Chapter 21 - Section 21.2 - Study Guide - Assess Your Learning Outcomes - Page 844: 5

White blood cells (WBCs), also known as leukocytes, are key players in the immune system's defense against pathogens and illnesses. Different types of WBCs have distinct mechanisms to combat infections, and they often work together to mount an effective immune response. Here's a brief overview of the major types of WBCs and their mechanisms: 1. **Neutrophils:** - Neutrophils are the most abundant type of WBC and are typically the first to arrive at the site of infection. - They phagocytose (engulf and digest) pathogens, debris, and dead cells. This process involves releasing enzymes and reactive oxygen species (ROS) to destroy engulfed materials. - Neutrophils also release antimicrobial proteins called defensins, which create pores in the membranes of pathogens, leading to their destruction. 2. **Monocytes and Macrophages:** - Monocytes are precursor cells that circulate in the blood and can differentiate into macrophages when they migrate into tissues. - Macrophages are large phagocytic cells found in various tissues. - Macrophages engulf pathogens, dead cells, and debris. They also present antigens to T cells to initiate specific immune responses. - Macrophages secrete cytokines, chemical messengers that regulate immune responses and inflammation. 3. **Dendritic Cells:** - Dendritic cells are specialized antigen-presenting cells found in tissues that are in contact with the external environment, such as skin and mucous membranes. - They capture antigens from pathogens and present them to T cells, initiating adaptive immune responses. - Dendritic cells also secrete cytokines to regulate immune responses. 4. **Natural Killer (NK) Cells:** - NK cells are part of the innate immune system and are responsible for detecting and destroying virus-infected cells and cancer cells. - They release cytotoxic granules containing perforin and granzymes. Perforin forms pores in the target cell's membrane, allowing granzymes to enter and induce apoptosis (cell death). 5. **T Lymphocytes (T Cells):** - T cells play a central role in adaptive immunity. - Helper T cells (CD4+ T cells) coordinate immune responses by releasing cytokines. They assist B cells in antibody production and activate cytotoxic T cells. - Cytotoxic T cells (CD8+ T cells) directly kill infected or cancerous cells by releasing perforin and granzymes. 6. **B Lymphocytes (B Cells):** - B cells are responsible for antibody production in response to antigens. - Upon activation, B cells differentiate into plasma cells that secrete antibodies. Antibodies neutralize pathogens by binding to their surfaces. These WBCs, along with their associated chemical mediators such as cytokines, antibodies, enzymes, and antimicrobial peptides, work collaboratively to eliminate pathogens, regulate immune responses, and maintain overall health.

White blood cells (WBCs), also known as leukocytes, are key players in the immune system's defense against pathogens and illnesses. Different types of WBCs have distinct mechanisms to combat infections, and they often work together to mount an effective immune response. Here's a brief overview of the major types of WBCs and their mechanisms: 1. **Neutrophils:** - Neutrophils are the most abundant type of WBC and are typically the first to arrive at the site of infection. - They phagocytose (engulf and digest) pathogens, debris, and dead cells. This process involves releasing enzymes and reactive oxygen species (ROS) to destroy engulfed materials. - Neutrophils also release antimicrobial proteins called defensins, which create pores in the membranes of pathogens, leading to their destruction. 2. **Monocytes and Macrophages:** - Monocytes are precursor cells that circulate in the blood and can differentiate into macrophages when they migrate into tissues. - Macrophages are large phagocytic cells found in various tissues. - Macrophages engulf pathogens, dead cells, and debris. They also present antigens to T cells to initiate specific immune responses. - Macrophages secrete cytokines, chemical messengers that regulate immune responses and inflammation. 3. **Dendritic Cells:** - Dendritic cells are specialized antigen-presenting cells found in tissues that are in contact with the external environment, such as skin and mucous membranes. - They capture antigens from pathogens and present them to T cells, initiating adaptive immune responses. - Dendritic cells also secrete cytokines to regulate immune responses. 4. **Natural Killer (NK) Cells:** - NK cells are part of the innate immune system and are responsible for detecting and destroying virus-infected cells and cancer cells. - They release cytotoxic granules containing perforin and granzymes. Perforin forms pores in the target cell's membrane, allowing granzymes to enter and induce apoptosis (cell death). 5. **T Lymphocytes (T Cells):** - T cells play a central role in adaptive immunity. - Helper T cells (CD4+ T cells) coordinate immune responses by releasing cytokines. They assist B cells in antibody production and activate cytotoxic T cells. - Cytotoxic T cells (CD8+ T cells) directly kill infected or cancerous cells by releasing perforin and granzymes. 6. **B Lymphocytes (B Cells):** - B cells are responsible for antibody production in response to antigens. - Upon activation, B cells differentiate into plasma cells that secrete antibodies. Antibodies neutralize pathogens by binding to their surfaces. These WBCs, along with their associated chemical mediators such as cytokines, antibodies, enzymes, and antimicrobial peptides, work collaboratively to eliminate pathogens, regulate immune responses, and maintain overall health.