4.3 Innate vs Adaptive Immunity: Innate Immunity

Overview of Immunities

  • Innate Immunity: Immunity you are born with, also known as inborn immunity.

    • Characteristics:

    • Always present in the body

    • Rapid response

    • Non-specific

Components of Innate Immunity

First Line of Defense

  • Skin and Mucous Membranes:

    • Skin:

    • Composed of keratinocytes tightly packed, providing a barrier against foreign substances.

    • Continuous regeneration and shedding of skin cells clear bacteria from the surface.

    • Sweat Glands: Produce sweat that creates an acidic pH on the skin, hindering bacterial growth.

    • Dendritic Cells (Langerhans Cells):

    • Present in the epidermis, capture antigens and activate the adaptive immune system.

  • Mucous Membranes: Found in respiratory, nasal, and gastrointestinal tracts.

    • Mucus: Traps pathogens, dust, and particles due to its sticky consistency.

    • Cilia: Small hair-like structures push mucus with trapped particles to the throat for expulsion or swallowing.

  • Other First Line Defenses:

    • Urine: Acidic nature helps prevent bacterial growth in the urethra.

    • Gastric Juices: Highly acidic, prevents growth and breaks down pathogens in the stomach.

    • Lacrimal Apparatus: Produces tears with antimicrobial properties to flush away particles.

    • Saliva: Washes microbes from teeth and oral surfaces.

Second Line of Defense

  • If pathogens breach the first line, the second line includes:

    • Natural Killer Cells:

    • Type of lymphocyte (5-10% of lymphocytes) found in spleen, lymph nodes, and bone marrow.

    • Attack abnormal body cells displaying unusual plasma membrane proteins, releasing toxic granules to kill target cells.

    • Phagocytes: Cells capable of phagocytosis, including neutrophils and macrophages.

    • Neutrophils: First responders to sites of infection.

    • Macrophages: Can be wandering (mobile) or fixed (stationary), ingesting pathogens and cleaning cellular debris.

Phagocytosis Process

  • Phagocytosis consists of five phases:

    1. Chemotaxis: Chemical attraction of phagocytes to the site of infection.

    2. Adherence: Phagocyte adheres to the foreign particle.

    3. Ingestion: Plasma membrane extends pseudopods to engulf the microbe, creating a phagosome.

    4. Digestion: Phagosome fuses with lysosome, forming a phagolysosome where digestive enzymes break down ingested materials.

    5. Killing Phase: Enzymes destroy the pathogen; components can be expelled or presented on cell surface to activate adaptive immunity.

  • Inflammation: Innate response to tissue damage characterized by redness, heat, swelling, and pain.

    • Purpose: Dispose of microbes or foreign materials at the injury site.

    • Three Basic Activities:

    1. Vasodilation: Increased blood vessel permeability instigated by histamine release following injury.

    2. Emigration of Phagocytes: Phagocytes (e.g. neutrophils) migrate to the injury site to clean up.

    3. Chemotaxis and Microbial Attack: Signals attract additional phagocytes like monocytes, which transform into macrophages for further cleanup.

  • Fever: Elevated body temperature as an immune response that can enhance immune function and inhibit microbial growth.

    • Mechanism: Fever speeds up cellular reactions and effectively helps in the immune response.

    • Caution: Low-grade fevers are beneficial; however, high fevers require medical intervention.

  • Antimicrobial Proteins: Found in the body's fluids, they discourage microbial growth.

    • Interferons: Produced by infected cells, they signal neighboring cells to produce antiviral proteins, preventing viral replication.

    • Complement System: A group of proteins in plasma that enhance immune reactions, leading to the lysis of cells, promotion of phagocytosis, and inflammation.

Summary of Innate Immunity

  • Non-specific, rapid, and born-with defenses that act to maintain health by preventing foreign invasion.

Adaptive Immunity

  • Occurs when innate immunity fails or is overwhelmed.

  • Characteristics: Specificity and delayed response compared to innate immunity.

  • Important Note: Further exploration of adaptive immunity will follow in a subsequent video for better understanding of its components and functioning in comparison to innate immunity.