Chapter 21 - Section 21.1 - The Lymphatic System - Before You Go On - Page 816: 4

Lymphatic tissues are a crucial part of the immune system and play a significant role in defending the body against infections and diseases. There are several major cell types found within lymphatic tissues, each with specific functions. Here are five major cell types of lymphatic tissues and their functions: 1. **B Cells:** - **Function:** B cells are lymphocytes that play a central role in the adaptive immune response. They are responsible for producing antibodies, also known as immunoglobulins, which are proteins that can recognize and bind to specific antigens (foreign substances or pathogens). When activated by an antigen, B cells can differentiate into plasma cells, which produce large quantities of antibodies that target and neutralize the antigen. B cells are particularly important in defending against infections caused by bacteria, viruses, and other extracellular pathogens. 2. **T Cells:** - **Function:** T cells are another type of lymphocyte that plays a critical role in the adaptive immune response. There are several subtypes of T cells, including helper T cells, cytotoxic T cells, and regulatory T cells, each with distinct functions: - Helper T Cells (CD4+ T cells): These cells assist in coordinating the immune response by releasing cytokines that activate other immune cells, including B cells, cytotoxic T cells, and macrophages. They also help regulate immune reactions and promote immune memory. - Cytotoxic T Cells (CD8+ T cells): Cytotoxic T cells are responsible for directly killing infected or abnormal cells. They recognize cells displaying antigens on their surfaces and induce cell death through the release of cytotoxic molecules. - Regulatory T Cells: These cells play a role in immune tolerance by suppressing excessive immune responses, helping to prevent autoimmune reactions and maintaining immune equilibrium. 3. **Macrophages:** - **Function:** Macrophages are phagocytic cells that engulf and digest foreign particles, pathogens, and cellular debris. They are essential components of the innate immune response, serving as the body's "first line of defense." Macrophages also play a role in presenting antigens to T cells, which helps activate specific immune responses. 4. **Dendritic Cells:** - **Function:** Dendritic cells are professional antigen-presenting cells that capture, process, and present antigens to T cells. They play a pivotal role in initiating adaptive immune responses. Dendritic cells are often found at sites where the body is likely to encounter pathogens, such as skin, mucosal surfaces, and lymphoid tissues. 5. **Natural Killer (NK) Cells:** - **Function:** NK cells are lymphocytes of the innate immune system that recognize and eliminate virus-infected cells and cancerous cells. Unlike T cells, NK cells do not require prior exposure to an antigen for activation. They identify abnormal cells based on changes in cell surface markers and induce cell death to prevent the spread of infections and inhibit tumor growth. These five major cell types of lymphatic tissues work together to provide a comprehensive immune response, involving both innate and adaptive immunity. By coordinating their functions, these cells help protect the body from a wide range of pathogens and maintain overall health and immune homeostasis.

Lymphatic tissues are a crucial part of the immune system and play a significant role in defending the body against infections and diseases. There are several major cell types found within lymphatic tissues, each with specific functions. Here are five major cell types of lymphatic tissues and their functions: 1. **B Cells:** - **Function:** B cells are lymphocytes that play a central role in the adaptive immune response. They are responsible for producing antibodies, also known as immunoglobulins, which are proteins that can recognize and bind to specific antigens (foreign substances or pathogens). When activated by an antigen, B cells can differentiate into plasma cells, which produce large quantities of antibodies that target and neutralize the antigen. B cells are particularly important in defending against infections caused by bacteria, viruses, and other extracellular pathogens. 2. **T Cells:** - **Function:** T cells are another type of lymphocyte that plays a critical role in the adaptive immune response. There are several subtypes of T cells, including helper T cells, cytotoxic T cells, and regulatory T cells, each with distinct functions: - Helper T Cells (CD4+ T cells): These cells assist in coordinating the immune response by releasing cytokines that activate other immune cells, including B cells, cytotoxic T cells, and macrophages. They also help regulate immune reactions and promote immune memory. - Cytotoxic T Cells (CD8+ T cells): Cytotoxic T cells are responsible for directly killing infected or abnormal cells. They recognize cells displaying antigens on their surfaces and induce cell death through the release of cytotoxic molecules. - Regulatory T Cells: These cells play a role in immune tolerance by suppressing excessive immune responses, helping to prevent autoimmune reactions and maintaining immune equilibrium. 3. **Macrophages:** - **Function:** Macrophages are phagocytic cells that engulf and digest foreign particles, pathogens, and cellular debris. They are essential components of the innate immune response, serving as the body's "first line of defense." Macrophages also play a role in presenting antigens to T cells, which helps activate specific immune responses. 4. **Dendritic Cells:** - **Function:** Dendritic cells are professional antigen-presenting cells that capture, process, and present antigens to T cells. They play a pivotal role in initiating adaptive immune responses. Dendritic cells are often found at sites where the body is likely to encounter pathogens, such as skin, mucosal surfaces, and lymphoid tissues. 5. **Natural Killer (NK) Cells:** - **Function:** NK cells are lymphocytes of the innate immune system that recognize and eliminate virus-infected cells and cancerous cells. Unlike T cells, NK cells do not require prior exposure to an antigen for activation. They identify abnormal cells based on changes in cell surface markers and induce cell death to prevent the spread of infections and inhibit tumor growth. These five major cell types of lymphatic tissues work together to provide a comprehensive immune response, involving both innate and adaptive immunity. By coordinating their functions, these cells help protect the body from a wide range of pathogens and maintain overall health and immune homeostasis.