Leukocytes - Online Tutor, Practice Problems & Exam Prep

Leukocytes, or white blood cells (WBCs), are crucial for immunity, defending against pathogens. They are categorized into granulocytes, which have visible cytoplasmic granules, and agranulocytes, which do not. Granulocytes include neutrophils, eosinophils, and basophils, each with distinct roles in immune responses. Neutrophils are the most abundant, responding first to infections. Eosinophils target parasitic infections, while basophils release histamine, promoting inflammation. Agranulocytes consist of monocytes, which can differentiate into macrophages and dendritic cells, and lymphocytes, including T cells and B cells, essential for adaptive immunity.

Introduction to Leukocytes

In this video, we're going to begin our introduction to leukocytes. Leukocytes are also known as white blood cells, and they can be abbreviated as WBCs. These leukocytes, or white blood cells, play a very important role in immunity to defend our bodies against pathogens, or disease-causing agents. Later in our course, we're going to do a very deep dive on immunity and many of its aspects. But for now, we're going to keep the focus specific to leukocytes and some fundamentals that you should know about them.

Unlike red blood cells or erythrocytes, white blood cells or leukocytes are not confined to the blood. Although white blood cells can be found in the blood, they can use the bloodstream to travel where they are needed in the body. Many white blood cells can actually migrate out of the bloodstream into the surrounding tissues to perform their functions, unlike red blood cells, which are confined to the bloodstream.

Leukocytes can broadly be categorized into two major groups based on their appearance under a light microscope after staining. These two groups are granulocytes and agranulocytes. The granulocytes, as their name implies, contain cytoplasmic granules that are easily visible under a light microscope. Agranulocytes, on the other hand, do not contain easily visible cytoplasmic granules. However, these cytoplasmic granules can still be present in agranulocytes but are not easily observed.

Let's take a look at our image, where we can piece some things together. Notice on the left-hand side, we have the same test tube that we've seen before in our previous lesson videos, showing the blood separated out into its three major components: the plasma, the buffy coat, and the erythrocytes. The white blood cells are present in the buffy coat region, which is why we are highlighting that buffy coat region to indicate that this is where the leukocytes can be found.

Leukocytes can be broadly categorized into two major groups based on their appearance under a microscope after staining. The first major group is the granulocytes. In all of these granulocytes, you can very easily see the cytoplasmic granules under the microscope after staining. Moving forward, when we discuss them, you can come back and fill in these interactive blanks for these three types of granulocytes that we'll discuss in more detail.

The second major group of leukocytes are the agranulocytes. There are several different types of agranulocytes that we are going to cover moving forward in our lesson. What you'll notice is that these agranulocytes do not have visible cytoplasmic granules inside of them, like what you could see with the granulocytes. This categorizes them into this group, agranulocytes. As we move forward and discuss more details about these agranulocytes, you can come back and fill in these interactive blanks that you see throughout.

This concludes our brief introduction to leukocytes, and moving forward we'll be able to apply these concepts and learn more about them. I'll see you all in our next video.

Leukocytes Example 1

So here we have an example problem that asks, which of the following statements about erythrocytes and leukocytes is false, and we've got these 4 potential answer options down below. Now option a says that leukocytes are significantly larger than erythrocytes. Now recall from back in our previous lesson videos that erythrocytes are actually relatively small cells, only about 7 micrometers in diameter, and most other body cells are much larger, 2 to 3 times larger in most cases, and that includes the leukocytes. And so to say that leukocytes are significantly larger than erythrocytes, this is actually a true statement. And because it's a true statement, it's not a false answer option that we're looking for, so we can cross off option a. Now option b says that leukocytes and erythrocytes are both confined to the bloodstream during normal function. And so, of course, we know from our last lesson video that this is actually not true. This is a false statement. Recall that erythrocytes, or red blood cells, are typically confined to the bloodstream to perform their normal function. However, leukocytes or white blood cells can actually migrate out of the bloodstream into surrounding tissues to perform their normal functions. And so, leukocytes are not confined to the bloodstream like erythrocytes are. And so because this is a false statement, that means that this is the false answer option that we were looking for, so we can indicate that option b is the correct answer to this problem. Now option c says that erythrocyte's primary function is transport, while leukocyte's primary function is protection. And of course, we know that this is a true statement, and, we know that erythrocytes are going to function primarily in the transport of gases, such as oxygen gas, for example, and some carbon dioxide gas. And we know that leukocytes or white blood cells, their primary function is in immunity to defend the body against pathogens, and so it does protect the body. Because this is true, it's not the false option that we're looking for, so we can cross off option c, and then of course because option b is false, we can also eliminate option d, which says all of the above are true. So again, b here is the correct answer. That concludes this problem, and I'll see you all in our next video.

What differentiates granulocytes from agranulocytes?

• A. a) Granulocytes contain cytoplasmic granules, but agranulocytes do not.
• B. Granulocytes contain cytoplasmic granules that can be easily visualized under a microscope after staining.
• C. Granulocytes are larger.
• D. Granulocytes are smaller.

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 3 main types of granulocytes that are named based on the staining properties of their granules.

The first main type of granulocyte are the neutrophils, and the neutrophils actually have a nucleus with 5 lobes. So, they have a 5-lobed nucleus, and they have really small granules which do not stain very well. And so, their granules remain somewhat of a neutral color, which is why they're referred to as neutrophils. 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.

If we take a look at our image 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 5-lobed nucleus, and their granules are so small that they don't stain very well.

The next type of granulocyte that we have here are the eosinophils. And the eosinophils have 2 to 3 lobes in their nucleus, and they have larger granules that stain a reddish-orange color. If we take a look at our image below at the eosinophils, notice that their nuclei have 2 to 3 lobes and they have these larger granules that stain a reddish color.

The last type of granulocyte is going to be the basophils. And the basophils have a 2-lobed nucleus, and they have larger granules that stain a darker blue, or purple color. If we take a look at the basophils below, notice they have a nucleus with 2 lobes and they have these larger granules that stain a purplish-blue color.

As we move forward in our course, we'll be able to talk a 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. 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. 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 their DNA. Trapping the microbes can be an important defense mechanism, focusing specifically on these neutrophils at the moment.

Notice that these neutrophils have five lobes, they have smaller granules that do not stain very well. Here's an image of what a neutrophil could look like under a microscope. Now, 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 here penetrates 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 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 and degrade microbes. They can also, like what this neutrophil is doing, 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 them, 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.

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 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. The granules of these eosinophils actually contain antimicrobial substances that bind parasites, and they also contain enzymes that disrupt the membrane permeability of those parasites. Eosinophils are geared towards 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 more about allergies later in our course. Here, we're showing you an eosinophil. 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 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. We'll be able to apply some of these concepts as we move forward, and then we'll get to talk a little 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 penetratable 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 leukocytes in circulation.
• C. Develop in the thymus.
• D. Do not contain distinct granules in their cytoplasm

Agranulocytes

So now that we've covered the granulocytes in our previous lesson videos, including the neutrophils, eosinophils, and basophils, in this video, we're going to focus on the agranulocytes. Recall that the agranulocytes are leukocytes or white blood cells with cytoplasmic granules that are not visible or easily visualized under a light microscope after staining. The agranulocytes include monocytes and lymphocytes. Moving forward in our course, we're going to talk more details about each of these different types of agranulocytes. Monocytes are cells that circulate in the bloodstream and can develop into either macrophages or dendritic cells. We'll talk more about macrophages and dendritic cells as we move forward in our course. The lymphocytes include B cells and T cells, and these cells are specifically involved in adaptive immunity. Once again, moving forward in our course, we'll be able to do a deeper dive on immunity and talk about many of its aspects, including adaptive immunity. But here we're reminding you that this will be covered in later videos, and for now, we're focusing on some fundamentals that you should be aware of when it comes to these agranulocytes.

Let's take a look at our image down below. This image is showing us the leukocytes, or white blood cells, which can be broadly categorized into these two major groups: the granulocytes, which we covered in our previous lesson videos, and the agranulocytes, which we are covering now. In granulocytes, you can clearly see those cytoplasmic granules within the cells, those little dots. With the agranulocytes, notice that you don't see those cytoplasmic granules inside those cells. The agranulocytes include monocytes, which are shown in the image here. Recall that these monocytes circulate in the blood and can differentiate into either macrophages or dendritic cells. We'll talk about these cells in more detail moving forward. The agranulocytes also include lymphocytes. The lymphocytes include B cells and T cells. These T cells and B cells are involved in adaptive immunity, which we'll cover in more detail later in our course. As you can see here in this image, the lymphocytes also include NK cells, these natural killer cells. These cells are considered lymphocytes but play a role in innate immunity, not adaptive immunity. We'll get to talk more details about these lymphocytes later in our course as we move forward. But for now, this here concludes our brief lesson on agranulocytes, and I'll see you all in our next video.

Monocytes

This video, we're going to begin talking about monocytes and the cells that derive from monocytes. And so these monocytes are or cellular eating or cellular eating. And so these two main types of cells are going to be the macrophages and the dendritic cells. Now the macrophages are, once again, phagocytic cells, meaning that they're capable of performing phagocytosis. And they also serve as sentinel cells, which we call are lookout or guard cells that act as scouts. And so these macrophages are capable of responding directly to an infection, to help eliminate an infection. But they can also alert other host defenses as well, and that is really what makes them sentinel cells. Now there are many different types of macrophages found in different types of tissues, and we refer to these macrophages as resident macrophages. And so resident macrophages, as their name implies, they reside permanently in specific tissues, which means that they remain stationary in the tissues, and they don't really migrate around to other tissues. They reside in the tissues. And so these resident macrophages, because they reside in the tissues, they will already be present in the tissues. Whenever those tissues get damaged and microbes, invade those tissues, they'll already be present and ready to respond because they reside permanently in those specific tissues. Now other macrophages we refer to as wandering macrophages. And as their name implies, they wander around or they move around through the blood to other sites of infection. And so these wandering macrophages can be recruited to a site of infection, and again, they travel around or wander around through the blood, circulate through the blood, and they can leave the bloodstream to a site of infection when they are recruited. Now giant cells refer specifically to macrophages that have fused together, and the fusion of macrophages, creates these giant cells. And the giant cells, because they have they consist of fused macrophages, they have increased destructive abilities. And so if we take a look at our image down below over here on the left-hand side, we're specifically focusing on the macrophages. And so, what you'll notice is that here we're showing you an image of the tissues, the skin here. And notice that the skin here has been damaged, that there's some kind of damage here, and, there's some kind of sharp object that has penetrated into the skin, and microbes are now infecting this, open wound. And notice that there are already some macrophages that are present in the tissues already. And we refer to these as resident macrophages because they reside, they are living in the tissues and they're already present and ready to respond whenever any of our tissues get infected. Now the wandering macrophages, and so the resident macrophages reside and remain stationary within a specific type of tissue, whereas the wandering macrophage can circulate through the blood and move to other locations and be recruited to sites of infection. Now, notice that, the second main type of cells that monocytes can develop into are going to be the dendritic cells. And dendritic cells also serve as phagocytic cells, but they are mainly going to be important as sentinel cells, which again are lookout or guard cells that act as scouts. And so their job is to sense and detect the signs of microbes. And then they can alert other immune system cells and activate other immune system cells. So these dendritic cells, they are sentinel cells with long appendages. And, they reside in tissues, and they are capable of alerting and initiating the adaptive immunity and adaptive immune responses. And so they can alert and activate B cells and T cells. And so, we'll be able to talk more about this process of dendritic cells alerting and initiating adaptive immunity later in our course when we're talking more about adaptive immunity. But ultimately here, what we're saying is that, these dendritic cells can ingest, pathogens in the tissues. And they can ingest those pathogens, break them down, and then present pieces of those pathogens, to cells of the adaptive immune system in order to activate those adaptive immune system cells. And so once again, we'll get to talk more about this later in our course, but down below we're showing you a little image of these dendritic cells. And so these dendritic cells have these long appendages, as you see here, that project out. And, here what we're showing you is an interesting image. Here is a, a micrograph of what these dendritic cells can look like under a microscope. Notice that they have these long appendages that stick out. Okay. And, notice here that we're showing you the intestinal lumen. So this is our, intestines, for example, our large intestine. And, some of the substances that we end eating get broken down into, antigens. And these antigens could be potentially from microbes that we have, eaten. And so, what you can see here is that the dendritic cells, which are, down below, they have these long appendages that can take little samples of the antigens in our intestine, and then they can ingest those antigens, break them down and process them, and then present them on their surface. So notice that these little pieces of antigen are presented on their surfaces, and here's a second dendritic cell doing something similar. And then these dendritic cells can go on to activate other adaptive immune system cells like B cells and T cells, which once again, we'll get to talk more about that process later in our course when we're focusing on adaptive immune system. But for now, this here concludes our brief lesson on the monocytes and how they can develop into macrophages and dendritic cells. And so we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

All of the following are major differences between macrophages & neutrophils except which of these answers?

• A. Macrophages can perform phagocytosis while neutrophils cannot.
• B. Macrophages kill microbes by "eating" them. Neutrophils kill microbes with hydrolytic enzymes and/or phagocytosis.
• C. Neutrophils circulate the bloodstream while resident macrophages reside in tissues.
• D. Neutrophils are granulocytes while macrophages are agranulocytes.

Monocytes can differentiate into which types of immune cells?

• A. Basophils & macrophages.
• B. Neutrophils & dendritic cells.
• C. Macrophages & dendritic cells.
• D. Mast cells & macrophages.

Introduction to Lymphocytes

In this video, we're going to begin our introduction to lymphocytes. Recall that these lymphocytes include leukocytes that are important for adaptive immunity. But really, we're focusing specifically on the T cells and B cells when we're talking about lymphocytes important for adaptive immunity. Now adaptive immunity is a topic that we'll get to talk a lot more about later in our course, and they will be covered in other videos. But really the 2 major groups of lymphocytes that are important in adaptive immunity are once again going to be the T cells and the B cells. And so the T cells and the B cells are going to be lymphocytes important in adaptive immunity, and that means that they are both going to respond to very, very specific antigens of invading microbes. And the specificity here is a characteristic of adaptive immunity. But once again, not all lymphocytes are part of adaptive immunity. And so what we need to note here is that, however, there are a group of lymphocytes, specifically the innate lymphoid cells, that differ from the B and T cells, because the B and T cells are part of adaptive immunity, but the innate lymphoid cells are actually part of innate immunity. And so the innate lymphoid cells are commonly abbreviated as ILCs for short, innate lymphoid cells. And they differ from the B and T cells due to a lack of specificity in the antigen recognition. And so whereas T cells and B cells are very, very specific and part of adaptive immunity, the innate lymphoid cells lack specificity. And so a classic example of ILCs or innate lymphoid cells are these natural killer cells, or for short, these NK cells or NKs. And, these natural killer cells are innate lymphoid cells, and they kill a variety of different cell types, so they are not specific to one type of antigen. They are going to be, not specific. And so, taking a look at this image that you see over here, notice that we're focusing specifically on the lymphocytes. And once again, the lymphocytes include natural killer cells, which are innate lymphoid cells that are part of innate immunity. But it also includes the T cells and the B cells, which are important for adaptive immunity and adaptive immune responses. So once again, we'll be able to talk a lot more details about the T cells and B cells later in our course when we're talking about the adaptive immune responses. And we'll also, while we're talking about the lymphocytes at that time, we'll also be able to talk a little bit more details about the natural killer cells as well later in our course in those separate videos. But for now, this here concludes our brief introduction to lymphocytes, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Why is a bone marrow transplant used to replace defective lymphocytes in a patient?

• A. Bone marrow creates common myeloid progenitor cells which differentiate into lymphocytes.
• B. Bone marrow creates monocytes which differentiate into lymphocytes.
• C. Bone marrow creates hematopoietic stem cells which differentiate into all immune cells including lymphocytes.

Which of the following immune cells is NOT a professional phagocyte?

• A. NK cells.
• B. Neutrophil.
• C. Macrophage.
• D. Dendritic cell.

Which of the following are referred to as mononuclear phagoytes?

• A. Lymphocytes and basophils.
• B. Mast cells and eosinophils.
• C. Basophils and eosinophils.
• D. Monocytes and macrophages.

Here’s what students ask on this topic:

What are leukocytes and what role do they play in the immune system?

Leukocytes, also known as white blood cells (WBCs), are crucial components of the immune system. They defend the body against pathogens, such as bacteria, viruses, and other disease-causing agents. Unlike red blood cells, leukocytes are not confined to the bloodstream; they can migrate into tissues to perform their functions. Leukocytes are broadly categorized into two groups: granulocytes and agranulocytes. Granulocytes, which include neutrophils, eosinophils, and basophils, have visible cytoplasmic granules and are involved in various immune responses. Agranulocytes, which include monocytes and lymphocytes, lack visible granules and play roles in both innate and adaptive immunity. Monocytes can differentiate into macrophages and dendritic cells, while lymphocytes include T cells and B cells, essential for adaptive immunity.

What are the differences between granulocytes and agranulocytes?

Granulocytes and agranulocytes are two major categories of leukocytes, distinguished by the presence of cytoplasmic granules. Granulocytes, which include neutrophils, eosinophils, and basophils, have visible cytoplasmic granules that can be seen under a light microscope after staining. These granules contain various enzymes and antimicrobial substances used in immune responses. Neutrophils are the most abundant granulocytes and are the first responders to infections. Eosinophils target parasitic infections, while basophils release histamine to promote inflammation. Agranulocytes, on the other hand, lack visible cytoplasmic granules. This group includes monocytes and lymphocytes. Monocytes can differentiate into macrophages and dendritic cells, which are involved in phagocytosis and antigen presentation. Lymphocytes, including T cells and B cells, are crucial for adaptive immunity.

What are the main functions of neutrophils in the immune system?

Neutrophils are the most abundant type of leukocytes, making up about 70% of all white blood cells. They are the first responders to sites of infection or tissue damage. Neutrophils migrate through the bloodstream and can leave the blood to reach the affected area. They perform several key functions: phagocytosis, where they ingest and digest invading microbes; degranulation, where they release antimicrobial peptides and enzymes from their granules into the environment; and the release of neutrophil extracellular traps (NETs), which are webs of chromatin that trap and neutralize pathogens. These mechanisms make neutrophils essential for the initial defense against infections.

How do eosinophils contribute to the immune response?

Eosinophils are a type of granulocyte primarily involved in defending against parasitic infections, such as helminths (parasitic worms). They contain granules filled with antimicrobial substances and enzymes that disrupt the membrane permeability of parasites, leading to their destruction. Eosinophils also play a role in allergic reactions by releasing substances that contribute to the symptoms of allergies. Their granules stain a reddish color under a microscope, making them easily identifiable. By targeting parasitic infections and participating in allergic responses, eosinophils are crucial for maintaining immune system balance and protecting the body from specific threats.

What is the role of basophils in the immune system?

Basophils are a type of granulocyte involved in allergic reactions and inflammation. They contain granules filled with histamine, a molecule that promotes inflammation by increasing capillary permeability. This allows other immune cells to leave the bloodstream and enter the infected area more easily. Basophils circulate in the blood, unlike mast cells, which are similar in function but reside in tissues. During an allergic reaction or infection, basophils degranulate, releasing histamine and other substances that contribute to the inflammatory response. This helps recruit additional immune cells to the site of infection or injury, enhancing the body's defense mechanisms.

What are the functions of monocytes and the cells they differentiate into?

Monocytes are a type of agranulocyte that circulate in the bloodstream and can differentiate into macrophages and dendritic cells. Macrophages are phagocytic cells that ingest and digest pathogens and debris. They also serve as sentinel cells, alerting other immune cells to the presence of an infection. Macrophages can be resident in specific tissues or wander through the bloodstream to sites of infection. Dendritic cells are also phagocytic and act as sentinel cells. They capture antigens from pathogens, process them, and present them to T cells and B cells, initiating adaptive immune responses. Both macrophages and dendritic cells are crucial for linking innate and adaptive immunity.