innate immunity

Question 1

what is the innate immune system?

Answer 1

fast, non-specific immediate response to any foreign pathogen that breaks the line of defence

Question 2

what are the first lines of defence in the innate immune system?

Answer 2

1) Physical barriers – skin, mucous membranes and bronchial cilia
2) Physiological barriers – diarrhoea, vomiting, coughing and sneezing
3) Chemical barriers – low pH and antimicrobial molecules such as IgA, lysozyme, mucus, β-defensins and gastric acid
4) Biological barriers– normal flora in strategic locations which provide us with several benefits including synthesise of some vitamins (e.g. K, B12) and immune maturation

Question 3

How can normal flora result in infection?

Answer 3

1. normal flora is displaced from its usual location to another environment which may be sterile,
2. the host becomes immunocompromised and the normal flora can start to overgrow and become pathogenic
3. when normal flora is depleted due to antibiotic treatment

Question 4

what is the second line of defence in the innate immune system?

Answer 4

1) Phagocytes – macrophages, monocytes, neutrophils
2) Other key cells of the innate immune system - basophils (mast cells),
eosinophils, natural killer cells and dendritic cells
3) Chemicals – complement system and cytokines

Question 5

what allows phagocytes to recognise microbes as foreign?

Answer 5

molecules on the microbe surface known as PAMPs - pathogen associated molecular patterns
PRRs - pathogen recognition receptors are receptors on phagocytes which detect the PAMPs

Question 6

what is opsonisation?

Answer 6

enhances the interaction between the phagocyte and the microbe
opsonins are proteins that bind to and coat the surface of the microbe

Question 7

what produces opsonins?

Answer 7

various components of the immune system:
complement proteins (C3b, C4b), antibodies (IgG, IgM), and acute phase proteins (C-reactive protein (CRP), mannose-binding lectin (MBL))

Question 8

what happens when the phagocyte has recognised and bound to the microbe?

Answer 8

destroy the microbe by a process of engulfment and digestion of the microbe. It destroys the microbe either by
1) oxygen dependent pathway – free oxygen radicals
2) oxygen independent pathways – enzymatic digestion

Question 9

what are the different complement proteins which are involved in destruction of pathogens?

Answer 9

1) C3a/C5a – which are responsible for recruitment of phagocytes
2) C3b/C4b – opsonisation of pathogens
3) C5 – C9 – killing of pathogens

Question 10

what is the complement system?

Answer 10

complement system proteins circulate in blood in inactive form + are activated by 2 distinct pathways:
a) alternative pathway – initiated by cell surface components such as endotoxins in E.Coli or
b) MBL – initiated when MBL binds to mannose sugar components of proteins on microbes

Question 11

what is the role of cytokines in the innate immunity?

Answer 11

produced by macrophages (IL-1/IL-6 and TNFα)
have a role to play in inflammation

Question 12

which chemical mediators cause Vasodilatation?

Answer 12

Histamine
Serotonin
Prostaglandins
Nitric Oxide

Question 13

which chemical mediators cause increased vessel permeability?

Answer 13

Histamine
Bradykinins
Leukotrienes
C3a & C5a

Question 14

which chemical mediators are involved in chemotaxis?

Answer 14

C5a
TNF-a
IL-1
Bacterial Peptides

Question 15

which chemical mediators are involved in causing fever?

Answer 15

Prostaglandins
IL-1
TNF-a
IL-6

Question 16

which chemical mediators are involved in causing pain?

Answer 16

Bradykinin
Substance P
Prostaglandins