25A17: Exam Report

  1. Define innate immunity including how it differs from adaptive immunity (10% of marks).

  2. Outline the components of the innate immune system including their role in the immune response (90% of marks).

59% of candidates passed this question.

  1. A good definition of innate immunity included the following information: present at birth, non- adaptive and responds to a limited set of foreign molecules. For full marks, it was expected that candidates would contrast this with the adaptive immune response including the requirement for sensitisation / pre-exposure and potential to respond to many unique antigens.
  2. It was helpful to divide the components of the innate immune system into physiochemical, humeral and cellular elements. Physiochemical elements included skin, mucus, cilia and secretions such as gastric acid. Additional marks were allocated for answers which also mentioned how each component acts to prevent infection (i.e. skin forms a physical barrier which prevents bacterial translocation). This part was generally answered very well. For humoral elements marks were apportioned between complement, lysosymes and acute phase proteins / Negative phase proteins. A brief outline of each was desirable with full marks given for detailed description of their role in immunity including their sites of production Lastly a good description of cellular elements included neutrophils, macrophages/monocytes, mast cells and natural killer cells. For each a brief outline of their role and function attracted full marks.

24A17: Exam Report

Innate Immunity

  1. Define innate immunity including how it differs from adaptive immunity (10% of marks).
  2. 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:

  1. a definition of innate immunity featuring its presence since birth, the non-specificity and lack of memory when compared with the adaptive immune system,
  2. 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 / 25A17 / 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