Lecture 31 - Immune Cells in the Blood

• Blood


  Composed of plasma and cells
• Plasma


  • Fluid component of blood
  • Contains proteins, including antibodies produced by B cells
• Formed elements


  • Cellular component of blood
  • Includes red blood cells, platelets, and white blood cells
• White blood cells


  • Also called leukocytes
  • Do not have any color when viewed under a microscope
  • Nucleus stains purple, granules stain red when stained
• Blood cell lineages


  Divide into myeloid and lymphoid lineages
• Myeloid lineage


  • Red blood cells
  • Granulocytes (with granules)
  • Monocytes
  • Dendritic cells
  • Platelets
• Lymphoid lineage


  • B lymphocytes
  • T lymphocytes
• Granulocytes


  • White blood cells characterized by the presence of granules in their cytoplasm
  • Granules contain enzymes and antimicrobial proteins
  • Play important roles in the immune response
• Neutrophils


  • 75% of all leukocytes
  • Highly phagocytic "eat and kill"
  • Numbers increase during infection
• Mast cells


  • Line mucosal surfaces (not found in blood)
  • Release granules that attract white blood cells to areas of tissue damage
• Monocytes


  • Present in blood with low phagocytosis
  • Develop into macrophages in tissues with high phagocytosis
• Macrophages


  • Present in lungs, spleen, liver, brain, etc.
  • Can be resident (not moving) or migratory
  • Perform phagocytosis, release chemical messengers, and present information about pathogens to T cells
• Dendritic cells


  • Found in low numbers in blood and all tissues in contact with the environment
  • Phagocytic
  • Most important cell type to help trigger adaptive immune responses and prime T cell responses
• How immune cells move around the body

  1. Carried in blood and lymph

  2. Can leave blood to enter tissues

  3. Lymph in tissues collects into lymphatic vessels and drains into lymph nodes
• Pattern recognition receptors (PRRs)

  • Found on the cell surface
  • Bind to pattern-associated molecular patterns (PAMPs)
  • Trigger cellular responses, such as increased gene transcription and production of chemical messengers
• PAMPs


  Common building blocks of pathogens, such as viral nucleic acids and bacterial cell wall components
• Fever/Pyrexia


  • Abnormally high temperature above 37°C
  • Caused by pyrogens released by immune cells, such as interleukin-1
  • Helps inhibit bacterial replication and promote immune system effectiveness
• Lymphoid Lineage


  Comprises B and T lymphocytes, crucial for adaptive immunity. They produce molecules that aid immune responses.
• Phagocytic cells


  • Neutrophils
  • Monocytes (which differentiate into macrophages)
  • Dendritic cells
• Phagocytic cells


  • Engulf and destroy pathogens
• Neutrophils


  • Highly phagocytic and increase during infections
• Macrophages


  • Play vital roles in tissue phagocytosis and antigen presentation to T cells
• How innate cells recognize pathogens

  1. Pattern recognition receptors (PRRs) bind to pattern-associated molecular patterns (PAMPs)

  2. PRRs are located on cell surfaces (e.g., toll-like receptors) and inside cells (e.g., nucleic acid sensors)

  3. PAMPs include bacterial cell wall components (e.g., lipopolysaccharide) and viral nucleic acids

  4. Binding of PRRs to PAMPs triggers cellular responses, such as increased gene transcription and the production of chemical messengers, aiding in the immune response
• How fever is induced

  1. Release of pyrogens, such as interleukin-1 (IL-1), by immune cells, particularly phagocytes, upon encountering pathogens

  2. Pyrogens stimulate the hypothalamus in the brain to raise the body's temperature set point, leading to fever

  3. Fever inhibits bacterial replication and enhances immune function, promoting the efficacy of the immune response

  4. Once the pyrogen levels decrease, the hypothalamus resets to normal temperature, and the fever subsides