12. Immunology

Question 1

List out the innate immunity cells:

Answer 1

1. Macrophages
2. Neutrophils
3. Dendritic cells
4. NK cells
5. Mast cells, basophils, eosinophils

MNDNMBE

Question 2

What are our adaptive immunity cells?

Answer 2

1. B cells: antibody secretion
   - IgM: pentamer, more prevalent in primary infection
   - IgG: monomer, more prevalent in secondary infection
   - IgA: dimer, bound to J chain (protect mucosal surfaces, e.g. saliva)
   - IgE: monomer (mast cell degranulation => driver of asthma/allergies)
2. T cells
   - CD4 T cells (helper): secrete cytokines => help B cells make Ab => coordinate antigen-specific adaptive response
   - CD8 T cells (cytotoxic): kill infected cells via lysis, require perforin & gransyme
   * T cells involved in BOTH cellular & humoral immunity (help B cells make Ab)

Question 3

What do CD4 T cells recognise? (Antigen presentation)

Answer 3

EXOgenous antigens on MHC Class II
- exogenous antigens inhaled/ingested/secreted by microbes, then taken up by dendritic cells

Question 4

What do CD8 T cells recognise? (Antigen presentation)

Answer 4

ENDOgenous antigens on MHC Class I
- endogenous antigens generated within cells

Question 5

What does a cytotoxic T cell release to kill?

Answer 5

Releases perforin & granzyme

Question 6

What cell presents antigens to immune cells of the body?

Answer 6

Dendritic cells
- presents antigens to T lymphocytes (APC)

Question 7

Selective IgA deficiency most likely leads to

Answer 7

Sinusitis

Question 8

Intravenous fluid contaminated by which substance found in bacterial cells can result in signs and symptoms of septic shock, even if no viable bacteria is found?

Answer 8

Lipopolysaccharide

• it induces pdn of prostaglandins => fever

Question 9

Removal of which organ will cause an increased risk of infection by encapsulated bacteria like Strep Pneumoniae?

Answer 9

Spleen.
- cuz it fights any invading germs in blood

Question 10

Which cell is cytotoxic and kills infected cells without the need for adaptive immunity response?

Answer 10

NK cells

• cytotoxic, induce apoptosis of virus-infected & tumour cells

Question 11

What are antigens made of?

Answer 11

An antigen is just a molecule that can stimulate a response
- antigens are usually proteins

Question 12

Immune system is not inherited from parents but..

Answer 12

Developed during the lifetime of an individual

Question 13

What does CD number mean?

Answer 13

Cluster of Differentiation.
CD numbers are used to define cell types.

Question 14

Name the secondary lymphoid organs:

Answer 14

1. Lymph nodes
2. Spleen

Question 15

What are the targets recognised by dendritic cells?

Answer 15

Innate immunity targets:
1. PAMP: produced by pathogens, do not evolve rapidly, not shared w host
- pathogen associated molecular patterns
2. DAMP: host cell components released by damaged/stressed tissues
- damage associated molecular patterns

Question 16

What happens if you remove the spleen?

Answer 16

Increased risk of infection by encapsulated bacteria like S. Pneumoniae

Question 17

What are interferons, + specifically Type I interferon?

Answer 17

• type of cytokine, part of innate immune system
• released by infected cells early on during viral infection => increases resistance of neighbouring cells against infection
• inhibits viral replication
• IL-6 stimulates secretion of C reactive proteins

Question 18

What are Lysozymes?

Answer 18

• powerful digestive enzymes that destroys the polysaccharides that coat the outer wall cell wall of bacteria
• secreted in tears and cells
• also a major enzyme component in egg whites, why eggs dont get infected.

Question 19

What do TLR-4 on our dendritic cells and macrophages detect for?

Answer 19

Lipopolysaccharidse (LPS), thus, detecting presence of gram -ve bacteria

Question 20

What do Neutrophils do?

Answer 20

• most abundant immune cell
• comes in first wave of leukocytes to enter infected sites via blood
• survives only 48hrs
• basically ur first responders to sites of infection
• kills microbes using similar mech as macrophages (phagocytosis + bactericidal mechs)

Question 21

Which cell links the innate to the adaptive immune system?

Answer 21

Dendritic cell

Question 22

How is the Innate immune system linked to the Adaptive immune system?

Answer 22

1. Dendritic cell captures pathogenic/intruder material in tissues, processes the material (digests, smashes n displays itself w protein fragments)
2. Then Dendritic cell migrates into regional lymph node via afferent lymphatics
3. Specific lymphocyte (the one) in lymph nodes encounters dendritic cell displaying recognised pathogen peptide
4. Formation of stable synapse => stimulates lymphocyte to proliferate & differentiate

Question 23

What is the chronology of an immune response?

Answer 23

1. Break in barrier defence => infiltration of microbes into site
2. Detection of PAMP & DAMP via innate immune receptors
3. Release of cytokines & chemokines by macrophages at site
4. Infiltration of neutrophils from blood
5. Migration of dendritic cells from infected site to local draining lymph nodes
6. Initiation of adaptive immune response (B & T cells)

Question 24

How do CD4 T cells (helper) react?

Answer 24

• secrete cytokines => help B cell make Ab => coordinate antigen-specific adaptive response

Question 25

How do CD8 T cells (cytotoxic) **react**?

Answer 25

- kill infected cells via lysis, require perforin & granzyme - it pokes holes in the cells n causes it to lyse and leak

Question 26

How do antigens enter via the gut?

Answer 26

1. Microfold cells - uptake of antigens into gut via endocytosis - antigens bind to dendritic cells in ‘pocket’ of Microfold cells => activation of T cells 2. Dendritic cells - extend processes across epithelium => **capture antigen on gut mucosa** * mucosa pathogens can enter via M/dendritic cells

Question 27

Name the components of Gut Associated Lymphoid Tissue (GALT)

Answer 27

1. Specialised antigen uptake e.g. microfold cells, dendritic cells 2. Large no. of lymphocytes - epithelium: mainly CD8 T cells - lamina propria: mainly CD4 T cells 3. Peyer’s patches - in small intestine - rich in B cell folliclces, smaller T cell areas 4. Humoral immunity - IgA>IgM>IgG (IgA prevents bacterial adhesion & directly inactivates virus)

Question 28

What are the functions of antibodies?

Answer 28

- immune complex & agglutination => trap pathogens (IgM, IgG) - complement activation by binding to target cells (IgM) - opsonisation (coat pathogen in Ab) => enhance phagocytosis (IgG) - neutralisation of bacteria/toxins/viruses, by blocking binding (IgG, IgA) - Ab-dependent cellular cytotoxicity (ADCC) - Mast cell degranulation (IgE)

Question 29

A child has dengue 3 days ago, which immunoglobulin will be high?

Answer 29

IgM (response to new antigen)

Question 30

What does the complement system do?

Answer 30

- **aid phagocytes & Ab in killing pathogens** - activation: lysis, phagocytosis, opsonisation, clear immune complex (e.g. type III hypersensitivity) => NO stimulation of Ab pdn The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane.