24A17: Exam Report

Innate Immunity
(a) Define innate immunity including how it differs from adaptive immunity (10% of marks).
(b) Outline the components of the innate immune system including their role in the immune response (90% of marks).

17% of candidates passed this question.

Expectations for a high scoring answer were:

  • (a) a definition of innate immunity featuring its presence since birth, the non-specificity and lack of memory when compared with the adaptive immune system,
  • (b) an outline of different components of innate immune system including; physicochemical (skin, mucus, cilia, gastric acid), humoral (lysosome, complement, acute phase proteins) and cellular (neutrophils, macrophages, natural killer cells, mast cells). In addition to listing a number of these examples, a brief explanation (“outline”) of their function should be included.

S1ii / 24A17: Innate Immunity

(a)

  • Innate immunity is the defense system with both humoral, cellular and physiochemical elements. Unlike adaptive immunity it; is non-specific, rapid, does not display memory, and is present from birth.
  • It interacts with the adaptive immune system, can amplify and enhance B/T-cell activity, but is functional in its absence.

(b) Components:

Physiochemical barriers

  • Skin – to prevent entry of pathogens, also host flora to prevent opportunistic pathogens.
  • Mucosal lining – hostile environment for pathogens with mucous production and tight junctions.
  • Gastric acid – low pH prevents pathogen survival/replication.
  • Cilia – actively remove pathogens from the respiratory system.
  • – -> works in conjunction with cough reflex to expel pathogens.

Humoral

Circulating components act as non-specific defence mechanisms such as

  • Complement
    • A circulating protein cascade which is triggered by lectin/cell walls of fungi or bacteria or by immunoglobulins.
    • Forms a destructive complex.
    • Triggers adaptive responses (chemotaxis – the attraction of other components or opsonisation – the highlighting of a pathogen to B/T-cells
  • Lysosomes (exist to destroy foreign cells → found in saliva, breaks down bacterial cell walls)
  • Acute Phase Proteins: Important mediators of inflammation. IL-6 is the primary cytokine responsible for inducing their production in the liver

Cellular

Cells that are part of innate immunity include:

  • Natural killer cells: Detect cells that are infected/malignant and destroy them.
  • Macrophages: Such as neutrophils/monocytes – engulf pathogens, facilitating their detection/destruction.  Release cytokines to recruit other cells
  • Mast cells: Found in mucous membranes & connective tissue. Release histamine and other chemokines, accelerating defensive response i.e. vasodilation, attraction of inflammatory factors.  Alter other immune cells (neutrophils/Macrophages) to make their way to infective area
  • Eosinophils: Secrete highly toxic proteins & free radicals which kill bacteria and parasites.

References: Ganong, Basic Physiology for Anaesthetics (Huang, Matthews)

Author: Brodie Farrow