Foundation - Immunology

Question 1

Distinguish between innate and adaptive immunity

Answer 1

1. Almost immediate VS time needed to form
2. Fully mature at birth VS immature at birth
3. First exposure, not long-lasting VS lasting protection
4. Low specificity VS high specificity
5. Recognition by PAMPs VS recognition by antigens
6. Inherited in germ line VS develop somatically
7. No memory VS immunological memory
8. Perfect discrimination VS very good but occasionally fail (autoimmunity)
9. Mediated by neutrophils mast cells, basophils, eosinophils, macrophages, NK cells, dendritic cells VS B and T lymphocytes

Question 2

Describe the role of the lymphatic system

Answer 2

1. Help carry away exudate and injurious stimuli and drain into lymph nodes for further deactivation by immune system during inflammation
2. Drain excess interstitial fluid
3. Transport dietary lipids and lipid-soluble vitamins from GIT to blood

Question 3

Name the primary lymphoid organs and their functions

Answer 3

Bone marrow and thymus
1. Where cells are produced
2. B and T cells mature
3. Naive cells are present

Question 4

Name the secondary lymphoid organs and their functions

Answer 4

Lymph nodes, spleen, mucosa-associated lymphoid tissues (MALT) in submucosal membrane sites, Peyer’s patches in small intestine
1. Where antigen presentation occurs
2. Where immune responses are coordinated
3. No naive cells present

Question 5

Define innate immunity

Answer 5

Preformed soluble and cellular components that provide a rapid response against pathogens

Question 6

Name the innate barriers of the body
(i) Defensins
(ii) Skin
(iii) Mucous membranes
(iv) Airways
(v) Tears and saliva

Answer 6

(i) Body’s antibiotic peptide found in tears, saliva, sweat → adheres to bacterial cell surface → forms pores → induce osmotic lysis

(ii) Constant shedding and renewal (every 48 hours); high salt content; keratin layer with commensal bacteria that competes with microbes for nutrients; IgA found in sweat

(iii) Blockage of pathogen attachment sites; mucous binds to and traps bacteria and fungi → shedding

(iv) Ciliated cells constantly beat, wafting mucous with trapped microbes upwards and outwards; mucous contains mucin that trap microbes and antimicrobial proteins (lysozymes, defensins); cough reflex

(v) Lysozymes hydrolyse polysaccharide component of bacterial and yeast cell wall especially in phagocytic cells

Question 7

Describe the recognition of microbes by innate immune system

Answer 7

Pathogen-associated molecular patterns (PAMPs)
- Conserved molecular patterns shared by broad classes of pathogens
- Recognised by Toll-like receptors expressed on all innate immune cells

Danger/damage-associated molecular patterns
- Signals released from stressed/damaged host cells
- Recognised by various receptors

Question 8

Name some examples of PAMPs

Answer 8

Bacteria: flagellin, lipopolysaccharide

Virus: dsDNA, ssRNA

Fungi: zymosan

Protozoa: profilin-like molecule

CpG DNA (rich in bacteria/virus DNA)

Question 9

Name the various Toll-like receptors and the type of PAMPs they recognise

Answer 9

TLR2: Gram pos bacteria glycolipids and peptidoglycan + parasite

TLR3: dsDNA

TLR4: LPS of Gram neg bacteria

TLR5: flagellin

TLR7/8: ssDNA

TLR9: unmethylated CpG DNA

C-type lectin: microbial polypeptide

RIG-like receptor: viral RNA

NOD-like receptor: bacterial cell wall lipid + products of damaged host cell

Question 10

Name some examples of DAMPs

Answer 10

Purine metabolites from cytoplasm (e.g. ATP, adenosine, uric acid)

DNA, proteins associated with DNA from chromatin

HMGP1 from chromatin/ lysosomes of stressed cells

Question 11

Name the various receptors and the type of DAMPs they recognise

Answer 11

TLR4: uric acid
TREM-1: heat shock proteins
RAGE: advanced glycation end products, HMGP1