The Immune System Flashcards Preview

ESA 1 - Body Logistics > The Immune System > Flashcards

Flashcards in The Immune System Deck (11):
1

Describe the process of phagocytosis.

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

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

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

What is opsonisation?

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

4

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

- 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

At which point do the 3 complement pathways converge?

Proteolysis of C3 into C3a and C3b by C3 convertase.

6

What are the main immune effects of complement?

- 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

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

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

8

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

Lymphocytes:
- B cells - secrete antibodies
- T cells - kill virus-infected cells and cancer cells, and activate other IS cells.

9

How do T cells mediate infected cell killing?

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

How are T cells activated?

- 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

How are B cells activated?

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