Chapter 21 - Section 21.1 - The Lymphatic System - Before You Go On - Page 816: 3

Natural Killer (NK) cells, T cells, and B cells are all types of immune cells that play important roles in the body's immune response. While they are part of the same immune system, they have distinct characteristics and functions. Here's an overview of what they have in common and how their functions differ: **What they have in common:** 1. **Origins:** All three cell types originate from stem cells in the bone marrow. 2. **Immune System:** They are all components of the adaptive immune system, which means they contribute to the body's defense against infections and foreign invaders. 3. **Specificity:** T cells and B cells have receptors that allow them to recognize specific antigens, which are molecules found on the surface of pathogens or other foreign substances. NK cells, on the other hand, have a more general mechanism of identifying cells that are abnormal or infected. **How their functions differ:** 1. **NK Cells (Natural Killer Cells):** - **Function:** NK cells are a type of cytotoxic lymphocyte. Their primary role is to identify and eliminate cells that are infected with viruses or have become cancerous. They detect changes in the surface molecules of these abnormal cells and trigger their destruction. - **Specificity:** NK cells do not require prior exposure to an antigen to become activated. They respond to signs of distress or changes in cell surface markers, making them an important part of the innate immune response. - **Immune Response:** NK cells are involved in the early stages of immune responses and play a crucial role in controlling viral infections and tumor growth. 2. **T Cells:** - **Function:** T cells are a diverse group of immune cells that help regulate and coordinate the immune response. They can be further categorized into helper T cells, cytotoxic T cells, and regulatory T cells. - **Helper T Cells:** These cells assist other immune cells by releasing signaling molecules (cytokines) that activate B cells, cytotoxic T cells, and macrophages. They are crucial for enhancing the immune response against pathogens. - **Cytotoxic T Cells:** Also known as CD8+ T cells, these cells directly kill infected or abnormal cells by releasing toxic molecules that induce cell death. - **Regulatory T Cells:** These cells help prevent excessive immune responses and maintain immune tolerance, which is important for avoiding autoimmune reactions. - **Specificity:** T cells recognize specific antigens through their T cell receptors (TCRs). They require the presentation of antigens by antigen-presenting cells (APCs) to become activated. 3. **B Cells:** - **Function:** B cells are responsible for producing antibodies, which are proteins that specifically target and neutralize antigens. B cells also play a role in presenting antigens to helper T cells and contributing to immune memory. - **Specificity:** B cells have surface receptors called B cell receptors (BCRs) that allow them to bind to specific antigens. When activated by binding to an antigen, B cells can differentiate into plasma cells that secrete antibodies. - **Immune Response:** B cells are key players in the adaptive immune response, particularly in the defense against extracellular pathogens and toxins. In summary, NK cells, T cells, and B cells are integral parts of the immune system with distinct functions and mechanisms of action. While they all contribute to immunity, they specialize in different aspects of immune defense, from detecting and eliminating infected or abnormal cells (NK cells) to coordinating and executing immune responses against specific pathogens (T cells) and producing antibodies to neutralize antigens (B cells).

Natural Killer (NK) cells, T cells, and B cells are all types of immune cells that play important roles in the body's immune response. While they are part of the same immune system, they have distinct characteristics and functions. Here's an overview of what they have in common and how their functions differ: **What they have in common:** 1. **Origins:** All three cell types originate from stem cells in the bone marrow. 2. **Immune System:** They are all components of the adaptive immune system, which means they contribute to the body's defense against infections and foreign invaders. 3. **Specificity:** T cells and B cells have receptors that allow them to recognize specific antigens, which are molecules found on the surface of pathogens or other foreign substances. NK cells, on the other hand, have a more general mechanism of identifying cells that are abnormal or infected. **How their functions differ:** 1. **NK Cells (Natural Killer Cells):** - **Function:** NK cells are a type of cytotoxic lymphocyte. Their primary role is to identify and eliminate cells that are infected with viruses or have become cancerous. They detect changes in the surface molecules of these abnormal cells and trigger their destruction. - **Specificity:** NK cells do not require prior exposure to an antigen to become activated. They respond to signs of distress or changes in cell surface markers, making them an important part of the innate immune response. - **Immune Response:** NK cells are involved in the early stages of immune responses and play a crucial role in controlling viral infections and tumor growth. 2. **T Cells:** - **Function:** T cells are a diverse group of immune cells that help regulate and coordinate the immune response. They can be further categorized into helper T cells, cytotoxic T cells, and regulatory T cells. - **Helper T Cells:** These cells assist other immune cells by releasing signaling molecules (cytokines) that activate B cells, cytotoxic T cells, and macrophages. They are crucial for enhancing the immune response against pathogens. - **Cytotoxic T Cells:** Also known as CD8+ T cells, these cells directly kill infected or abnormal cells by releasing toxic molecules that induce cell death. - **Regulatory T Cells:** These cells help prevent excessive immune responses and maintain immune tolerance, which is important for avoiding autoimmune reactions. - **Specificity:** T cells recognize specific antigens through their T cell receptors (TCRs). They require the presentation of antigens by antigen-presenting cells (APCs) to become activated. 3. **B Cells:** - **Function:** B cells are responsible for producing antibodies, which are proteins that specifically target and neutralize antigens. B cells also play a role in presenting antigens to helper T cells and contributing to immune memory. - **Specificity:** B cells have surface receptors called B cell receptors (BCRs) that allow them to bind to specific antigens. When activated by binding to an antigen, B cells can differentiate into plasma cells that secrete antibodies. - **Immune Response:** B cells are key players in the adaptive immune response, particularly in the defense against extracellular pathogens and toxins. In summary, NK cells, T cells, and B cells are integral parts of the immune system with distinct functions and mechanisms of action. While they all contribute to immunity, they specialize in different aspects of immune defense, from detecting and eliminating infected or abnormal cells (NK cells) to coordinating and executing immune responses against specific pathogens (T cells) and producing antibodies to neutralize antigens (B cells).