Ch. 12: Host Defense Phagocytic White Blood Cells, Inflammation, and the Immune Response

Phagocytic White Blood Cells

  • Types of Phagocytic White Blood Cells:

    • Neutrophils

    • Monocytes/Macrophages

  • Function:

    • These cells engulf and eliminate invaders, including:

    • Bacteria

    • Viruses

    • Dead cells (including self-cells)

    • Contribute to the formation of pus.

    • The term "white blood cells" originates from the color of pus, which is composed largely of these cells.

Neutrophils and Monocytes

  • Neutrophils:

    • First responders to sites of infection

  • Monocytes:

    • When in circulation, these cells transform into macrophages once they exit the bloodstream and enter tissues.

    • Macrophages can further differentiate into dendritic cells depending on location and function.

  • Analogies for Understanding:

    • Hematopoietic Stem Cells:

    • Pluripotent cells can be seen as teenagers without specific career paths.

    • Once they mature into different types of white blood cells, they symbolize individuals with specific jobs.

    • Transitioning from monocyte to macrophage/dendritic cell represents moving to a new career.

The Phagocytic Process

  • White blood cells perform the following duties:

    • Search and destroy:

    • They move around tissues looking for pathogens and debris.

    • Engulfing Process:

    • Chemotaxis: Cells are guided to targets through chemical signals.

    • Engulfment:

      • The invader is enveloped in a structure called the phagosome, which contains digestive enzymes for breakdown.

    • After digestion, undigested materials are expelled from the cell.

Inflammation

  • Definition:

    • Inflammation is a physiological response to traumatic events, including infections or physical damage.

  • Cardinal Signs of Inflammation:

    • In English:

    1. Redness

    2. Warmth

    3. Swelling

    4. Pain

    • In Latin:

    1. Rubor

    2. Calor

    3. Tumor

    4. Dolor

  • Mechanisms:

    • Increased blood flow due to vasodilation causes redness and warmth.

    • Fluid leaks from blood vessels into tissues, causing swelling (edema).

    • Swelling puts pressure on nerves, causing pain.

  • Goals of Inflammation:

    • Attract immune cells to the site of injury to repair damage and attack invading microbes.

  • Negative Aspects of Inflammation:

    • Excessive inflammation can exacerbate tissue damage and lead to complications, similar to how excessive mucus impairs breathing.

    • Anti-inflammatory Treatments:

    • Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or prescription anti-inflammatories may be necessary to manage excessive inflammation.

Steps of the Inflammatory Process

  1. Initial Injury:

    • Tissue damage begins the inflammatory response.

  2. Vascular Reactions:

    • Increased permeability of blood vessels; leakage leads to edema.

  3. Immune Cell Mobilization:

    • White blood cells migrate from circulation into injured tissues through a process called diapedesis, primarily involving monocytes transitioning into macrophages.

  4. Resolution:

    • Repair of tissue occurs, potentially resulting in scar formation.

Diapedesis and Edema

  • Diapedesis:

    • Monocytes leave circulation by squeezing through capillary walls into injured tissue, where they mature into macrophages.

  • Edema:

    • Results from leaky blood vessels, facilitating fluid migration into tissues.

    • Benefits include:

    • Dilution of toxins

    • Prevention of pathogen spread

    • Assistance in phagocytosis

  • Pus Formation:

    • Composed of cells, liquefied cellular debris, and bacteria (mainly from pyogenic microorganisms such as Staphylococcus, Streptococcus, and Neisseria).

Fever

  • Definition:

    • Fever is a systemic increase in body temperature, indicating an ongoing immune response.

  • Mechanism:

    • Resetting of the hypothalamus promotes a higher temperature to create an inhospitable environment for pathogens.

  • Temperature Control:

    • Low-grade fevers (e.g., 100-101°F) may not require treatment unless the patient feels unwell.

    • High fevers (e.g., above 103°F) can lead to dangerous consequences such as brain damage due to protein denaturation.

  • Treatment:

    • High fevers require urgent attention, including cooling methods like ice baths or cooling blankets.

  • Pyrogens:

    • Substances initiating fever can be:

    • Exogenous Pyrogens: External agents from pathogens.

    • Endogenous Pyrogens: Produced internally by white blood cells during immune responses.

Antimicrobial Products

  • Definition:

    • Antimicrobial products are host-generated substances that combat microbial infections.

  • Types:

    • Interferon:

    • Small proteins that inhibit viral replication and have implications in cancer.

    • Complement System:

    • A series of approximately 30 proteins that work in a cascade reaction to destroy bacteria and enhance immune functioning.

    • Acts through lysing pathogens.

    • Antimicrobial Peptides:

    • Short proteins (12 to 50 amino acids) that disrupt microbial membranes, essentially acting as pore-forming agents against pathogens.

  • Characteristics:

    • Antimicrobial products are species-specific but not pathogen-specific.

    • Examples include human, cow, and dog versions of interferon, but they act against a broad spectrum of invaders.

Conclusion

  • The session concludes with a brief overview of the immune system, emphasizing that after break, the focus will shift to specific immunity and vaccinations.