Chapter 21 - Section 21.4 - Study Guide - Assess Your Learning Outcomes - Page 845: 5

Activated T cells play a crucial role in coordinating the immune response by interacting with and stimulating various other immune cells, such as neutrophils, natural killer (NK) cells, and macrophages. This coordination enhances the overall effectiveness of the immune system's response to infections and other challenges. Here's how activated T cells stimulate these immune cells: **1. Stimulation of Neutrophils:** Neutrophils are a type of white blood cell that plays a key role in the early stages of the immune response, particularly against bacterial infections. Activated T cells, specifically helper T cells (CD4+ T cells), can stimulate neutrophils through the release of cytokines. - **Cytokine Release**: Activated helper T cells release cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-γ). - **Neutrophil Activation**: These cytokines stimulate neutrophils, enhancing their ability to migrate to the site of infection, phagocytose pathogens, and produce reactive oxygen species (ROS) to kill engulfed microorganisms. - **Inflammation Regulation**: Activated T cells can modulate the inflammation process by promoting the recruitment and activation of neutrophils to the site of infection while also preventing excessive inflammation. **2. Stimulation of Natural Killer (NK) Cells:** NK cells are specialized immune cells that play a role in innate immunity by recognizing and eliminating infected or abnormal cells, including those that have downregulated MHC molecules. Activated T cells, particularly certain subsets of helper T cells, can influence NK cell activity. - **Interferon-Gamma (IFN-γ) Release**: Activated helper T cells, such as Th1 cells, release IFN-γ, which enhances NK cell activity. - **Enhanced Cytotoxicity**: IFN-γ increases the cytotoxicity of NK cells, enhancing their ability to target and kill infected or stressed cells. - **Antiviral Response**: NK cells activated by T cell-derived cytokines can target virally infected cells that might evade other immune mechanisms due to reduced MHC expression. **3. Stimulation of Macrophages:** Macrophages are phagocytic immune cells that engulf and destroy pathogens, clear debris, and play a role in initiating and regulating immune responses. Activated T cells, particularly Th1 cells, can stimulate macrophages to enhance their antimicrobial functions. - **Cytokine Release**: Activated Th1 cells release cytokines such as IFN-γ and tumor necrosis factor-alpha (TNF-α). - **Macrophage Activation**: These cytokines activate macrophages, increasing their phagocytic capacity, enhancing antigen presentation, and promoting the production of antimicrobial molecules. - **Granuloma Formation**: In chronic infections, activated T cells stimulate macrophages to form granulomas, which encapsulate persistent pathogens and prevent their spread. In summary, activated T cells, particularly helper T cells (such as Th1 cells), release specific cytokines that stimulate neutrophils, NK cells, and macrophages. These interactions optimize the immune response by coordinating the actions of different immune cell types to efficiently target and eliminate pathogens and infected cells.

Activated T cells play a crucial role in coordinating the immune response by interacting with and stimulating various other immune cells, such as neutrophils, natural killer (NK) cells, and macrophages. This coordination enhances the overall effectiveness of the immune system's response to infections and other challenges. Here's how activated T cells stimulate these immune cells: **1. Stimulation of Neutrophils:** Neutrophils are a type of white blood cell that plays a key role in the early stages of the immune response, particularly against bacterial infections. Activated T cells, specifically helper T cells (CD4+ T cells), can stimulate neutrophils through the release of cytokines. - **Cytokine Release**: Activated helper T cells release cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-γ). - **Neutrophil Activation**: These cytokines stimulate neutrophils, enhancing their ability to migrate to the site of infection, phagocytose pathogens, and produce reactive oxygen species (ROS) to kill engulfed microorganisms. - **Inflammation Regulation**: Activated T cells can modulate the inflammation process by promoting the recruitment and activation of neutrophils to the site of infection while also preventing excessive inflammation. **2. Stimulation of Natural Killer (NK) Cells:** NK cells are specialized immune cells that play a role in innate immunity by recognizing and eliminating infected or abnormal cells, including those that have downregulated MHC molecules. Activated T cells, particularly certain subsets of helper T cells, can influence NK cell activity. - **Interferon-Gamma (IFN-γ) Release**: Activated helper T cells, such as Th1 cells, release IFN-γ, which enhances NK cell activity. - **Enhanced Cytotoxicity**: IFN-γ increases the cytotoxicity of NK cells, enhancing their ability to target and kill infected or stressed cells. - **Antiviral Response**: NK cells activated by T cell-derived cytokines can target virally infected cells that might evade other immune mechanisms due to reduced MHC expression. **3. Stimulation of Macrophages:** Macrophages are phagocytic immune cells that engulf and destroy pathogens, clear debris, and play a role in initiating and regulating immune responses. Activated T cells, particularly Th1 cells, can stimulate macrophages to enhance their antimicrobial functions. - **Cytokine Release**: Activated Th1 cells release cytokines such as IFN-γ and tumor necrosis factor-alpha (TNF-α). - **Macrophage Activation**: These cytokines activate macrophages, increasing their phagocytic capacity, enhancing antigen presentation, and promoting the production of antimicrobial molecules. - **Granuloma Formation**: In chronic infections, activated T cells stimulate macrophages to form granulomas, which encapsulate persistent pathogens and prevent their spread. In summary, activated T cells, particularly helper T cells (such as Th1 cells), release specific cytokines that stimulate neutrophils, NK cells, and macrophages. These interactions optimize the immune response by coordinating the actions of different immune cell types to efficiently target and eliminate pathogens and infected cells.