesting and digesting microbes. They also release antimicrobial peptides and hydrolytic enzymes through a process called degranulation. Additionally, neutrophils can release neutrophil extracellular traps (NETs), which are webs of chromatin that trap and neutralize pathogens. These combined actions make neutrophils highly effective in the initial defense against infections.

What role do eosinophils play in the immune system?

Eosinophils are specialized granulocytes that primarily target parasitic worms (helminths). They contain granules filled with antimicrobial substances and enzymes that bind to and disrupt the membranes of these parasites, effectively killing them. Eosinophils are also involved in allergic reactions, contributing to the symptoms associated with allergies. Their ability to release these granules into the environment makes them crucial for defending against parasitic infections and managing allergic responses.

What is the function of basophils in allergic reactions and inflammation?

Basophils play a significant role in allergic reactions and the inflammatory response. They contain granules filled with histamine, which is released during inflammation. Histamine increases capillary permeability, allowing other immune cells to leave the bloodstream and enter the infected area more easily. This process helps to enhance the immune response. Basophils are similar to mast cells, which are found in tissues and also release histamine to promote inflammation. Both cell types are essential for managing allergic reactions and facilitating the body's defense mechanisms during infections.

What are neutrophil extracellular traps (NETs) and their function?

Neutrophil extracellular traps (NETs) are networks of chromatin (DNA) released by neutrophils into the extracellular environment. These traps act as webs that capture and neutralize pathogens, preventing their spread. NETs contain antimicrobial peptides and enzymes that can directly kill microbes. The release of NETs is a crucial defense mechanism, especially in situations where phagocytosis alone is insufficient to control the infection. By trapping and immobilizing pathogens, NETs enhance the overall effectiveness of the immune response.