B cell humoral immunity and vaccination

Question 1

LO

Answer 1

• Describe the kinetics of the humoral immune response
• Identify the key cell types and receptors involved in a humoral immune response
• Describe the generation of class-switched, high-affinity antibody
• Describe the different types of vaccine
• Explain how vaccines induce protective immune responses

Question 2

B cell immunity lecture 1 topics

Answer 2

B cell response

• Humoral response
• Type of antigens
• Role of T-cell help
• GC reaction and antibody affinity maturation
• Alternative help to B cells
• Antibody isotypes

Other roles of B cells (not relevant to humoral response

Question 3

Tell me the following features of the primary immune response

• Time lag after immunisation
• Peak response
• Antibody isotype
• Antibody affinity
• Induced by
• Required immunisation

Answer 3

Time lag: usually 5-10 days

Peak response: Smaller

Antibody isotype: Usually IgM > IgG

Antibody affinity: Lower average affinity, more variable

induced by: all immunogens

Required immunisation: relatively high doses of antigens, optimally with adjuvants (for protein antigens)

Question 4

Tell me about the following features of the secondary immune response

• Time lag after immunisation
• Peak response
• Antibody isotype
• Antibody affinity
• Induced by
• Required immunisation

Answer 4

Time lag: usually 1-3 days

Peak response: larger

Antibody isotype: relative increase in IgG and, under certain situations, in IgA or IgE

Antibody affinity: high average affinity (affinity maturation)

induced by: only protein antigens

Required immunisation: low doses of antigens; adjuvants may not be necessary

Question 5

Why is the secondary immune response limited to protein antigens?

Answer 5

Requires new T-cell help and only needs low doses

This secondary response is dominted by IgG class switched antibodies

Question 6

Tell me about the affinity and avidity of IgM and IgG antibodies

What are the general structures of each as well

Answer 6

IgM are pentameric, low affinity, not gone through germinal centre reaction, high avidity. These can be pentameric or sometimes hexameric

IgG are high affinity but low avidity, affinity isn’t needed to be heightened via pentameric structure. These are large globular proteins

Avidity: The accumulation strength of multiple affinities of multiple interactions e.g., between protein receptor and its ligands

Question 7

What three different things help to traffick the antigen to the secondary lymphoid organs?

Roughly what size are each?

Answer 7

• Small soluble protien antigens (70kDa/ 5-6nm)
• Small particular antigens (20-200nm)
• Large particular antigens (200-500nm)

Question 8

Tell me about small soluble protein antigens

Answer 8

enter lymphatic system via pores

passive drainage to lymphoid organs

independent of antigen presenting cells

once at the secondary lymphoid organs they can enter through specialised conduits

captured by macrophages and lymph node resident DCs

Question 9

Tell me about small particular antigens

Answer 9

• Enter lymphatic system via pores
• Passive drainage to lymphoid organs
• Transported into secondary lymphoid organs by myeloid or B cells

Question 10

Tell me about large particular antigens

Answer 10

Too large to enter via pored

Transported via peripheral DCs through lymphatic system

Not clear how they are transported: on surface? Or internalised?

Can take up to 24 hours- as requires DC to hold onto antigen or carry them back and become activated

Question 11

What are the two types of antigens/

Answer 11

T-cell dependent (TD)

T-cell independent (TI)

Question 12

Tell me about T-cell dependent (TD) antigens

Answer 12

T- cell dependent (TD)

Protein antigens, presented as peptides on MHC class II

Require direct contact with TH cells, not just exposure to TH cell-derived cytokines

Response involves GC formation, high affinity class-switched antibody and generates memory B cells

Question 13

Tell me about T-cell independent (TI) antigens

What are the two types?

Answer 13

T-cell independent (TI)- may still get some help from T-cells via cytokines as opposed via direct cell interactions

Carbohydrate/ lipid / (i.e., not protein)

Large with repeating structures

Interaction with a cognate T cell is not required

limited ability to class switch and to generate memory

The two types are: TI-1 and TI-2

Question 14

Tell me about TI-1 antigens

Answer 14

TI-1 antigens are non-specific stimulators of B cells and may be derived from bacterial cell wall components (e.g., LPS)

Question 15

Tell me about TI-2 antigens

Answer 15

TI-2 antigens have multiple repeating subunits and crosslink the BCR (e.g., polysaccharides from bacterial cell walls)

Question 16

Summarise the TI-2 immune response and some general features of it

Answer 16

general features;

• rapid antibody production
• IgG2
• No memory
• Unmutated antibody

Question 17

Summarise the TD immune response and some general features of it

Answer 17

general features:

• delayed antibody production
• extensive class switching
• memory
• high affinity antibody

This has high affinity antibodies and takes longer to go through the germinal centre response

Question 18

Activation of the adaptive immune response (3-14 days)

Answer 18

Question 19

Tell me about the basic timeline for the activation of B cells

Answer 19

Detect whole antigen using B cell receptor (membrane Ab)

• ~2 hours to process and present
• ~6 hours move to B-cell/T-cell boundary- where it can interact with CD4 TH
• Causes activation, proliferation, and differentiation
• Can receive ‘help’ from CD4 T cells

Question 20

How do B cells know which isotype to make?

Answer 20

Question 21

Can can get different antibody isotypes dependent on the location in the body

Answer 21

Question 22

What cells provide the ‘help’ to make antibodies?

Answer 22

CD4 T cells

Question 23

Tell me about the extrafollicular response

Answer 23

This response also has rapid antibody production

Question 24

Tell me what the paper by Roco et al immunology 2019 hypothesised about class switch recombination

Answer 24

Abstract

Class-switch recombination (CSR) is a DNA recombination process that replaces the immunoglobulin (Ig) constant region for the isotype that can best protect against the pathogen. Dysregulation of CSR can cause self-reactive BCRs and B cell lymphomas; understanding the timing and location of CSR is therefore important. Although CSR commences upon T cell priming, it is generally considered a hallmark of germinal centers (GCs). Here, we have used multiple approaches to show that CSR is triggered prior to differentiation into GC B cells or plasmablasts and is greatly diminished in GCs. Despite finding a small percentage of GC B cells expressing germline transcripts, phylogenetic trees of GC BCRs from secondary lymphoid organs revealed that the vast majority of CSR events occurred prior to the onset of somatic hypermutation. As such, we have demonstrated the existence of IgM-dominated GCs, which are unlikely to occur under the assumption of ongoing switching.

general point: That class switch recombination occurs before it enters the germinal centres as opposed to in the germinal centres like previously thought

Question 25

Activation of the adaptive immune response

Answer 25

Leave the T cell zone and enter follicle to form germinal centre * Affinity maturation through somatic hypermutation (SHM) * Proliferating B cells undergo SHM

Question 26

Tell me about **follicular dendritic cells (FDCs)** and what they are

Answer 26

not related to DCs that present antigen to T cells (**FDCs do not present antigens to T cells**) FDC are **MHC class II negative** (why they can’t present antigens to T-cells) and present 3D antigen to B cells via **immune complexes (IC)** held on their surface IC **bind through complement receptors or Fc receptors** on the surface of the FDC

Question 27

Tell me about the steps to the germinal centre (GC) reaction

Answer 27

1. Activation of B cells and migrate into germinal centre 2. B cell proliferation 3. Hypermutation of Ig V genes 4. B cell recognition of antigen on follicular dendritic cells; selection of high-affinity B cells 5. Death of B cells that do not bind antigen 6. Exit of high-affinity antibody- secreting and memory B cells

Question 28

What processes do B cells undergo in the light and dark B cell zones?

Answer 28

**The dark zone** is where maturing B cells undergo gene mutations that modify their antigen receptors – the molecules they produce to bind to foreign targets. The light zone selects the B cells that bind most tightly and specifically to the target **Light zone** B cells may undergo immunoglobulin class-switch recombination (CSR) before light zone–dark zone recirculation, whereas other cells switch and directly differentiate (not depicted).

Question 29

What do we understand now about B-cell memory? Tell me the steps to how a naïve B cell becomes memory cells (different isotypes?)

Answer 29

Question 30

Tell me the different proteins that drive the maturation of a naïve B cell into plasma B-cells and memory B-cells

Answer 30

PAX5 is a master regulator of B cell lineage Downregulation of PAX5 leads to upregulation of BLIMP-1 and XBP-1 which leads to rapid plasma differentiation (low affinity cells) Increase of BCL-6 leads to germinal centre B-cells Not sure what leads to the memory B-cells being produced The 4 above show what leads to plasma B-cells

Question 31

How are the levels of different T cells effected in the SARS-CoV2 disease?

Answer 31

Reduction in T regulator cells Increase in cytotoxic Tfh and CD4-CTLs There is also a negative correlation of antibody titre which shows how neutralising antibodies produced by the hose in response to infection

Question 32

What happens in the germinal centre if the suppression of cytotoxic TFH cells is blocked?

Answer 32

Question 33

Time course of normal immune response

Answer 33

Question 34

Tell me about the mucosa associated lymphoid tissues

Answer 34

* Extrafollicular response including CSR IgM to IgA also takes place * 2˚ lymphoid tissues being produced and germinal centre reactions occurring * Can get extrafollicular responses occurring and IgM --\> IgA (mucosa --\> intestine) **The mucosa-associated lymphoid tissue (MALT)**, also called mucosa-associated lymphatic tissue, is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body, such as the gastrointestinal tract, nasopharynx, thyroid, breast, lung, salivary glands, eye, and skin.

Question 35

Tell me about **IgA** * structure * where it's found * secretion amount and from where * how its exported

Answer 35

**Monomeric** IgA is found in the **blood, lymph and extravascular spaces** **Dimeric** IgA is found on **mucosal membranes and in secretions** * milk, saliva, tears, sweat, & mucus * 10-15 g of IgA is produced each day; most is secreted. Exported via **Transcytosis**

Question 36

Tell me about the exportation of IgA via **transcytosis**

Answer 36

* epithelial cells express a poly Ig receptor * binds dimeric IgA via the Fc region * facilitates secretion of IgA at mucosal surfaces

Question 37

Tell me about the different antibody isotypes (classes)

Answer 37

IgG IgM IgA IgE IgD

Question 38

Tell me about the isotype-specific effector functions of IgG

Answer 38

Question 39

Tell me about the isotype-specific effector functions of IgM

Answer 39

Question 40

Tell me about the isotype-specific effector functions of IgA

Answer 40

Question 41

Tell me about the isotype-specific effector functions of IgE

Answer 41

Question 42

Tell me about the isotype-specific effector functions of IgD

Answer 42

Question 43

What are the different sub-classes of the IgG antibody isotype?

Answer 43

IgG1 IgG2 IgG3 IgG4

Question 44

What are the different functions of the IgG antibody isotype sub-classes?

Answer 44

IgG is more potent than other isotypes at engaging effector functions **_There are four IgG sub-classes (human):_** **IgG1:** complement fixing, binds Fc receptors with high affinity **IgG2:** complement fixing, binds Fc receptors with low affinity- produced in T-cell independent type 2 reactions **IgG3:** complement fixing, binds Fc receptors with high affinity **IgG4**: not able to fix complement, binds Fc receptors with intermediate affinity **(Mouse: IgG1, IgG2a, IgG2b and IgG3) of note, the numbering does not correspond to the human sub-classes**

Question 45

A table summarising the functions of antibodies

Answer 45

Question 46

Fc receptors summary

Answer 46

Question 47

Tell me about the functions of neutralising antibodies What are the different functions they can do?

Answer 47

Neutralising antibodies can: 1. block the microbe and infection of cell 2. blocks the infection of adjacent cells 3. blocks binding of toxin to cellular receptor

Question 48

Tell me the steps to **opsonisation- antibody dependent cellular phagocytosis (ADCP)**

Answer 48

Question 49

Tell me about **antibody dependent cellular cytotoxicity (ADCC)**

Answer 49

Question 50

What spaces can IgG access?

Answer 50

extracellular spaces

Question 51

Tell me about **IgG**

Answer 51

smaller than IgM flexible arms Brambell receptor (FcRB) or Neonatal FcR (FcRn) expressed on endothelial cells and in the placenta

Question 52

Tell me about the levels of different Ig before and after birth

Answer 52

Question 53

Tell me about **MAbs** for cancer

Answer 53

1. Direct attack on cancer cells rituximab (anti-CD20, lymphoma herceptin (anti-Her2, breast and ovarian cancer), cetuximab (anti-EGFR, lung cancer) 2. Engage immunity (e.g., checkpoint inhibitors anti-CTLA4 and anti-PD1) used in melanoma, lung cancer and some other solid tumours 1) Direct attack on cancer cells rituximab (anti-CD20, lymphoma herceptin (anti-Her2, breast and ovarian cancer), cetuximab (anti-EGFR, lung cancer) 2) Engage immunity (e.g., checkpoint inhibitors anti-CTLA4 and anti-PD1) used in melanoma, lung cancer and some other solid tumours

Question 54

What are the principles of vaccination

Answer 54

* Passive immunisation * Active immunisation

Question 55

Whats a vaccination?

Answer 55

Deliberate induction of an adaptive (acquire) immune response to a pathogen by injecting a vaccine – a killed or attenuated form of the pathogen, its toxins or surface proteins

Question 56

Whats an immunisation?

Answer 56

Deliberate provocation of an adaptive (acquired) immune response by introducing antigen (typically in form of a vaccine) into the body.

Question 57

Whats the primary and secondary goal of vaccination?

Answer 57

**Primary goal –** Eradication of disease e.g., smallpox **Secondary goal –** Prevention of disease e.g., MMR and COVID

Question 58

Give examples of diseases that have caused complete and partial protection

Answer 58

**Complete protection –** lifelong immunity e.g., MMR **Partial protection –** require boosters e.g., tetanus (cannot pass tetanus on because it’s present in soil. Cannot protect via herd immunity)

Question 59

What do vaccinations establish?

Answer 59

Memory to specific pathogens via the generation of T and B cells

Question 60

What immune system do vaccine primarily target?

Answer 60

The adaptive immune system

Question 61

Tell me about the history of vaccination

Answer 61

* First attempt of vaccination 15th century smallpox variolation (crusts either inhaled or inserted into small cuts) in China and Turkey * 1718 Lady Mary Wortley Montagu attempted to vaccinate own children using variolation * 1798 Edward Jenner inoculated 8-year boy with cow pox. The child never developed smallpox. * Complete eradication of smallpox in 1977 * The only human disease that has been eradicated

Question 62

Tell me about some emerging infections

Answer 62

Emerging infections * Marburg virus 1967 * Ebola virus 1976 * Legionnaire’s disease 1976 * SarS-CoV 2002 * Mer-CoV 2012-2015 * Ebola 2014 * SarS-CoV2 2019-2020 (100 years after Spanish Flu)

Question 63

Human population growth

Answer 63

Question 64

Tell me about **passive immunisation**

Answer 64

**Passive immunisation** Administration of preformed antibody to a recipient for the prevention and amelioration of infectious disease (temporary protection)

Question 65

Tell me about **active immunisation**

Answer 65

**Active immunisation** Administration of all or part of a micro-organism or a modified product of that micro-organism (toxoid, purified antigen, antigen produced by genetic engineering), to evoke an immune response mimicking that of the natural infection, but will usually present little or no risk to the recipient

Question 66

Tell me about the following of passive vaccines... * Long or short lived * sources * How are they given

Answer 66

**_Passive vaccination- antibodies_** * Short lived – not permanent * Sources **Almost all blood or blood products** **Homologous pooled human antibody** **Homologous human hyperimmune globulin (Rabies, CMV)** **Heterologous hyperimmune serum (anti-toxin – produced in animals)** **Transplacental – important in infancy** * Given IM – contain Ab aggregates and other serum products Can activate complement if given IV – anaphylaxis

Question 67

The largest on-going ebola outbreak in West Africe since 2015, tell me about the virus and also the treatments for it?

Answer 67

**Virus** * Negative sense ssRNA virus * Lipid enveloped * causes haemorrhagic fever * **Treatments** * Passive immunisation: * Sera from convalescent people * ZMapp cocktail of monoclonal antibodies

Question 68

Tell me about some stages for rescuing plasma cells from patients for best anti-viral antibodies

Answer 68

Question 69

What are the two forms of active vaccination?

Answer 69

**Live attenuated** **Inactivated**

Question 70

Tell me about **live attenuated active vaccinations**

Answer 70

* Attenuated form of natural virus or bacterium * Must replicate to be effective * Immune response is similar to natural infection * Few doses needed- usually one * Can induce severe reactions * Need to be stored carefully

Question 71

Tell me about **inactivated active vaccines**

Answer 71

* Cannot replicate * Generally, not as effective as live vaccines * Require multiple doses * Mostly humoral (B cell-antibody) responses induced * Antibody titres reduced over time

Question 72

Tell me some general characteristics of active vaccinations and some examples for each type for viral and bacterial infections

Answer 72

**_Active vaccination- activating the adaptive_** * Long lived – similar to natural infection without risk of disease * Live attenuated **Viral e.g., MMR** **Bacterial e.g, BCG** * Inactivated **Viral e.g., Flu** **Bacterial e.g., DTaP** * Detoxified endotoxin (toxoid) e.g., tetanus

Question 73

Tell me about inativated viruses

Answer 73

Whole- entire organism used Split- detergent lysed Subunit/ recombinant/ polysaccharide/ conjugate- purification of most immunogenic antigens

Question 74

Tell me about the different types of vaccines

Answer 74

Question 75

What does vaccination induce?

Answer 75

**Induces** * Antibody * T-cell immunity * - T-helper cells Assist in development and maintenance of B and cytotoxic T cells - Cytotoxic T cells Kills infected cells * Both antibody and cytotoxic T cells can confer protection against pathogens

Question 76

Tell me about the different vaccines used for COVID and some general structures about each

Answer 76

Question 77

Tell me about the structure of SARS-CoV2

Answer 77

Question 78

Tell me about the phagocytosis of SARS-CoV2 and how the cells deal with it

Answer 78

1. binding and viral entre via membrane fusion or endocytosis 2. release of viral genome 3. translation of viral polymerase protein 4. RNA replication 5. Subgenomic (nested) transcription 6. Translation of viral structural proteins 7. S, E and M proteins combine with nucleocapsid 8. Formation of mature virion 9. Exocytosis

Question 79

What do a majority of vaccines have for COVID

Answer 79

Question 80

Tell me about RNA vaccines

Answer 80

Question 81

Tell me about Vector vaccines and their mechanism of action

Answer 81

1. **Viral entry**: receptor binding, fiber shedding, viral internalisation 2. **Endocytosis**: capsid disassembly, exposure of protein VI 3. **Escape from endosome**: capsid disassembly, endosomal escap via lytic activity of pVI 4. **Trafficking to nucleus**: cytoplasmic trafficking using microtubules, dynin and dynactin 5. **docking at nuclear pore complex:** capsid disassembly, DNA import, viral transgene expression

Question 82

Tell me about **subunit vaccines**

Answer 82

Rather than injecting a whole pathogen to trigger an immune response, subunit vaccines (sometimes called acellular vaccines) contain purified pieces of it, which have been specially selected for their ability to stimulate immune cells. Because these fragments are incapable of causing disease, subunit vaccines are considered very safe. There are several types: protein subunit vaccines contain specific isolated proteins from viral or bacterial pathogens; polysaccharide vaccines contain chains of sugar molecules (polysaccharides) found in the cell walls of some bacteria; conjugate subunit vaccines bind a polysaccharide chain to a carrier protein to try and boost the immune response. Only protein subunit vaccines are being developed against the virus that causes COVID-19. Other subunit vaccines are already in widespread use. Examples include the hepatitis B and acellular pertussis vaccines (protein subunit), the pneumococcal polysaccharide vaccine (polysaccharide), and the MenACWY vaccine, which contains polysaccharides from the surface of four types of the bacteria which causes meningococcal disease joined to diphtheria or tetanus toxoid (conjugate subunit).

Question 83

In 2008, Herald Zer Hausen was given the nobel prize in medicine for what discovery?

Answer 83

That HPV causes cervical cancer

Question 84

HOV types in ano-genital malignancies

Answer 84

Question 85

Other HPV related cancer oropharyngeal cancers

Answer 85

Question 86

Tell me about prophylactic vaccines

Answer 86

Prophylactic vaccines By speeding up the immune response, vaccines usually prevent the development of disease symptoms, or reduce their severity, in response to the pathogen.

Question 87

The HPV life cycle

Answer 87

Question 88

Are there any therapeutic anti-cancer vaccines?

Answer 88

Not yet

Question 89

**LO**

Answer 89

* **Describe the kinetics of the humoral immune response** * **Identify the key cell types and receptors involved in an humoral immune response** * **Describe the generation of class-switched, high-affinity antibody** * **Describe the different types of vaccine** * **Explain how vaccines induce protective immune responses**