HOST DEFENCE 1

Question 1

Give examples of viruses? (2)

Answer 1

• Influenza
• Polio mellitus

Question 2

Give some examples of parasites? (3)

Answer 2

• Tapeworms
• Malaria
• Helminths

Question 3

What are the benefits of the immune system? (2)

Answer 3

• Protection from invaders
• Eliminates altered self cells

Question 4

What are the negative effects of the immune system? (2)

Answer 4

• Discomfort (inflammation)
• Damage to self (autoimmunity)

Question 5

What are the two major elements of the immune system?

Answer 5

1. Innate immune system
2. Adaptive immune system

Question 6

List 4 innate defence mechanisms

Answer 6

• Anatomic resisting barriers e.g skin, mucous
• Physiological barriers e.g temp, pH
• Phagocytosis
• Inflammatory defensive barriers e.g vasodilation, increase in capillary permeability, influx of phagocytes

Question 7

What is the role of epithelia in innate immunity? (3)

Answer 7

• Physical barrier
• Antibiotics - locally produced on epithelial tissue
• Intra-epithelial lymphocytes - live on the skin

Question 8

What are the four soluble factors that the innate immune system uses to provide defence against bacterial infections?

Answer 8

• Lysozymes
• Acute phase proteins
• Complement
• Interferons (cytokines)

Question 9

What is the role of lysozymes?

Answer 9

Splits the peptidoglycan wall of susceptible bacteria, this ruptures the extracellular membrane

Question 10

What is the role of acute phase proteins e.g. C reactive protein?

Answer 10

• Opsonization
• Attraction of phagocytes
• Increased blood flow - in areas where there’s a high conc. of foreign pathogens (this brings several chemicals and cells which are required to eliminate potential pathogens) = part of inflammation
• Basically activate complement

Question 11

What are complements?

Answer 11

A group of 20 serum proteins with the role of opsonization

Question 12

What are interferons?

Answer 12

Provide antiviral resistance (break down viral wall)

Question 13

What is opsonization?

Answer 13

Formation of a coating surface around the pathogen, so the pathogen can be identified more easily

Question 14

What cells are part of the innate immune system? (two)

Answer 14

• Phagocytes: engulfs particles
• Natural killer NK cells: recognises cell surface changes occurring on virally infected and tumour cells

Question 15

Where do all cells of the immune system arise from?

Answer 15

Pluripotent hemopoietic stem cells

Question 16

What can pluripotent hemopoietic stem cells differientate into?

Answer 16

1. Myeloid stem cells
2. Lympoid stem cells

Question 17

What can Myeloid cells differentiate into? (2)

Answer 17

• Granulocytic stem cells
• Monocytic stem cells

Question 18

What can granulocytic stem cells differentiate into? (3)

Answer 18

• Neutrophils
• Basophils
• Eosinophils

Question 19

What can monocytic stem cells differentiate into? (4)

Answer 19

• Macrophages
• Langerhans & Kupffer cells
• Dendritic cells

Question 20

What can lymphoid cells differentiate into?

Answer 20

• T cells (T_HELPER T_CYTOTOXIC)
• B cells (plasma cells)

Question 21

How do specialised cells develop from stem cells?

Answer 21

• Cytokine growth factors
• The development of a progenitor cell (committed cell, meaning that it is committed to that line of cell growth)
  
  • e.g. an eosinophil progenitor must become an eosinophil

Question 22

Describe the structure of monocytes?

Answer 22

• Larger than lymphocytes
• Have ONE horseshoe-shaped nucelus
• Often contain faint azurophillic granules

Question 23

What’s the function of monocytes?

Answer 23

Precusor of Macrophages, Langerhans, Kupffer, and Dendritic cells

Question 24

How do macrophages recognise microbes and give an example of a receptor?

Answer 24

Through different Pattern Recognition Receptors (PRR) such as Toll-like receptor.

Question 25

How do macrophages present the antigens of a pathogen on it's surface?

Answer 25

* The macrophage produces an MHC Class II molecules * This binds the degraded peptides of the pathogen and transfers the peptides to the outer surface * So the peptides can be detected by T_h1 cells

Question 26

What are the functions of macrophages? (4)

Answer 26

* Phagocytosis * Intracellular and extra-cellular killing * Tissue repair * Antigen presentation

Question 27

What is the structure of neutrophils? (2)

Answer 27

Are polymorphonuclear * This means they have a nucleus with several lobes and a cytoplasm that contains granules (these granules are not acidic or basic)

Question 28

What is the difference between macrophages and neutrophils? (5)

Answer 28

* Neutrophils aren't antigen-presenting cells * Neutrophils are found in the blood and macrophages are found in the tissue * Neutrophils nucleus has several lobes and macrophage has a horse-shoed nucleus * Neutrophilis has lots of granules * Neutrophilis are at the infected site first

Question 29

What are the four types of PRRs?

Answer 29

* Fc receptors – activate phagocytosis * Complement receptors – bind to C3b-coated bateria and results in enhanced phagocytosis * Scavenger receptors – Bind to polyanions on bacterial surfaces = recognition + phagocytosis * Toll-like receptors – recognize PAMPs + phagocytosis

Question 30

What are the three stages involved in killing of opsonised microbes?

Answer 30

1. . In the innate immune response this occurs via Complement Receptors and in the adaptive immune response by Fc receptors. In both systems, pattern recognition receptors (PRR) are also needed to identify the organism. 2. The microbe is ingested by the pseudopodia of the phagocyte (forms a phagosome) 3. Metabolic reactions take place in phagosome, generating oxygen and nitrogen radicals which damage microbes 4. formation of phagolysosomes = reduction reactions + low pH and lysosomal enzymes = death of microbe

Question 31

In the killing of opsonised microbes, pseudopodia ingest the microbe. How does this differ in innate and adaptive response?

Answer 31

* In innate - complement receptors carry this out * In adaptive - Fc receptors carry this out * Both systems require PRRs

Question 32

What do basophil contain? (2)

Answer 32

* Contain glycogen * Contain deep violet-blue granules (contain histamine and are acidic)

Question 33

Which complements do **basophils** bind?

Answer 33

C3a, C3b and C5a

Question 34

How do eosinophils work?They gather at a parasitic infection or site of allergic reaction such as asthma they release their toxins, contained in their granules

Answer 34

* Eosinophils gather where there is a parasite infection or an allergic reaction such as allergic asthma * They degranulate releasing the contents of their granules (peroxidase and histaminase)

Question 35

How do NK cells know which host cells are infected?

Answer 35

* Virally infected cells inhibit the expression of MHC Class I molecules = reduced expression of MHC class I * Virally infected cells don't respond to IFNα and IFNβ (MHC Class I aren't produced)

Question 36

When both receptors on NK cells are occupied, the NK cell becomes activated. True or false?

Answer 36

False - not activated when both receptors are occupied so doesn't kill virally infected cells

Question 37

When the activating receptor is occupied (not the inhibitory one) what happens?

Answer 37

The NK cells receive a signal to secrete chemicals that kill virally infected cells

Question 38

What's the complement pathway/ overview of innate immune response? (4)

Answer 38

1. Mast cells are activated causing vasodilation and increased capillary permeability to bring immune cells to the site of infection 1. Permeable capillaries allow influx of fluid and cells 2. Phagocytes + neutrophils move to site of inflammation (chemotaxis) 3. Phagocytes and antibacterial destroy bacteria

Question 39

What are cytokines (interferons)?

Answer 39

Toxic to viruses

Question 40

What shows resistance to phagocytosis and how does it do this?

Answer 40

Pneumococcus * Capsular polysaccharide inhibits phagocytosis

Question 41

What shows resistance to reactive oxygen intermediates in phagocytes and how does it do this?

Answer 41

* Staphylococci * Produces catalase which breaks down oxygen intermediates

Question 42

What shows resistance to complement activation (alternative pathway) and how does it do this?

Answer 42

* Neisseria meningitides: expresses sialic acid which inhibits C3 and C5 convertases * Streptococcus: M protein blocks C3 binding to organism and C3b binding to complement receptors

Question 43

What shows resistance to antimicrobial peptide antibiotics and how does it do this?

Answer 43

* Pseudomonas * Synthesis of modified LPS that resists action of peptide AB's