White Blood Cell Types and Functions

White Blood Cell Types and Functions

• Neutrophils: Phagocytic cells, crucial in the initial response to infection, engulf and destroy pathogens.
• Lymphocytes: Include B cells (produce antibodies), T cells (cell-mediated immunity), and natural killer (NK) cells (attack abnormal cells).
• Monocytes: Become macrophages, large phagocytic cells that engulf pathogens, cellular debris, and foreign material. They are important for antigen presentation.
• Eosinophils: Combat parasitic infections, involved in allergic reactions.
• Basophils: Release histamine, contributing to allergic reactions and inflammation.

Phagocytosis Steps

• Recognition and Attachment: Phagocytes recognize pathogens (via pattern recognition receptors or opsonization). They adhere to the pathogen's surface.
• Engulfment: The phagocyte membrane extends around the pathogen, forming a phagosome (a vesicle).
• Phagosome Formation: The phagosome containing the pathogen is fully enclosed.
• Phagolysosome Formation: The phagosome fuses with lysosomes, which contain digestive enzymes.
• Digestion: Enzymes in the lysosome break down the pathogen.
• Elimination: Undigested material is released from the phagocyte.

Chemotaxis

• Chemotaxis is the movement of cells along a chemical gradient. It's crucial for phagocytes to reach infection sites.
• Chemicals released by pathogens or damaged cells attract phagocytic cells, guiding their movement.

Complement System and Immunity

• The complement system is a group of proteins in the blood that enhances the immune response.
• Activation of the complement system results in:
  • Opsonization (coating pathogens for easier phagocytosis).
  • Inflammation (enhancing inflammation and attracting immune cells).
  • Cytolysis (forming pores in pathogen membranes, destroying pathogens).
• Complement activation is critical for destroying pathogens and initiating the inflammatory response, facilitating immune responses.

Lines of Defense

• First Line: Physical and chemical barriers (e.g., skin, mucous membranes, enzymes, stomach acid).
• Second Line: Innate (non-specific) immune responses, including phagocytosis, inflammation, fever, and complement system.
• Third Line: Adaptive (specific) immunity, involving lymphocytes, antibodies, and memory cells.

Inflammation

• Molecules Involved: Histamine, cytokines (e.g., TNF-α, IL-1, IL-6), prostaglandins, leukotrienes.
• These molecules cause increased blood flow, vascular permeability, pain, swelling, heat, and redness—the hallmarks of inflammation.

Inflammation Symptoms

• Inflammation symptoms arise from the body's reaction to the molecules released during the response:
  • Redness from increased blood flow to the area.
  • Swelling from fluid leaking into tissues.
  • Pain from the release of chemical mediators.
  • Heat from increased blood flow.

Pathogen-Associated Molecular Patterns (PAMPs)

• PAMPs are molecules found on various pathogens but often absent in host cells.
• They are important because they are recognized by pattern recognition receptors (PRRs) on phagocytes and other immune cells.
• Recognition of PAMPs triggers immune responses.
• Examples of PAMPs include lipopolysaccharide (LPS) from Gram-negative bacteria, peptidoglycans from bacterial cell walls, bacterial flagellin, and viral nucleic acids.

Monocyte

• Monocytes are a type of white blood cell that differentiates into macrophages. They are important phagocytic cells.

Opsonization

• Opsonization is the coating of a pathogen with molecules (like antibodies or complement proteins).
• This enhances phagocytosis by marking the pathogen for recognition and engulfment by phagocytes.

Cytokines and Fever

• Pro-inflammatory cytokines (like TNF-α, IL-1) induce fever by acting on the hypothalamus in the brain to raise body temperature.
• Fever can help the body fight infection by increasing metabolic rate, enhancing immune responses, and inhibiting microbial growth.

Leukocytes

• Leukocytes are white blood cells. There are various types as listed above. Each plays a specific function in the immune response.

This quiz covers the various types of white blood cells and their specific functions in the immune response. You'll learn about neutrophils, lymphocytes, monocytes, eosinophils, and basophils, along with the steps of phagocytosis. Test your knowledge on how these cells work together to protect the body against infections.