Study Notes on the Innate Immune Response

Overview of the Lymphatic and Immune System

  • This recording focuses on the innate immune response, a vital part of the immune system.

Phases of Immune Responses

  • Three Phases based on timing:

    • Barrier Defences

    • Innate Immune Response

    • Adaptive Immune Response

Barrier Defenses

  • Definition: Initial physical barriers preventing pathogen entry or flushing them out.

  • Examples of Barrier Defenses:

    • Skin: Acts as a physical barrier.

    • Saliva: Contains enzymes that destroy bacteria—rich in lysozyme.

    • Tears: Contribute to barrier defense.

    • Gastric Juices: Highly acidic, killing most pathogens.

  • Role: Prevent pathogenic invasion before they attach to body tissues.

Immune Responses After Pathogen Invasion

  • When pathogens breach barriers, the innate immune response and adaptive immune response are activated.

Immune Cells and Their Origin

  • Origin: All immune cells arise from hematopoietic stem cells in bone marrow.

  • Types of Blood Cells:

    • Red Blood Cells

    • White Blood Cells (Leukocytes)

    • Functionally categorized into:

      • Phagocytic Cells: e.g., Macrophages, Neutrophils (responsible for ingesting microbes via phagocytosis).

      • Lymphocytes: Coordinate adaptive immunity.

      • Granule-Containing Cells: Target parasites and intracellular pathogens.

Lymphocytes

B Cells

  • Function: Produce antibodies.

  • Maturation: Occur in red bone marrow and circulate in blood and lymph.

  • Role in Adaptive Immunity: B cells differentiate into plasma cells upon activation.

T Cells

  • Maturation: Occur in the thymus gland.

  • Functions: Do not produce antibodies; instead:

    • Communicate with other immune cells via soluble factors.

    • Destroy infected cells directly.

Plasma Cells

  • Definition: Differentiated B cells that secrete antibodies.

  • Characteristics: Have abundant rough endoplasmic reticulum (RER) for protein synthesis.

Natural Killer Cells (NK Cells)

  • Function: Part of innate immune response, execute apoptosis (programmed cell death) on infected or cancer cells.

Activation of Innate Immune Response

  • Characteristics: Rapid but non-specific, protects against all antigens.

  • Recognizes features of pathogens absent in healthy cells.

Phagocytosis

  1. Detection of foreign particles.

  2. Ingestion by macrophages or neutrophils (internalization).

  3. Formation of a phagosome (bubble with pathogens).

  4. Fusion with lysosomes that release digestive enzymes (lysozymes) to degrade pathogens.

  5. Disposal of harmless bits via lymphatic and circulatory systems.

Inflammatory Response

  • Definition: Body's immune reaction to injury or irritant (e.g., pathogens, foreign objects).

  • Types:

    • Acute Inflammation: Immediate, short-term response.

    • Chronic Inflammation: Long-term response lasting months or years (e.g., autoimmune disorders).

  • Steps:

    1. Mast Cells detect injury, release histamine.

    2. Histamine causes vasodilation and increases permeability of blood vessels.

    3. Influx of blood plasma and phagocytic cells to the injury site leads to four signs of inflammation:

    • Redness

    • Swelling

    • Heat

    • Pain

Complement System

  • Definition: Group of proteins that enhance both innate and adaptive immunity.

  • Location: Synthesized in the liver and found in blood plasma as inactive precursors.

  • Functions:

    • Opsonization: Labels pathogens for easy recognition by immune cells.

    • Pokes holes in pathogen membranes, leading to lysis (disintegration of the pathogen).

Pathways of the Complement Cascade

  • Classical Pathway: Requires antibodies (part of adaptive immune response).

  • Alternative Pathway: Does not require antibodies to activate.

Cytokines and Chemokines

  • Cytokines: Small proteins guiding immune responses (e.g., interferons, interleukins).

    • Functions via receptors; do not cross cell membranes.

    • Induce specific functions in immune cells.

  • Chemokines: Stimulate immune cell migration over longer distances.

Recognition of Pathogens

  • Pathogen Recognition: Conducted via pathogen-associated molecular patterns (PAMPs) interacting with pattern recognition receptors (PRRs) on immune cells.

  • Function: Initiates phagocytosis or apoptosis in response to pathogens.

Conclusion

  • The innate immune response is crucial for the initial defense against infections.

  • Next module will address the adaptive immunity.