Innate Defences

Question 1

What are the barriers to infection?

Answer 1

Mechanical: Epithelial cells, airflow, mucus, cilia and tears.
Chemical: Fatty acids, enzymes, defensins and lysozyme.
Flora

Question 2

What are the two regulators of the innate immune system?

Answer 2

Plasma factors - Complement pathway

And cellular factors - Inflammation and anti-pathogen defense via dendritic and natural killer cells

Question 3

What are the main features of innate immunity?

Answer 3

• Rapid
• No memory
• First line of defence
• Warning sign for adapative immune system
• Recognition of non-self patterns – fairly non-specific response

Question 4

What are Pattern Associated Molecular Patterns?

Answer 4

PAMPs are molecules that are recognised by the immune system to stimulate the immune response.

Question 5

What are some examples of pattern recognition receptors?

Answer 5

• Mannose receptor
• Scavenger receptor
• C-type lectin-like receptors
• Toll like receptors (found on macrophages and dendritic cells, humans have 10)
• Cystoplasmic NOD-like receptors

Question 6

What are the two main soluble PRRs?

Answer 6

Collagen containing C-type lectins / Collectins / Mannose - Bind to mannan and opsonise microorganisms for phagocytosis

Defensins - Can be alpha or beta. Have broad antimicrobial activity.

Question 7

What are membrane bound signalling receptors?

Answer 7

Receptors on membranes of intracellular vesicles. They recognise PAMPs and induce the expression of cytokines and chemokines.

Question 8

What is the purpose of cytoplasmic signalling receptors? What are two examples?

Answer 8

Cytoplasmic signalling receptors detect intracellular bacteria and viruses. Include; NOD-like receptors for detecting infection and RIG-I like helicase for sensing RNAs in the cytoplasm.

Question 9

What are the three phagocytic receptors?

Answer 9

1. Complement receptor
2. Scavenger receptor
3. Mannose receptor

Question 10

What is the phagosome?

Answer 10

The phagosome is the membrane enclosed endocytic vesicle.

Question 11

What does lysosome fusing with phagosome make?

Answer 11

Phagolysosome

Question 12

How does phagocytosis occur?

Answer 12

Lysosomes have proteases to breakdown bacterial walls.

Question 13

What is opsonisation?

Answer 13

The coating of bacteria to enhance phagocytosis. Phagocytic cells can then recognise molecular tags of FcR or CR1 and enhance adherance

Question 14

What are opsonins?

Answer 14

Opsonins are soluble proteins that bind to pathogens. Examples include; IgG, IgA antibodies and C3b.

Question 15

What is the complement system?

Answer 15

The complement system is when proteins are activated in a cascade to mark a pathogen for killing.

Question 16

What are the outcomes of the complement system?

Answer 16

• Migration of phagocytes to site of infection
• Opsonisation and phagocytosis of microorganisms
• Direct lysis of pathogens

Question 17

What are the three pathways of the complement system?

Answer 17

1. Classical Pathway
2. Lectin pathway
3. Alternative Pathway
   These converge when C3 is activated.

Question 18

What does the cleavage of C3:C3A do?

Answer 18

The cleavage of C3:C3a induces inflammation, increases blood vessel permeability allowing for protein leakage and phagocytes recruitment.

Question 19

What does the cleavage of C3:C3b do?

Answer 19

After the cleavage of C3:C3b, the C3b remains on the microbe. This allows for the uptake/destruction of pathogens by phagocytes, specific recognition of the complement on the pathogen and opsonisation via complement receptors.

Question 20

What is the membrane attack complex?

Answer 20

The membrane attack complex is a pore in the lipid bilayer membrane. This destroys membrane integrity and alters the proton gradient.

Question 21

What are Neutrophils?

Answer 21

Most common white blood cell.
Lifespan of 8hrs.
Critical for first line of defense against bacteria.
Pus is dead neutrophils, as they die fighting. Once they die they release mediators, attracting more neutrophils. Express receptors for complement and antibody receptors

Question 22

What are eosinophils?

Answer 22

Fight parasites and cause allergic response.

Release granules when triggered and contain a range of cytotoxic compounds to kill the parasite.

Question 23

What are granulocytes?

Answer 23

Granulocytes include; neutrophils, eosinophils and basophils

Question 24

What are basophils?

Answer 24

Used in allergic responses by releasing histamines which causes inflammation.

Question 25

What are the functions of macrophages?

Answer 25

Quickly phagocytose microbes and secrete chemical mediators.
Present antigens to t-cells.
Repair tissues and regulate homeostasis.
Contribute to humoral immune response and cell-mediated immunity.
Produce ROS, NO (nitric oxide), bacterial enzymes, lysozymes, defensins and lysosomal acid hydrolases to degrade phagocytes

Question 26

How do extracellular pathogens evade phagocytosis?

Answer 26

• They have a thick polysaccharide capsule
• Can’t be recognised by PRR (might still be recognised by the complement system)
• Some pathogens prevent the fusion/ acidification of the lysosome and phagosome

Question 27

What are immature/ resting Dendritic cells?

Answer 27

Dendritic cells that are phagocytic, have PRRs and are a sample environment for the antigen.

Question 28

What are mature dendritic cells?

Answer 28

Mature dendritic cells undergo morphological changes, migrate to the lymph nodes, present antigens to t-cells and produce cytokines.

Question 29

What are the functions of natural killer cells?

Answer 29

Natural Killer Cells: Can remember a pathogen.

• Recognize IgC coated target cells and cells with down regulated/ less MHC, stressed cells or cells with DNA damage.
• This prevents attacking of normal cells, as it will know something is wrong with them.