The Immune System Flashcards Preview

ESA 1 - Body Logistics > The Immune System > Flashcards

Flashcards in The Immune System Deck (11)
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1
Q

Describe the process of phagocytosis.

A
  1. Chemotaxis and adherence of pathogen to phagocyte.
  2. Phagocytosis and phagolysosome formation.
  3. Phagosome-lysosomes fusion, forming a phagolysosome.
  4. Pathogen degradation.
  5. Formation of residual body containing indigestible material and exocytosis.
2
Q

Describe the processes used in the phagolysosome to destroy a pathogen.

A

O2 dependent degradation

  • Respiratory burst produces reactive oxygen & nitrogen species.
  • E.g. Oxidase catalyses reduction of O2 to superoxide anion - very toxic to pathogens. Superoxide anion also generates other powerful oxidising agents, inc. hydroxyl radicals and hydrogen peroxide. Myeloperoxidase produces hyperchlorite from hydrogen peroxide and chloride ions - toxic.
  • E.g. Production of nitric oxide.

O2-independent degradation
- Requires release of granules containing proteolytic enzymes such as defensins, lysozyme and cationic proteins.

3
Q

What is opsonisation?

A

Pathogen is marked for phagocytosis using opsonins such as antibodies or complement (C3b).

4
Q

What are the 3 pathways of complement and how are these activated?

A
  • Classical pathway: antigen-antibody complexes bind to pathogen surface
  • Lectin pathway: mannose-binding lectin binds mannose of pathogen surface
  • Alternative pathway: C3b binds directly to cell surface
5
Q

At which point do the 3 complement pathways converge?

A

Proteolysis of C3 into C3a and C3b by C3 convertase.

6
Q

What are the main immune effects of complement?

A
  • C3a and C5a: inflammation and phagocyte recruitment
  • C3b: pathogen opsonisation (binds to complement receptors on phagocytes)
  • C5b & other terminal complement components: membrane-attack complex forming pore in pathogen membrane (lysis).
7
Q

Which cells are the main mediators of the innate immune system?

A
  • Neutrophils = front-line effector cells, mediate phagocytosis.
  • Macrophages = mediate phagocytosis and act as APCs.
8
Q

Which cells are the main mediators of the adaptive immune system?

A

Lymphocytes:

  • B cells - secrete antibodies
  • T cells - kill virus-infected cells and cancer cells, and activate other IS cells.
9
Q

How do T cells mediate infected cell killing?

A

Killer T cells produce:

  • perforins - proteins that form pores in the membrane of target cells
  • granzymes - proteases that induce PCD on entry into target cells
10
Q

How are T cells activated?

A
  • Lymphatic fluid drains through lymph nodes, carrying dendritic cells with it. T cells migrating through the lymph nodes recognise antigen on these antigen-presenting DCs - form germinal centres.
  • Interaction mediated by MHC II molecules.
11
Q

How are B cells activated?

A

By antigen recognition followed by function of activated T helper cells in germinal centres.