Cells of the Immune System: Granulocytes - Online Tutor, Practice Problems & Exam Prep

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 and are involved in allergic reactions, while basophils release histamine to promote inflammation and recruit other immune cells. Understanding these cells enhances knowledge of immune responses and their roles 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, there are three main types of granulocytes that are named based on 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.

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, 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.

Notice that their nuclei have two to three lobes and they have these larger granules that stain a reddish color. And then the last type of granulocyte is going to be the basophils. And the basophils have a bifurcated nucleus, and they have larger granules that stain a darker blue, or purple color. Notice that they have a nucleus with two lobes and they have these larger granules that stain a purplish bluish color.

As we move forward in our course, we'll be able to talk a little bit more in detail 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 3 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. These neutrophils also will be able to migrate to different locations via the bloodstream, and they 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 going to be the first cells to be recruited to the site of infection or the site of 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 microbes 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 really interesting thing that these neutrophils can do is they can actually release neutrophil extracellular traps or NETs, which really act as webs of chromatin. They essentially release their own DNA into the environment to serve as a net or a trap that will once again trap infecting microbes in the DNA that they release. Trapping the microbes can be an important defense mechanism, focusing specifically on these neutrophils at the moment.

Notice that these neutrophils, again, they have these 5 lobes, they have these smaller granules that do not stain very well. Here's an image of what a neutrophil could look like under a microscope. Notice that here we're showing you an image of some kind of sharp object penetrating into the skin and penetrating tissue. When a sharp object penetrates into the tissue, it can create an area where microbes, pathogenic bacteria might be able to enter into our tissues. Notice that neutrophils are usually the first cells to respond to the injury and they're the first cells to be recruited to the site of infection or the site of damage.

Notice that these neutrophils, they travel through the bloodstream, and they're able to leave the bloodstream into the site of infection. These neutrophils are geared to fight the pathogenic microbes, to defend us from these pathogenic microbes. They can do this either via phagocytosis, where they can ingest microbes and degrade microbes. They can also, like what this neutrophil is doing, they can degranulate, which recall means they can release their cytoplasmic granules into the environment so that those cytoplasmic granules can act on those microbes and destroy the microbes, and they can also release those NETs or those neutrophil extracellular traps, or NETs that once again serve as webs of chromatin to trap infecting microbes.

Notice here in this image right here, we're showing you a neutrophil that is releasing its net, its web of DNA to trap the microbes. These neutrophils, another thing they can do is they can also recruit other immune cells to fight the infection. Notice that these, wandering macrophages are also being recruited to this area so that they can also help fight off these microbes that have invaded. This here concludes our brief lesson on neutrophils, and we'll be able to apply some of these concepts as we move forward in our course and also learn about the other granulocytes as well, 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. Now, 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.

Again, we're showing you an eosinophil here. This eosinophil is going to contain 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 the helminth you see right here. These eosinophils, again, 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. Once again, we'll be able to apply some of these concepts as we move forward, and then we'll get to talk a little bit about the last type of granulocyte, 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, 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, they can lead to degranulation and the release of histamine, and the histamine can lead to 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 are part of the innate immune system. There are three main types: neutrophils, eosinophils, and basophils. Neutrophils are the most abundant and are the first responders to infection, using phagocytosis and degranulation to destroy pathogens. Eosinophils primarily target parasitic worms and are involved in allergic reactions. Basophils release histamine to promote inflammation and recruit other immune cells. Understanding these cells is crucial for comprehending immune responses and their roles in health and disease.

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 enzymes through 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 primarily involved in defending against parasitic worms (helminths) and are also associated with allergic reactions. Their granules contain antimicrobial substances and enzymes that disrupt the membrane permeability of parasites, leading to their destruction. Eosinophils can also contribute to the symptoms of allergies by releasing substances that cause inflammation and other allergic responses. Understanding eosinophils' role is essential for studying parasitic infections and allergic conditions.

What is the function of basophils in the immune response?

Basophils play a crucial role in the immune response by promoting inflammation and participating in allergic reactions. They release histamine, a molecule that increases capillary permeability, allowing other immune cells to leave the bloodstream and enter infected tissues. This process helps recruit additional immune cells to the site of infection. Basophils are similar to mast cells, which are found in tissues and also release histamine to induce inflammation. Understanding basophils' function is important for studying inflammatory and allergic responses.

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

Neutrophil extracellular traps (NETs) are webs of chromatin (DNA) released by neutrophils to trap and neutralize pathogens. When neutrophils release NETs, they expel their own DNA into the extracellular environment, creating a net-like structure that ensnares microbes. This trapping mechanism helps to immobilize and kill pathogens, preventing their spread and aiding in the immune response. NETs are an important defense strategy employed by neutrophils to enhance their antimicrobial activity.