Introduction to Adaptive Immunity - Online Tutor, Practice Problems & Exam Prep

Adaptive immunity is a specialized defense mechanism that evolves over time, targeting specific pathogens through two main components: cell-mediated immunity, which utilizes T cells to combat intracellular pathogens, and humoral immunity, which employs B cells and antibodies to address extracellular threats. Primary lymphoid organs, like the thymus and bone marrow, facilitate the development of naive T and B cells, while secondary lymphoid organs, such as lymph nodes and the spleen, activate these cells upon encountering antigens, leading to effective immune responses.

Adaptive Immunity

In this video, we're going to begin our introduction to adaptive immunity. Now, unlike innate immunity, which we've covered in our previous lesson videos, adaptive immunity, as its name implies, includes components that adapt or change over time in order to become better suited and provide better immunity over time. And that's an idea that we'll get to talk a lot more about as we move forward in our course. Also, unlike innate immunity where each individual component protects against a broad range of pathogens, here with adaptive immunity, each individual component only protects against very specific pathogens, which is also why adaptive immunity is sometimes referred to as specific immunity. Once again, we'll be able to talk a lot more details about the adaptation and the specificity of the adaptive immune system as we move forward in our course. Adaptive immunity is considered a dual system with 2 components, and really, there are 2 categories within adaptive immunity. The first major category is going to be cell-mediated immunity, and the second major category of adaptive immunity is humoral immunity.

Cell-mediated immunity is going to be targeting and destroying intracellular pathogens or pathogens that are inside of a host cell using T cells, and these T cells are going to be T lymphocytes. They're a specific type of immune system cell that we'll get to talk a lot more about as we move forward in our course. These T cells, they use T cell receptors or TCRs for short. And these TCRs are membrane proteins that serve as receptors, and they use them to generate an immune response. Again, we'll get to talk a lot more details about the immune responses that T cells are capable of generating as we move forward in our course.

Again, the second major category of adaptive immunity is humoral immunity. Humoral immunity is going to be targeting and destroying extracellular pathogens or pathogens that are on the outside of the host cell. Rather than using T cells, like what cell-mediated immunity uses, humoral immunity is going to use B cells, and they're also going to use antibodies. Once again, we'll get to talk a lot more details about B cells and antibodies as we move forward in our course. Now these B cells, unlike the T cells, they use B cell receptors instead of T cell receptors. And these B cell receptors can be abbreviated as BCRs. And they use these BCRs to generate an immune response. Once again, we'll get to talk about the different types of immune responses that B cells are capable of generating as we move forward in our course.

But for now, if we take a look at our image down below, you can see the 2 major categories of adaptive immunity. On the left-hand side, we're showing you an image focusing on cell-mediated immunity, which again is going to be targeting and destroying intracellular pathogens such as for example, a virus that has infected a cell and is an intracellular pathogen. Notice that cell-mediated immunity uses T cells like what we're showing you over here. These T cells contain TCRs, T cell receptors. And those are what these little pink molecules are on the surface, the TCRs. The TCRs are going to be what allows the T cell to generate an immune response to a very specific pathogen.

On the right hand side, we're showing you an image of humoral immunity. Humoral immunity once again is going to be targeting and destroying extracellular pathogens such as for example, these bacteria or microbes that are on the outside of a cell, floating around in the extracellular environment. Unlike cell-mediated immunity, humoral immunity is going to use B cells and antibodies. Notice over here on the left-hand side, we're showing you a B cell, and these B cells can ultimately eventually change in order to be able to release antibodies. And that's a process that we'll get to talk more about later in our course as we move forward. Now, these B cells, instead of containing TCRs, they contain BCRs, B cell receptors. And that's what these molecules are on the surface. And what you'll notice is that these BCRs on the surface of B cells, they resemble the antibodies that they ultimately release. Once again, we'll talk about how these antibodies and B cells can generate immune responses as we move forward in our course.

But for now, this here concludes our brief introduction to adaptive immunity and its 2 components, cell-mediated immunity and humoral immunity. We'll be able to get a lot more practice applying these concepts and learning a lot more about adaptive immunity as we move forward in our course. And so I'll see you all in our next video.

Cytotoxic T cells are primarily involved in ____________.

• A. Innate Immunity.
• B. Antibody production.
• C. Cell-mediated Immunity.
• D. Humoral Immunity.

The humoral response is initiated by production of:

• A. Cytotoxic T cells.
• B. Antigens.
• C. Red blood cells.
• D. Antibodies.

Primary vs. Secondary Lymphoid Organs

In this video, we're going to continue to talk about adaptive immunity by introducing and differentiating primary versus secondary lymphoid organs. And so first we need to recall from some of our previous lesson videos that T and B lymphocytes, or T and B cells, are the primary cells involved in adaptive immunity. Where T cells are important for cell-mediated immunity, and B cells are important for humoral immunity. Now, the primary lymphoid organs are the specific organs within our bodies where immature T and B lymphocytes develop into their naive forms. And these naive T and B lymphocytes are really just inactive T and B lymphocytes. And so the naive T and B lymphocytes are fully developed, but they have not yet encountered the specific antigen that they respond to. And so they remain in their inactive forms when they are naive. However, whenever these naive T and B lymphocytes are introduced to their specific antigen, the naive T and B lymphocytes can become activated, and the activated T and B lymphocytes can go on to generate immune responses, which we'll get to talk a lot more about this process as we move forward in our course. Now these primary lymphoid organs are where the immature T and B lymphocytes develop into naive forms. And the primary lymphoid organs include the thymus, which is where the T cells develop. And so you can see the T in thymus can help remind you that this is where T cells develop. And, the bone marrow is also a primary lymphoid organ, and the bone marrow is specifically where B cells develop. And so the B in bone marrow can remind you of the B in B cells. Now although T cells develop in the thymus and B cells develop in the bone marrow, it is important to note that both the T and B lymphocytes are actually initially produced in the bone marrow together. However, the T cells will go on to migrate from the bone marrow to the thymus where they will fully develop, and the B cells remain in the bone marrow to fully develop.

Now the secondary lymphoid organs, on the other hand, are organs where the naive or inactive T and B lymphocytes can become activated. And the activated T and B lymphocytes can then begin their immune functions, which we'll get to talk about their immune functions in more detail as we move forward in our course. Now in other words, we can say that these secondary lymphoid organs are specific sites within our bodies where foreign molecules or foreign antigens are brought into contact with large populations of naive lymphocytes, activating those naive lymphocytes so that they can begin their immune functions. Now the secondary lymphoid organs include the lymph nodes, the spleen, and tonsils. Notice that the primary lymphoid organs are going to have the number 1 next to them and the secondary lymphoid organs are going to have the number 2 next to them in this image. And so, once again recall that the organs include the thymus, which is where the T cells are going to fully develop. Notice that the thymus is the specific organ that is right above the heart as you see right here. The primary lymphoid organs also include the bone marrow. And the bone marrow again is where the B cells are going to fully develop. But once again, don't forget that both T and B cells will be initially produced in the bone marrow, but then the T cells migrate to the thymus to fully develop, whereas the B cells remain in the bone marrow to fully develop.

The secondary lymphoid organs once again include the tonsils, spleen, as well as our lymph nodes. And so this here concludes our brief introduction to primary and secondary lymphoid organs, 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.

T cells and B cells are produced in the:

• A. Bone marrow.
• B. Thymus.
• C. Bloodstream.
• D. Epithelial Cells.

T cells mature in the __________ & B-cells mature in the ____________.

• A. Bone marrow; Thymus.
• B. Thymus; Bloodstream.
• C. Hypothalamus; Bone marrow.
• D. Thymus; Bone marrow.

The secondary lymphoid organs:

• A. Are where foreign antigens interact with lymphocytes.
• B. Are the site of antibody production.
• C. Are hematopoietic.
• D. Include bone marrow & thymus.

Which of the following are two of the secondary lymphoid organs?

• A. Stem cells & Spleen.
• B. Lymph Nodes & Bone Marrow.
• C. Lungs & Bone Marrow.
• D. Spleen & Lymph Nodes.

Map of the Lesson on Adaptive Immunity

In this video, we're going to introduce our map of the lesson on adaptive immunity, which is down below right here. And so because this image does represent a map, you can use it like a map to help guide you through our lesson moving forward. And so you can think of this map as a table of contents that includes the topics that we're going to cover and the order that we're going to cover them in. And so the way that this map works is that it starts over here on the left-hand side and, you follow the branches that are at the top first and then you go down and you explore the branches in this particular order, and you make your way downwards. And so that is the order that we're going to be covering these topics. And so notice that on the far left what we have is adaptive immunity, and that's because remember this is a map of the lesson on adaptive immunity. And so the very first thing that we're going to talk about moving forward after this is antigens. And we're going to talk about what they are and, talk more details about them. After we talk about antigens, then again, we're going to be following the topmost branches first. So we'll talk about the lymphocytes in more detail, specifically the T and B lymphocytes or the T cells and the B cells. First we're going to talk about the T cells first. And there are two main types of T cells that we're going to talk about, the cytotoxic T cells as well as the helper T cells. After we finish talking about the T cells, then we'll move on to talk about the B cells, and how B cells can differentiate into other types of cells called plasma cells. And these plasma cells are capable of secreting or releasing antibodies. And there are five major classes of antibodies that we're going to talk about moving forward including IgG, IgA, IgM, IgE, and IgD. Then we'll get to talk about a process called class switching, which applies to these B cells. And then we'll talk about B cell activation via T dependent antigens as well as T independent antigens. Then after we talk about the T cells and the B cells, we'll move on to talk about clonal selection which applies to both T cells and B cells. And then we'll also get to talk a little bit about affinity maturation as well. Then after we finish talking about the lymphocytes and all those details, we'll move on to talk about immune responses, specifically the primary immune response and the antibodies that are involved with that, and the antibody concentrations that are involved with that, as well as the secondary, immune response and again the concentration of antibodies that are involved with that as well. After we talk about these immune responses, the primary and secondary immune responses, then we'll talk about tolerance mechanisms. Specifically central tolerance and peripheral tolerance. And then last but not least, we'll wrap up our lesson talking about these natural killer cells or NK cells. And so, really this here is our map of the lesson, and again we'll be covering these topics in the particular order that we talked about them here. And so you can reference this map as we move forward to help guide you and to help you figure out where we are within the lesson. And so this here concludes our brief introduction to our map of the lesson on adaptive immunity and I'll see you all in our next video.

Overview of Adaptive Immunity

In this video, we're going to do a brief overview of adaptive immunity. However, it's important to keep in mind that all the information that we're going to talk about in this video, we're going to explain and break down in a lot more detail as we move forward in our course. And so if you're a little bit confused in this video, that's okay because again, we'll explain and break it down in a lot more detail moving forward. Now, taking a look at this image down below, this image is going to help us with our overview of adaptive immunity. And one thing to note is that we have these different colored boxes. Notice that this box that we have at the top right here, this box here, represents our primary lymphoid organs, which recall includes the thymus and the bone marrow. And then the next box that we have, which is down below here in green, this box represents our secondary lymphoid organs which you might recall include organs such as your tonsils and your spleen and lymph nodes. Those are all examples of secondary lymphoid organs. And then notice that we have the yellow that surrounds all of this, and, this yellow that surrounds all of this is referred to as the surrounding tissues. Okay, just broadly defined as the surrounding tissues that are around the primary and secondary lymphoid organs. And so, what you'll need to recall from our previous lesson videos is that again the primary lymphoid organs include the thymus and the bone marrow. T cells fully develop in the thymus and B cells fully develop in the bone marrow. And what you'll notice is that these primary lymphoid organs when they are fully developed they start off as naive T cells and naive B cells. Recall that the naive just refers to the fact that they are inactive and that they have not yet encountered the specific antigen that they respond to. Now there are two types of T cells. There are cytotoxic T cells or T_C cells and there are also helper T cells or T_H cells. And, what you'll notice is that the T cells, regardless if they are cytotoxic or helper T cells, they must become activated in order to carry out their immune responses. And activation of the T cells is actually going to occur through an antigen-presenting cell such as a dendritic cell. And that's what's being shown here in the middle. A dendritic cell that is actually presenting antigens to the cytotoxic T cell as well as to the helper T cell. And, under the right conditions, these naive T cells, whether they're cytotoxic or helper, will become activated. And the activation of these T cells allows them to differentiate into either effector cytotoxic T cells or memory cytotoxic T cells. And the same goes for the helper T cells. They can differentiate into effector helper T cells or differentiate into memory helper T cells. And the memory cells are all-important for generating a secondary immune response when you are exposed to an antigen for a second time. Whereas the effector cells are important for generating an immune response ASAP. Now, what you'll notice is that these effector helper T cells, they play a role in helping to activate B cells. And so notice that the B cell here is starting off as a naive B cell, an inactive B cell that has not yet encountered its antigen. But when it does encounter its antigen, it can, essentially present that antigen to a helper T cell. And the helper T cell can then go on to activate the B cell. And the activated B cell once again can either differentiate into memory B cells, important for a secondary immune response, or the activated B cell could differentiate into plasma cells. And the plasma cells can directly secrete antibodies, and the antibodies will, carry out some kind of immune response. And so all of these ideas that we've talked about and mentioned here in this video, again we're going to explain them and break them down in a lot more detail as we move forward in our course. And again, keep in mind that this was just an overview of the adaptive immune system lesson. And again, we'll be able to talk more about this moving forward. So I'll see you all in our next video.

What major advantage is conveyed by having a system of adaptive immunity?

• A. It enables a rapid defense against an antigen that has been previously encountered.
• B. It enables an animal to destroy most pathogens almost instantly the first time they are encountered.
• C. It results in effector cells with no tolerance to host or self-antigens.
• D. It allows for the destruction of antibodies.

Here’s what students ask on this topic:

What is the difference between cell-mediated and humoral immunity?

Cell-mediated immunity and humoral immunity are the two main components of adaptive immunity. Cell-mediated immunity involves T cells, specifically cytotoxic T cells (TC cells) and helper T cells (TH cells), which target and destroy intracellular pathogens, such as viruses inside host cells. T cells use T cell receptors (TCRs) to recognize specific antigens. On the other hand, humoral immunity involves B cells and antibodies. B cells use B cell receptors (BCRs) to recognize antigens and can differentiate into plasma cells that secrete antibodies. These antibodies target extracellular pathogens, such as bacteria in the bloodstream. Both systems work together to provide a comprehensive immune response.

What are primary and secondary lymphoid organs?

Primary lymphoid organs are where immature T and B lymphocytes develop into their naive forms. The thymus is where T cells develop, and the bone marrow is where B cells develop. Both T and B cells are initially produced in the bone marrow, but T cells migrate to the thymus to fully mature. Secondary lymphoid organs are where naive T and B lymphocytes become activated upon encountering antigens. These organs include lymph nodes, the spleen, and tonsils. Activation in these organs allows the lymphocytes to carry out their immune functions effectively.

How do T cells and B cells become activated?

T cells and B cells become activated when they encounter their specific antigens. For T cells, activation occurs through antigen-presenting cells (APCs) like dendritic cells, which present the antigen to the T cell receptors (TCRs) on naive T cells. This interaction, along with co-stimulatory signals, activates the T cells, allowing them to differentiate into effector and memory T cells. B cells become activated when their B cell receptors (BCRs) bind to their specific antigen. Helper T cells (TH cells) can further assist in B cell activation by providing additional signals. Activated B cells can then differentiate into plasma cells that secrete antibodies or memory B cells for long-term immunity.

What are the roles of cytotoxic T cells and helper T cells in adaptive immunity?

Cytotoxic T cells (TC cells) and helper T cells (TH cells) play crucial roles in adaptive immunity. Cytotoxic T cells are responsible for directly killing infected cells, particularly those harboring intracellular pathogens like viruses. They recognize antigens presented by MHC class I molecules on infected cells and induce apoptosis in these cells. Helper T cells, on the other hand, do not directly kill infected cells but play a supportive role. They recognize antigens presented by MHC class II molecules on antigen-presenting cells (APCs) and secrete cytokines that help activate other immune cells, including B cells and cytotoxic T cells, enhancing the overall immune response.

What is the significance of memory cells in adaptive immunity?

Memory cells are crucial for the long-term effectiveness of adaptive immunity. Both memory T cells and memory B cells are generated after an initial immune response to a specific antigen. These cells persist in the body for years, providing a rapid and robust response upon re-exposure to the same antigen. Memory T cells can quickly differentiate into effector T cells, while memory B cells can rapidly produce antibodies. This secondary immune response is typically faster and more effective than the primary response, often preventing reinfection or reducing the severity of the disease.