Understanding Innate Immunity: Body's First Defenses

Immunity Fundamentals

The ability to ward off disease through the body's defenses is called immunity.

Understanding Immunity Concepts

• Susceptibility

  Lack of resistance to a disease.

• Immunity Defined

  The ability to ward off disease.

• Genetic Resistance

  The inability of a pathogen to cause disease.

  • Genetic variation in an individual results in a lack of receptors for pathogen binding or other structures required by the pathogen.

• Innate Immunity

  Defenses against any pathogen.

  • Present at birth.
  • Comprises all body defenses that protect the body against any kind of pathogen.

• Adaptive Immunity

  Immunity or resistance to a specific pathogen.

  • Defenses (antibodies) against specific microorganisms.

Innate Immunity Activation

Innate immunity is activated by protein receptors found in the plasma membranes of defensive cells.

• Pattern Recognition Receptors (PRRs)

  White Blood Cells (WBCs) have PRRs on their surface.

  • Toll-like receptors (TLRs) in the plasma membranes of macrophages and dendritic cells bind to invading microbes.

• Pathogen-Associated Molecular Patterns (PAMPs)

  Surface molecules commonly found on pathogens.

  • Examples include LPS, flagellin, peptidoglycan, teichoic acid, and bacterial and viral nucleic acids.

• TLR-Induced Cytokine Release

  TLRs induce the release of cytokines.

  • Cytokines are chemicals that regulate the intensity and duration of the immune response.

First Line of Defense: Skin & Mucous Membranes

The body’s first line of defense against infections consists of physical barriers and the nonspecific chemicals of the skin and mucous membranes.

Physical Barriers of Defense

• Skin: A Robust Barrier

  The structure of intact skin and the waterproof protein keratin provide resistance to microbial invasion.

  • Dermis

    The inner, thicker portion of skin composed of connective tissue.

  • Epidermis

    Tightly packed layers of skin cells containing a protective protein called keratin.

    • The top layer of cells is dead.
    • Dryness inhibits microbes.
    • Cell shedding removes microbes.

• Mucous Membranes

  Mucous membranes line the gastrointestinal (GI) tract, respiratory tract, and genitourinary tracts.

  • Mucus

    A thick glycoprotein fluid.

    • The lacrimal apparatus protects the eyes from irritating substances and microorganisms.
    • Saliva washes microorganisms from teeth and mouth surfaces.