NURS 311: Innate Immune System Video

Overview of the Immune System

  • Types of Immunity

    • Innate Immunity (Nonspecific Immunity)

    • Rapid response and first line of defense.

    • Present at all times, immediately activated upon invasion by foreign objects.

    • Non-selective; indiscriminately targets and kills foreign invaders.

    • Composed of physical barriers, chemical barriers, and cellular defenses.

    • Acquired Immunity (Adaptive Immunity)

    • Slow response, occurs after innate immunity has started.

    • Very selective; specifically targets and kills particular bacteria and viruses.

    • Two types of responses:

      • Humoral Responses (Antibody-mediated responses)

      • Cell-mediated Responses (Cytotoxic lymphocytes)

Analogy of Innate and Acquired Immunity

  • Castle Analogy:

    • The body is likened to a castle. Innate immunity serves to prevent invaders from breaching the castle walls, while acquired immunity is peeking out after the initial defenses are breached.

Components of Innate Immunity

  • Key Cells Involved:

    • Neutrophils

    • Eosinophils

    • Basophils

    • Monocytes

    • Lymphocytes (more related to acquired immunity)

  • Cellular Relative Abundance:

    • Remember the mnemonic: “Never Let Monkeys Eat Bananas” to order leukocyte abundance from most to least:

    • Neutrophils (most abundant)

    • Lymphocytes

    • Monocytes

    • Eosinophils

    • Basophils (least abundant)

Physical and Chemical Barriers in Innate Immunity

  • Lysozymes:

    • Found in tears and secretions, act as antibacterial agents (not to be confused with lysosomes).

    • Help kill bacteria on skin via secretions.

  • Skin:

    • Acts as a physical barrier with components that affect pH and contain normal flora preventing foreign invader survival.

  • Mucus and Cilia:

    • Mucus traps foreign particles, while cilia propel debris up the respiratory tract towards the mouth for expulsion (swallowing or spitting).

    • Swallowed particles enter a highly acidic stomach environment (pH 2), further aiding in pathogen destruction.

Inflammation

  • Definition:

    • A bodily response to tissue damage or microbial invasion; signs include swelling, redness, heat, and pain.

  • Goals of Inflammation:

    • Recruit phagocytes to the site of injury or infection.

    • Inactivate invaders and clear cellular debris.

    • Promote healing.

  • Involved Cells:

    • Macrophages: Start phagocytizing as soon as invaders enter a wound.

    • Mast Cells: Release histamine in response to injury or infection.

  • Histamine Effects:

    • Causes vasodilation and increased blood flow to the injured area, resulting in redness and warmth, while elevating plasma proteins important for healing.

    • Increases capillary permeability leading to edema (fluid accumulation) and potential pain from excess fluid.

Phagocytosis

  • Definition: A specific form of endocytosis performed by phagocytes to eliminate invaders.

  • Steps in Phagocytosis:

    1. Recognition and attachment of the invader.

    2. Engulfment of the invader producing a phagosome.

    3. Fusion of phagosome with lysosome.

    4. Destruction of the invader.

  • Opsonins:

    • Substances that coat pathogens to enhance phagocytosis by marking them for engulfment.

Interferon

  • Function:

    • Interferes with viral replication inside host cells.

    • When a virus infects a cell, the infected cell releases interferon into the extracellular space, which then serves to alert neighboring healthy cells.

  • Mechanism of Action:

    • Healthy cells produce inactive enzymes that become activated upon infection, leading to inhibition of viral RNA and protein synthesis.

Natural Killer Cells

  • Function:

    • Similar to lymphocytes, involved in the innate immune response.

    • Target and kill cancer cells and virally infected cells by releasing perforins that create pores in the membranes of the target cells, resulting in lysis.

Complement System

  • Activation:

    • Proteins that recognize carbohydrates on bacterial cells, leading to a cascade of events forming a Membrane Attack Complex (MAC).

    • The MAC forms pores in bacterial membranes, leading to cell lysis.

Limitations and Transition to Acquired Immunity

  • Limitations of Innate Immunity:

    • Cannot specifically target particular bacterial species; response is short-term and non-specific.

    • Necessitates acquired immunity for a more robust and specialized defense mechanism.

  • The next discussion will focus on characteristics of B and T cells in adaptive immunity.