Innate Immune System

Question 1

What three factors determine the outcome of the host-pathogen relationship?

Answer 1

1. Infectivity
2. Virulence
3. Host’s immune response (pathogen recognition, containing/eliminating infection, regulation of self, memory for pathogens)

Question 2

Innate immunity involves which 4 first lines of defence?

Answer 2

1. Biological barriers
   Normal flora, non-pathogenic microbes- compete with pathogens, antimicrobial, synthesise vitamins
2. Physical barriers
   Skin, mucous membranes, bronchial cilia

3. Chemical barriers 
Low pH (skin, stomach, vagina), antimicrobial molecules: IgA, lysozyme, mucus, beta-defensins, gastric acid and pepsin 

4. Physiological barriers
   Diarrhoea, vomiting, coughing, sneezing

Question 3

When can problems with these innate immune barriers occur?

Answer 3

When normal flora is displaced from its normal location

In high risk patients (asplenic/hyposplenic patients)

Question 4

What are some of the second lines of innate immune defences?

Answer 4

Chemicals:

• Complement pathways (C1-C9)
• Chemoattraction - TNF-alpha, IL-1, IL-6

Phagocytes:

• PAMPs and PRRs
• Opsonisation (CRP, C3b, C4b, IgG, MBL)
• Engulfment (O2 dependent/O2 independent)

Question 5

What effect do cytokines such as TNF-alpha, IL-1 and IL6 have on inflammatory responses associated with innate immunity?

Answer 5

Liver- opsonins
Bone marrow- neutrophil migration
Blood vessels-vasodilation, vascular permeability, attraction of neutrophils, adhesion molecules
Hypothalamus- increased body temperature

Question 6

How does the oxygen dependent pathway differ from the oxygen independent pathway of microbe destruction?

Answer 6

Oxygen dependent: respiratory burst, oxygen radicals: H2O2, NO, superoxide

Oxygen-independent: lysozyme, enzymes

Question 7

What bacteria are a particular risk to asplenic patients?

Why?

Answer 7

LPS encapsulated bacteria

Imparied opsonization, reduced phagocytosis and reduced clearance from the blood stream by IgM

Question 8

Asplenic patients are generally recommended to be vaccinated against which three bacteria?

Answer 8

Neisseria meningitidis
Haemophilus influenzae
Streptococcus pneumoniae
“NHS”