phys

Introduction

  • Discussion of the dual immune system: innate vs adaptive immune systems.

  • Focus on the characteristics and functions of innate immunity which is nonspecific, compared to the adaptive immune system which evolves.

Innate Immunity

  • Characteristics:

    • Always ready and activated in a consistent manner; responses are uniform.

    • Does not change with repeated exposure; no gradation of response (no "strong" vs. "weak").

  • Components of Innate Immunity:

    • First line of defense includes physical barriers like skin and mucous membranes.

    • Skin:

    • Composed of multiple layers (30+ layers) with the outermost layers being dead cells.

    • Prevents damage from pathogens unless breached to access the bloodstream.

    • Mucous Membranes:

    • Stratified squamous epithelium, providing protection similarly to the skin.

    • Secretions:

    • Mucus traps pathogens.

    • Tears and saliva contain enzymes to kill bacteria.

    • Skin has a specific pH that is inhospitable to pathogens; stomach acid serves a similar role.

  • Second line of defense includes cellular responses:

    • Phagocytes (engulfing cells):

    • Neutrophils: Leave blood to migrate into tissues to engulf pathogens.

    • Monocytes: Known as macrophages once they enter tissues; can consume more pathogens compared to neutrophils.

    • Eosinophils: Play a role in combating parasites and are more specific to larger pathogens which cannot be engulfed entirely.

Phagocytosis Process

  • Mechanism of Phagocytosis:

    • Phagocyte identifies and surrounds a foreign pathogen.

    • Membrane invaginates to engulf the pathogen, creating a vesicle.

    • Vesicle fuses with lysosomes that contain digestive enzymes to break down the pathogen:

    • Digests carbohydrates, proteins, lipids, etc.

    • Remnants of the pathogen are expelled from the cell.

  • Efficiency of Phagocytes:

    • Neutrophils: Can consume about 10 bacterial cells before die-off occurs.

    • Macrophages: Can consume approximately 100 cells, lasting longer in the immune response.

Eosinophils and Their Role

  • Eosinophils are implicated in allergic responses and in combating parasitic infections (e.g., worms).

  • Mechanism of action: Align themselves to the exterior of a large pathogen and release lysosomal enzymes to damage the target directly, as internally engulfing and digesting is impractical due to size constraints.

Interferons and Their Function

  • Interferons:

    • A class of cytokines crucial in managing viral infections.

    • Mechanism: Infected cells secrete interferons to signal nearby cells, creating a barrier that prevents further infection.

    • Interferons enhance the activity of macrophages, cytotoxic T cells, and natural killer cells, promoting a strong immune response against virus-infected cells.

The Complement System

  • The Complement System Overview:

    • Series of proteins produced by the liver in inactive forms, activated in response to infections.

  • Activation Pathways:

    • Classical Pathway: Triggered by antibodies binding to antigens.

    • Lectin Pathway: Triggered by the recognition of mannose on pathogen surfaces.

    • Alternative Pathway: Triggered by surface components of pathogens.

  • Outcomes:

    • Inflammation: Increases immune response at the infection site.

    • Opsonization: Marking pathogens for easier recognition and ingestion by phagocytes.

    • Membrane Attack Complex (MAC): Formation of pores in pathogen membranes, leading to cell lysis.

Fever as a Response

  • Fever:

    • A nonspecific response to infection that can hinder pathogen survival.

    • Mechanism: Released pyrogens from infected cells raise set-point temperature in the hypothalamus, causing fever.

    • Important temperatures:

    • Fevers help hinder bacterial growth and activity; can become dangerous if excessively high (above 106°F-109°F).

Natural Killer Cells

  • Natural Killer Cells:

    • Part of the innate immune system, they identify and destroy virus-infected and cancerous cells.

    • Use perforin to punch holes in targeted cells, leading to cell lysis.

Inflammation

  • Inflammation: Local barriers to infections, essential in recovery and repair processes.

    • Symptoms include redness, swelling, heat, and pain resulting from increased blood flow and fluid leakage at the infection site.

    • Essential in the repair and recovery process; necessary for normal immune function, but excessive or chronic inflammation can lead to tissue damage.