Session 2

Question 1

How do bacteria reproduce?

Answer 1

Binary fission
1>2>4>8
so exponential growth

Question 2

When does bacterial reproduction enter the stationary phase?

Answer 2

When nutrients have run out and toxic waste products accumulate

Question 3

Benefits of flora?

Answer 3

• Produce antimicrobials against harmful bacteria
• Gut flora produce vitamin K, aid digestion and absorption
• Outcompete invading pathogens for receptors and nutrients
• Establishment of a microbiome in newborns stimulates the immune system to develop

Question 4

Negatives of flora?

Answer 4

• Become harmful if displaced. E.g. E.coli from colon can causes cystitis
• If numbers reduce (immunocompromised), then pathogenic/ opportunistic bacteria can cause harm. E.g. Candida albicans overgrowth when lactobacilis numbers reduce.
• Colon flora (sulfatases) can convert food into carcinogenic derivatives. E.g. Cyclamate sweetner > cyclohexamine (bladder carcinogen)

Question 5

Where does our microbiome come from?

Answer 5

• Birth canal through delivery
• Mother’s and other caregivers’ skin
• Breast milk (delivers microbes, vitamins, antibodies and nutrients into the baby’s gut).
• external environment (water, soil, animals, etc.)

Question 6

Physical barriers of the innate immune system?

Answer 6

Skin
Mucous membranes
Ciliated epithelium in the bronchi

Question 7

Physiological barriers of the innate immune system?

Answer 7

Diarrhoea - food poisoning
Vomiting - fp/ meningitis
Coughing - pneumonia
Sneezing - sinusitis

Question 8

Chemical barriers of the innate immune system?

Answer 8

• low pH in the stomach (2), skin (5), and vagina (4.4)

Antimicrobials:

• pepsin in stomach
• lysozyme in sebum (oil), sweat and urine
• IgA in tears, saliva and mucous membranes
• beta defensins of the epithelium (antmicrobial peptide)

Question 9

Biological barriers of innate immune system?

Answer 9

Flora

Question 10

Monocyte vs macrophage

Answer 10

Monocytes circulate in the blood for up to 3 days before migrating into tissues where they become macrophages.

Question 11

How do macrophages recognise pathogens?

Answer 11

Pattern recognition receptors on the pahgocyte surface recognise/bind either:

• opsonins
• PAMP’s, pathogen- associated molecular patterns

Question 12

‘PRR’s recognise PAMP’s’

Explain

Answer 12

Pattern recognition receptors (TLR’s) on the surface of (phagocytes) neutrophils, macrophages etc. bind pathogen-associated molecular patterns on the microbe surface. (LPS, peptidoglycan).

Question 13

Match the pattern recognition receptor (PRR) and PAMP;

• LPS
• Lipoproteins
• Peptidoglycan
• Flagellin

Answer 13

LPS = TLR4 
Lipoproteins = TLR2 

Peptidoglycan = TLR2

Flagellin = TLR5

Question 14

Examples of Opsonins

Answer 14

Antibodies (IgM 1st, IgG chronic)
CRP (acute phase)
MBL, mannose binding lectin (acute phase)
C3b

Question 15

IgM :IgG ratio

Answer 15

IgM is the first antibody to appear at a foreign antigen

IgG is only present if the infection has occurred before

Question 16

3 ways the complement system can be activated?

Answer 16

Classical pathway
Alternative pathway
Lectin pathway

Question 17

What is MBL, mannose binding lectin?

Answer 17

MBL is a lectin (protein that binds carbohydrates) which binds D-mannose on pathogen membranes. It acts as an opsonin and initiates the complement cascade via the lectin pathway.
It binds to Candida albicans (yeast), HIV (virus) and Salmonella (bacteria) etc.

Question 18

What initiates the alternative pathway of the complement cascade?

Answer 18

Binding endotoxin (on E.coli)

Question 19

What initiates each?
Classical pathway
Alternative pathway
Lectin pathway

Answer 19

1) antigen antibody complex (IgM/IgG)
2) endotoxin
3) mannose binding lectin, MBL

Question 20

Roles of each:
C3a, C4a, C5a
C3b (+ C4b)
C5-C9

Answer 20

1) stimulate vascular leakage and attract neutrophils to site of injury (chemotaxins)
2) opsonins
3) membrane attack complex; punches holes in bacterial cell membranes

Question 21

Cytokines released from macrophages?

Answer 21

Il-6, TNF-alpha. Il-1

Question 22

What are the systemic and local effects of cytokine release from macrophages?

Answer 22

TNF-alpha, Il-1, Il-6

Local effects are vasodilation of arterioles, vascular permeability and upregulated adhesion molecules within vessels to allow neutrophil migration into the tissues (selectins and integrins)

Systemic effects are upon the;

• liver (stimulate CRP and MBL production)
• hypothalamus (raise body temperature)
• bone marrow (increase neutrophil mobilisation [release])

Question 23

Asplenic pateints are particularly susceptible to which type of infection?

Answer 23

Pneumococcal / Streptococcus pneumoniae because it’s encapsulated

Question 24

Opsonin and PAMP mediated phagocytosis by neutrophils is an important part of the innate immune response.
What could reduce the levels of phagocytosis?

Answer 24

Reduced spleen function
- hyposplenic/ asplenic patients

Less neutrophils

• chempotherapy
• phenytoin (anti-convulsant)
• leukaemia and lymphoma

Reduced neutrophil function

• Chronic granulomatous disease (no respiratory burst)
• Chediak- Higashi syndrome (no phagolysosome)