IAH2 - Physical microbiological and chemical barriers to infection

Question 1

Functions of immune system

Answer 1

Recognition of non-self antigens
Effector function to eradicate or control infection
Regulation to provide an appropriate response
Memory to allow better response next time

Question 2

Before the innate immune system is activated what protects against infection?

Answer 2

Physical, chemical and microbiological barriers

Question 3

List the physical and chemical barriers to infection

Answer 3

Skin - keratinised epithelium (dry surface inhibits growth, desquamation gets rid of bacteria)
Skin - lactic acid from sweat and FA from sebaceous glands = low pH inhibit bacterial growth
Mucosal tissues = mucin and ciliated epithelium
Mucosal tissues = flow of air (airways) or fluids (urogenital tract) to wash out microbes
GI tract = acidic and digestive enzymes
SI = Paneth cells = AMPs (and lysozyme and phospholipase)
Mouth mucosa = saliva, GCF

Question 4

How does cystic fibrosis compromise physical barriers?

Answer 4

Abormally thick mucosa leading to lung infections

Question 5

What microbiological barriers fight infection? Where are they found?

Answer 5

Commensal bacteria in mouth and gut compete with pathogens for nutrient and space
Some commensal bacteria release substances with bactericidal properties e.g. lactobacilli release lactic acid

Question 6

If microbiological barriers are compromised what infection can occur?

Answer 6

C. diff when commensal bacteria are killed by antibiotics

Question 7

List 3 soluble mediators of innate immunity (molecular elements)

Answer 7

Enzymes
Complement
AMPs

Question 8

Function of

a) lysozyme
b) phospholipase

Answer 8

a) digest cell wall

b) digest membrane

Question 9

Function of complement

Answer 9

Lysis, opsonisation and chemotaxis

Question 10

Mechanism of action for AMPs

Answer 10

Disrupt cell membrane as a result of amphipathic properties and cause cell lysis

Question 11

Cells producing AMPs

Answer 11

Paneth cells, neutrophils and epithelial cells

Question 12

Cellular elements of innate immunity?

Answer 12

Phagocytosis by neutrophils and NK cells

Question 13

How do neutrophils recognise pathogen?

Answer 13

Coated in complement = complement receptors

Coated in antibodies = Immunoglobin Fc receptors

Question 14

How does complement cause lysis?

Answer 14

Formation of membrane attack complex on bacteria outer membrane = forms pits and then dies