B cell humoral immunity and vaccination Flashcards
LO
- 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
B cell immunity lecture 1 topics
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
Tell me the following features of the primary immune response
- Time lag after immunisation
- Peak response
- Antibody isotype
- Antibody affinity
- Induced by
- Required immunisation
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)
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
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
Why is the secondary immune response limited to protein antigens?
Requires new T-cell help and only needs low doses
This secondary response is dominted by IgG class switched antibodies
Tell me about the affinity and avidity of IgM and IgG antibodies
What are the general structures of each as well
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
What three different things help to traffick the antigen to the secondary lymphoid organs?
Roughly what size are each?
- Small soluble protien antigens (70kDa/ 5-6nm)
- Small particular antigens (20-200nm)
- Large particular antigens (200-500nm)
Tell me about small soluble protein antigens
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
Tell me about small particular antigens
- Enter lymphatic system via pores
- Passive drainage to lymphoid organs
- Transported into secondary lymphoid organs by myeloid or B cells
Tell me about large particular antigens
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
What are the two types of antigens/
T-cell dependent (TD)
T-cell independent (TI)
Tell me about T-cell dependent (TD) antigens
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
Tell me about T-cell independent (TI) antigens
What are the two types?
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
Tell me about TI-1 antigens
TI-1 antigens are non-specific stimulators of B cells and may be derived from bacterial cell wall components (e.g., LPS)
Tell me about TI-2 antigens
TI-2 antigens have multiple repeating subunits and crosslink the BCR (e.g., polysaccharides from bacterial cell walls)
Summarise the TI-2 immune response and some general features of it
general features;
- rapid antibody production
- IgG2
- No memory
- Unmutated antibody
Summarise the TD immune response and some general features of it
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
Activation of the adaptive immune response (3-14 days)
Tell me about the basic timeline for the activation of B cells
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
How do B cells know which isotype to make?
Can can get different antibody isotypes dependent on the location in the body
What cells provide the ‘help’ to make antibodies?
CD4 T cells
Tell me about the extrafollicular response
This response also has rapid antibody production
Tell me what the paper by Roco et al immunology 2019 hypothesised about class switch recombination
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
Activation of the adaptive immune response
Leave the T cell zone and enter follicle to form germinal centre
- Affinity maturation through somatic hypermutation (SHM)
- Proliferating B cells undergo SHM
Tell me about follicular dendritic cells (FDCs) and what they are
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
Tell me about the steps to the germinal centre (GC) reaction
- Activation of B cells and migrate into germinal centre
- B cell proliferation
- Hypermutation of Ig V genes
- B cell recognition of antigen on follicular dendritic cells; selection of high-affinity B cells
- Death of B cells that do not bind antigen
- Exit of high-affinity antibody- secreting and memory B cells
What processes do B cells undergo in the light and dark B cell zones?
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).
What do we understand now about B-cell memory?
Tell me the steps to how a naïve B cell becomes memory cells (different isotypes?)
Tell me the different proteins that drive the maturation of a naïve B cell into plasma B-cells and memory B-cells
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
How are the levels of different T cells effected in the SARS-CoV2 disease?
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
What happens in the germinal centre if the suppression of cytotoxic TFH cells is blocked?
Time course of normal immune response
Tell me about the mucosa associated lymphoid tissues
- 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.
Tell me about IgA
- structure
- where it’s found
- secretion amount and from where
- how its exported
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
Tell me about the exportation of IgA via transcytosis
- epithelial cells express a poly Ig receptor
- binds dimeric IgA via the Fc region
- facilitates secretion of IgA at mucosal surfaces
Tell me about the different antibody isotypes (classes)
IgG
IgM
IgA
IgE
IgD
Tell me about the isotype-specific effector functions of IgG
Tell me about the isotype-specific effector functions of IgM
Tell me about the isotype-specific effector functions of IgA
Tell me about the isotype-specific effector functions of IgE
Tell me about the isotype-specific effector functions of IgD
What are the different sub-classes of the IgG antibody isotype?
IgG1
IgG2
IgG3
IgG4
What are the different functions of the IgG antibody isotype sub-classes?
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
A table summarising the functions of antibodies
Fc receptors summary
Tell me about the functions of neutralising antibodies
What are the different functions they can do?
Neutralising antibodies can:
- block the microbe and infection of cell
- blocks the infection of adjacent cells
- blocks binding of toxin to cellular receptor
Tell me the steps to opsonisation- antibody dependent cellular phagocytosis (ADCP)
Tell me about antibody dependent cellular cytotoxicity (ADCC)
What spaces can IgG access?
extracellular spaces
Tell me about IgG
smaller than IgM
flexible arms
Brambell receptor (FcRB) or Neonatal FcR (FcRn) expressed on endothelial cells and in the placenta
Tell me about the levels of different Ig before and after birth
Tell me about MAbs for cancer
- Direct attack on cancer cells rituximab (anti-CD20, lymphoma herceptin (anti-Her2, breast and ovarian cancer), cetuximab (anti-EGFR, lung cancer)
- 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
What are the principles of vaccination
- Passive immunisation
- Active immunisation
Whats a vaccination?
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
Whats an immunisation?
Deliberate provocation of an adaptive (acquired) immune response by introducing antigen (typically in form of a vaccine) into the body.
Whats the primary and secondary goal of vaccination?
Primary goal – Eradication of disease e.g., smallpox
Secondary goal – Prevention of disease e.g., MMR and COVID
Give examples of diseases that have caused complete and partial protection
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)
What do vaccinations establish?
Memory to specific pathogens
via the generation of T and B cells
What immune system do vaccine primarily target?
The adaptive immune system
Tell me about the history of vaccination
- 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
Tell me about some emerging infections
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)
Human population growth
Tell me about passive immunisation
Passive immunisation
Administration of preformed antibody to a recipient for the prevention and amelioration of infectious disease (temporary protection)
Tell me about active immunisation
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
Tell me about the following of passive vaccines…
- Long or short lived
- sources
- How are they given
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
The largest on-going ebola outbreak in West Africe since 2015, tell me about the virus and also the treatments for it?
Virus
- Negative sense ssRNA virus
- Lipid enveloped
- causes haemorrhagic fever
- Treatments
- Passive immunisation:
- Sera from convalescent people
- ZMapp cocktail of monoclonal antibodies
Tell me about some stages for rescuing plasma cells from patients for best anti-viral antibodies
What are the two forms of active vaccination?
Live attenuated
Inactivated
Tell me about live attenuated active vaccinations
- 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
Tell me about inactivated active vaccines
- Cannot replicate
- Generally, not as effective as live vaccines
- Require multiple doses
- Mostly humoral (B cell-antibody) responses induced
- Antibody titres reduced over time
Tell me some general characteristics of active vaccinations and some examples for each type for viral and bacterial infections
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
Tell me about inativated viruses
Whole- entire organism used
Split- detergent lysed
Subunit/ recombinant/ polysaccharide/ conjugate- purification of most immunogenic antigens
Tell me about the different types of vaccines
What does vaccination induce?
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
Tell me about the different vaccines used for COVID and some general structures about each
Tell me about the structure of SARS-CoV2
Tell me about the phagocytosis of SARS-CoV2 and how the cells deal with it
- binding and viral entre via membrane fusion or endocytosis
- release of viral genome
- translation of viral polymerase protein
- RNA replication
- Subgenomic (nested) transcription
- Translation of viral structural proteins
- S, E and M proteins combine with nucleocapsid
- Formation of mature virion
- Exocytosis
What do a majority of vaccines have for COVID
Tell me about RNA vaccines
Tell me about Vector vaccines and their mechanism of action
- Viral entry: receptor binding, fiber shedding, viral internalisation
- Endocytosis: capsid disassembly, exposure of protein VI
- Escape from endosome: capsid disassembly, endosomal escap via lytic activity of pVI
- Trafficking to nucleus: cytoplasmic trafficking using microtubules, dynin and dynactin
- docking at nuclear pore complex: capsid disassembly, DNA import, viral transgene expression
Tell me about subunit vaccines
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).
In 2008, Herald Zer Hausen was given the nobel prize in medicine for what discovery?
That HPV causes cervical cancer
HOV types in ano-genital malignancies
Other HPV related cancer oropharyngeal cancers
Tell me about prophylactic vaccines
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.
The HPV life cycle
Are there any therapeutic anti-cancer vaccines?
Not yet
LO
- 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
