Innate Immunity Study Notes

Innate Immunity
  • Definition: The first line of defense against pathogens, characterized by a non-specific immune response.
  • Key Features:
    • Acts as a nonspecific resistance mechanism against all microbes and foreign materials.
    • Lacks immunological memory.
Components of Innate Immunity

  • Human Microbiota:

    • Plays a vital role in inhibiting pathogen growth by competing for resources and space.

  • Mucous Membranes:

    • Produce lysozyme, which breaks down bacterial cell walls and lactoferrin, which sequesters iron, inhibiting microbial growth.
    • Other physical barriers include skin, stomach acidity (pH 2), and mucus that traps pathogens.
Immune Cells

  • Types of Cells:

    • Granulocytes: Neutrophils, eosinophils, basophils, involved in rapid immune responses.
    • Monocytes: Differentiate into macrophages and dendritic cells, crucial for phagocytosis and antigen presentation.
    • Lymphocytes: Include T cells (thymus-derived) and B cells (bone marrow-derived) for adaptive immunity.

  • Phagocytosis:

    • The process of engulfing and destroying pathogens by immune cells (monocytes, macrophages, neutrophils).
    • Mechanisms: Opsonization enhances phagocytosis through antibody and complement binding which promotes efficiency.
Pathogen Recognition
  • Pattern Recognition Receptors (PRRs):
    • Toll-like Receptors (TLRs): Detect extracellular pathogen-associated molecular patterns (PAMPs).
    • Found on various immune cells, they initiate signaling that regulates immune responses and enhances phagocytosis.
    • NOD-like Receptors (NLRs): Recognize intracellular PAMPs and activate similar immune responses as TLRs.
Cytokines and Their Functions
  • Definition: Small signaling molecules released by cells that mediate immune responses.
  • Types:
    • Chemokines: Attract leukocytes to sites of infection.
    • Interleukins: Involved in cell growth and differentiation.
    • Tumor Necrosis Factor (TNF): Induces apoptosis and inflammation.
Complement System
  • Function: Consists of over 30 serum proteins that enhance the ability to clear pathogens from an organism.
  • Mechanisms: Facilitates opsonization, inflammation, and lysis of pathogens through various pathways: classical, lectin, and alternative.
  • Opsonization: Marks pathogens for destruction by phagocytes through complement proteins (e.g., C3b).
Antimicrobial Peptides
  • Cationic Peptides:
    • Classes:
    1. Linear peptides (e.g., cathelicidin) that disrupt microbial membranes.
    2. Defensins: Disulfide linked peptides found in body secretions that also kill microbes.
    3. Histatins: Present in saliva with antifungal activity.
Summary of Key Processes
  • Phagocytosis:
    • Recognition (opsonin-independent and dependent), ingestion, and destruction of pathogens inside phagolysosomes using reactive oxygen species (ROS).
  • Cytokine signaling:
    • Regulates inflammation, attracts immune cells, and promotes immune cell proliferation and differentiation.
    • Critical for the coordination between the innate and adaptive immune systems.
Importance of Non-Specific Immunity
  • Provides a rapid response to infections and maintains homeostasis by clearing dead cells and pathogens from the body.
  • Integral in supporting the more specific adaptive immune responses that follow.