Introduction to Cells of the Immune System - Online Tutor, Practice Problems & Exam Prep

The immune system comprises various cells derived from hematopoietic stem cells in the bone marrow through hematopoiesis. These stem cells differentiate into common myeloid and lymphoid progenitor cells, leading to red blood cells (erythrocytes), platelets, and white blood cells (leukocytes). Leukocytes are crucial for immunity, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (monocytes, lymphocytes). Natural killer cells, T cells, and B cells play distinct roles in innate and adaptive immunity, highlighting the complexity of immune responses against pathogens.

Second-Line Defenses

In this video, we're going to begin our introduction to cells of the immune system. First, we need to recall from some of our previous lesson videos that the second line of defense of innate immunity actually involves two main types of cells. The first main type of cells are going to be the sentinel cells, and the second main type of cells are going to be the innate effectors. The sentinel cells are lookout or guard cells that are part of the censoring systems, which are important for sensing or detecting invading microbes. The innate effectors, on the other hand, create security responses that eliminate microbes identified by the scanning systems.

Notice down below on the left-hand side over here, we're showing you an image that we've talked about before in some of our previous lesson videos. We've already talked about the first line defenses, which are important for preventing microbe entry and serve somewhat as the security walls. These include the skin, mucus membranes, bodily fluids and chemicals, antimicrobial peptides, and the microbiome. So, we've already covered this in our previous lesson video.

Here in this video, we're beginning to talk about the second line of defense, which includes the scanning systems, as well as the innate effectors and the innate effector actions. The scanning systems are important for detecting the presence of microbes and damage and use sentinel cells. Cell communication, pattern recognition receptors, and the complement system are all components of the scanning system that we'll get to talk more about as we move forward in our course.

Over here, the innate effector actions are important for eliminating invaders. They serve somewhat as security soldiers that are important for eliminating invaders and include events such as phagocytosis, inflammation, fever, and the interferon response, all of which we'll get to talk more about as we move forward in our course. Notice over here we're showing you our map of innate immunity, and once again we've already talked about the first line defense mechanisms in our previous lesson videos, and so that's why they're grayed out here.

In this video, we're beginning to talk about the second line of defense. There are many different cells of immunity, and we'll get to talk more about those cells of immunity as we move forward. But they do include the sentinel cells that are part of the scanning systems that act as security cameras to detect microbes, as well as the effectors, the innate effectors that create innate effector actions that eliminate invaders and act as security soldiers. This here concludes our brief introduction to cells of the immune system, and we'll be able to talk more about the cells of the immune system as we move forward in our course. I'll see you all in our next video.

Hematopoeisis

This video, we're going to talk briefly about hematopoiesis. And so there are many different types of immune system cells that are developed from what we call stem cells. And so the process of hematopoiesis refers to the development of all blood cells from hematopoietic stem cells. And these hematopoietic stem cells are found specifically in our bone marrow, and so the bone marrow is where the process of hematopoiesis takes place. Now these hematopoietic stem cells are capable of differentiating into different types of cells to give rise to different types of blood cells. And so these hematopoietic stem cells are first going to differentiate into either a common myeloid or a common lymphoid progenitor cell. And so, these common myeloid or common lymphoid progenitor cells are then capable of differentiating into all other types of blood cells, and we'll be able to talk about those other types of blood cells as we move forward in our course. But if we take a look at our image down below, notice on the left hand side over here we're showing you a bone and the bone marrow. And within the bone marrow is specifically where the process of hematopoiesis takes place, the development of blood cells. And so notice that it starts with a hematopoietic stem cell, which we have right up here at the top, and this hematopoietic stem cell is capable of differentiating into different types of cells. It could differentiate either into a common myeloid progenitor cell, like what we see on the left, or it could differentiate into a common lymphoid progenitor cell, which we see over here on the right. And so the common myeloid progenitor cell is then capable of differentiating further into other types of cells, and, the same goes for the common lymphoid progenitor cell. And so we'll be able to talk about what the common myeloid and common lymphoid progenitor cells can differentiate into as we move forward in our course. But for now, this here concludes our brief lesson on hematopoiesis and hematopoietic stem cells, as well as and hematopoietic stem cells, as well as myeloid or lymphoid progenitor cells. And so I'll see you all in our next lesson video.

In humans, stem cells from which all blood cell types are developed are found in the:

• A. Peripheral circulation.
• B. Bone marrow.
• C. Lymphatic vessels.
• D. Lymph nodes.

Map of the Lesson on Cells of the Immune System

In this video, we're going to introduce our map of the lesson on cells of the immune system, which is down below right here. And so, we can go ahead and label the title of this map as "Cells of the Immune System". Now, what you'll notice is that all of these different cells of the immune system that you see down below right here are all derived from either a common myeloid progenitor cell or a common lymphoid progenitor cell. And of course, we know from our previous lesson video that the common myeloid and common lymphoid progenitor cells are derived from the hematopoietic stem cell found in the bone marrow.

Now, what you'll notice is that there are 3 major types of blood cells that are going to be differentiating from the common myeloid or the common lymphoid progenitor cells. And we've got those 3 major types of blood cells numbered down below. The first are going to be the red blood cells, which are also known as erythrocytes, and these red blood cells or erythrocytes are important for carrying oxygen gas or O₂ throughout the blood and delivering oxygen gas to all of our tissues. And so, if you take a look at our image down below, notice that the red blood cells or the erythrocytes are over here on the far left-hand side, and once again, they're derived from common myeloid progenitor cells. And they are important for delivering and transporting oxygen gas to our tissues.

Now, the second major type of blood cells is going to be the platelets, and these platelets are specifically important for blood clotting. And so, they will help to create blood clots in very specific scenarios. And so, notice down below right here we're showing you the platelets, and so, those platelets are once again important for blood clotting, and they're derived from common myeloid progenitor cells.

Now, the third main type of blood cells are going to be the white blood cells. And the white blood cells are also referred to as leukocytes, and these are going to be the cells that are important for the host's immune system. And so, if we take a look down below at our image, notice that the white blood cells, the leukocytes are all of these other cells that you see right here. These are all leukocytes, white blood cells important for immunity. And so, moving forward in our course, these cells here are going to be the ones that we're focusing on as we talk more about innate immunity and adaptive immunity as well.

And, what you'll notice is that these white blood cells can be further divided into other groups. They can be further divided into two groups specifically, the granulocytes and the agranulocytes. So notice that the granulocytes are over here in yellow. Okay. So these are leukocytes that are further grouped as granulocytes, and they include neutrophils, eosinophils, and basophils. Then, what you'll notice is that these others over here are all agranulocytes, and so, because they are agranulocytes, they are grouped differently.

Now moving forward in our course, we'll be able to differentiate what granulocytes and agranulocytes are, and we'll get to talk about all of these different cell types in a lot more detail. But for now, notice that the leukocytes are grouped as either granulocytes or agranulocytes. Then, another thing that's important to note is that these granulocytes, as well as the monocytes, macrophages, dendritic cells, and natural killer cells, these cells that are highlighted here in yellow are all part of innate immunity. And the only two cell types that are listed here that are part of adaptive immunity are going to be the T cells and the B cells. And so notice that they have, next to their little name, they have this little tiny red star, and that little tiny red star here represents that they are part of adaptive immunity. So only these two cells here are part of adaptive immunity, the T cells and the B cells.

Another thing to note here is that these natural killer cells, T cells, and B cells, are all referred to as lymphocytes. And so the natural killer cells are lymphocytes that are part of innate immunity, and the T cells and B cells are lymphocytes that are part of adaptive immunity. Now much later in our course, we'll get to talk a lot more about these T cells and B cells and adaptive immunity. But moving forward in the next set of immediate videos, we're going to be focusing mainly on the cells that are part of innate immunity, which are the ones that are highlighted here in yellow. And so this here concludes our brief lesson on the map of our lesson on the cells of the immune system. And as we move forward in our course, we're going to be focusing once again on these white blood cells, these leukocytes, and we'll start off by focusing on the leftmost branches first, talking about the granulocytes, neutrophils, eosinophils, and basophils. Then we'll move on to talk about the monocytes, macrophages, and dendritic cells, and then we'll move on to talk about the natural killer cells. And once again, the T cells and B cells, we'll talk about when we're talking about adaptive immunity after we finish talking about innate immunity. And so, I'll see you all in our next lesson video.

The hematopoietic stem cell has the ability to develop into which of the following cell types? 

1. Macrophage.  2.  Red Blood Cell.    3.  Neutrophil.        4.  B Cell.       5.  Dendritic cell.

• A. 2 & 4.
• B. 1, 2, & 5.
• C. 1, 3, 4, & 5.
• D. 1, 2, 3, 4, & 5.

Here’s what students ask on this topic:

What are the main types of cells involved in the second line of defense in innate immunity?

The second line of defense in innate immunity involves two main types of cells: sentinel cells and innate effectors. Sentinel cells act as lookout or guard cells, part of the scanning systems that detect invading microbes. They include components like cell communication, pattern recognition receptors, and the complement system. Innate effectors, on the other hand, are responsible for eliminating identified invaders. They perform actions such as phagocytosis, inflammation, fever, and the interferon response. Together, these cells form a crucial part of the body's immediate response to pathogens, acting as security cameras and soldiers to detect and eliminate threats.

What is hematopoiesis and where does it occur?

Hematopoiesis is the process of developing all blood cells from hematopoietic stem cells. This process occurs in the bone marrow. Hematopoietic stem cells can differentiate into either common myeloid progenitor cells or common lymphoid progenitor cells. These progenitor cells further differentiate into various types of blood cells, including red blood cells (erythrocytes), platelets, and white blood cells (leukocytes). The bone marrow serves as the primary site for this critical process, ensuring the continuous production of blood cells necessary for oxygen transport, blood clotting, and immune responses.

What are the differences between granulocytes and agranulocytes?

Granulocytes and agranulocytes are two categories of white blood cells (leukocytes). Granulocytes, which include neutrophils, eosinophils, and basophils, contain granules in their cytoplasm and are involved in innate immunity. They play roles in phagocytosis, inflammation, and allergic responses. Agranulocytes, on the other hand, lack visible granules and include monocytes, macrophages, dendritic cells, and lymphocytes (T cells, B cells, and natural killer cells). Agranulocytes are involved in both innate and adaptive immunity, with functions ranging from antigen presentation to direct pathogen elimination and immune memory formation.

What roles do T cells and B cells play in the immune system?

T cells and B cells are crucial components of adaptive immunity. T cells, which mature in the thymus, are involved in cell-mediated immunity. They can directly kill infected cells or help other immune cells by releasing cytokines. B cells, which mature in the bone marrow, are responsible for humoral immunity. They produce antibodies that bind to specific antigens on pathogens, marking them for destruction by other immune cells. Both T cells and B cells have memory capabilities, allowing for a faster and more effective response upon subsequent exposures to the same pathogen.

What is the function of natural killer cells in the immune system?

Natural killer (NK) cells are a type of lymphocyte involved in innate immunity. They play a critical role in the early defense against viral infections and tumor cells. NK cells can recognize and kill infected or abnormal cells without the need for prior sensitization to specific antigens. They do this by detecting changes in the levels of certain molecules on the surface of target cells. NK cells release cytotoxic granules that induce apoptosis (programmed cell death) in the target cells, helping to control infections and prevent the spread of cancerous cells.