MODULE 3 - JO'S LECTURES Flashcards
where do B cells develop?
in the bone marrow
where do B cells get activated?
in the spleen or lymph nodes by naked antigen via BCR
what are some of the things B cells can do?
secrete antibody
present antigen on MHCII to CD4 T cells to activate them
can class switch (first isotype IgM)
can undergo somatic hypermutation (increasing ab affinity)
undergo clonal expansion
can differentiate in antibody producing plasma cells
how does BCR signal activate B cells with no signalling component?
has closely associated signalling components which are the invariant molecules Ig-alpha and Ig-beta
these closely associate with membrane bound Ig (BCR) to transduce signal into B cell
what are the clinical reasons it is important to understand B cell activation?
in order to:
develop new cures for cancer (B cell malignancies like lymphoma and leukaemia)
develop new treatments for AI diseases
make new vaccines
what are kinases?
enzymes that phosphorylate themselves and other proteins
phosphorylation can generate binding sites for other proteins to allow signal to transmit along chain
what are phosphotases?
take phosphate off things stopping signal transduction
what is the first messenger in BCR signalling?
naked antigen
what does the BCR consist of?
cell surface Ig (with two light and two heavy chains) + invariant signalling proteins Igalpha and Igbeta
Igalpha and Igbeta are connected by a disulphide-link to make them a heterodimer
what does the BCR co-receptor do and what does it consist of?
CD21 - complement receptor 2; binds complement-coupled antigen
CD19 - augments signalling through BCR and also recruits PI3 kinase
B cell equivalent of CD4/CD8; decreases BCR signalling threshold by amplifying BCR signals allowing B cells to respond to low levels of antigen
also includes CD81 which trafficks CD19 to cell surface
how and why can BCRs move around on the cell surface?
on lipid rafts
clustering together all the molecules is necessary to send a good signal down (I think this is called receptor clustering)
this clustering/aggregation is usually caused by highly repetitive structures e.g. flagellin
what is an example of T cell independent antigen?
highly repetitive structures like polysaccharide
how can antigen which is typically T-cell-dependent activate a BCR without T cell help?
monovalent soluble antigen can cause the Src family kinase Lyn to ‘disturb’ the actin cytoskeleton which obscures phosphorylation sites and open the BCR allowing signal transduction
how can antigen-bound complement fragments trigger the BCR?
antigen-bound complement fragments like C3d or C3b can bind to CD21; the antigen binds to the antibody (membrane bound?) resulting in cross-linking
outline the main intracellular signalling pathway for the BCR?
tyrosine phosphorylation is main mechanism by which transmembrane receptors transduce signals
phosphotyrosine residues are recognised by proteins containing the phospho-dependent binding domain SH2
SH2 domain proteins can act to recruit other molecules as enzymes or as transcription factors
what are the main tyrosines responsible for BCR signal transduction?
ITIMs (immunoreceptor tyrosine-based inhibitory motifs)
ITAMs (immunoreceptor tyrosine-based activation motifs)
these are found on Igalpha and Igbeta
how do ITAMs get phosphorylated BCR?
Src family kinases Fyn, Blk and Lyn associate with Igalpha and Igbeta
when ligand binds BCR and receptor clustering occurs the kinases phosphorylate tyrosines in the ITAMs on Igalpha and Igbeta
this allows Syk (another Src family kinase) to come in and bind the ITAMs on Igbeta too thus activating Syk
what does the Src family kinase Syk do?
Syk has two SH2 domains and binds ITAMs on Igbeta
by binding to phosphorylated site Syk becomes activated
Syk then phosphorylates the scaffold protein BLNK which induces formation of a membrane-associated signalling complex called the signalsome
what does BLNK do?
has multiple sites for tyrosine phosphorylation
it recruits other SH2 domain proteins to form the multi-protein signalling complex called the signalsome
what are the three pathways that can be activated by BCR signal transduction?
PLCgamma2 pathway (main pathway)
PI3K pathway
ERK pathway
outline the PLCgamma2 pathway of BCR signalling?
activated by Bruton’s tyrosine kinase (Btk) which gets recruited to the signalsome
this activates PLCgamma2 which then hydrolyses PIP2 into IP3 and DAG
this leads to increased intracellular calcium which cause PKC to get activated
PKC has multiple functions but the main one is activate MAPkinases which leads to TF activation
PKC also activates IKK which turns of inhibitory signal to NFkappB thus activating? it/turning it on
calcium flux also leads to activation of calcineurin which activates the TF NFAT
activation of these TFs leads to increased B cell activation and maturation
outline the PI3K pathway of BCR signalling?
phosphorylation of CD19 co-receptor by LYN activates PI3K
this leads to PIP3 production which recruits BCR signalling components to the plasma membrane and activates them
AKT is the main mediator of PI3K pathway and it leads to activation of genes which regulate cell cycle and apoptosis (leads to inactivation genes involved in apoptosis)
AKT activation induces pro-survival genes through IKK and mTOR (controls cell growth and proliferation)
overall the PI3K pathway promotes B cell growth and survival
outline the ERK pathway of BCR signalling?
RAS activation leads to ERK phosphorylation and dimer formation which allows it to translocate across nucleus to induce proliferation, survival and differentiation promoting genes
ERK can also be activated by PLCgamma2 pathway
how is BCR signalling negatively regulated?
ITIM phosphorylation turns shit off
it recruits phosphotases that dephosphorylate adaptor proteins like BLNK and also activates cellular calcium releases impairing calcium mediated signalling
how is BCR signalling negatively regulated?
ITIM phosphorylation turns shit off
it recruits phosphotases that dephosphorylate adaptor proteins like BLNK and also activates cellular calcium releases impairing calcium mediated signalling
what are two key defects of B cell development and differentiation?
Bruton’s tyrosine kinase (Btk) deficiency
Igalpha deficiency (agammaglobulinaemia)
what is Bruton’s tyrosine kinase deficiency?
Bruton’s disease or X-linked agammaglobulinemia means there is low or no Igs in blood (all isotypes)
Btk gene on X chromosome so only males get it
Btk is a crucial component of the signalsome as it phosphorylates and activates PLCgamma2. If no Btk this means no B cell proliferation, activation or maturation
symptoms include frequent infections and delayed growth
treatment involves regular intravenous gamma globulin and prompt treatment of any cuts/infections
what is Igalpha deficiency?
Igalpha crucial signalling component of the BCR
agammaglobulinaemia
symptoms include frequent infections and delayed growth and treatment involves regular intravenous gamma globulin and prompt treatment of any cuts/infections
what are the four key phases of B cell development?
BCRs form in bone marrow and B cell precursors rearrange Ig genes
negative selection occurs in bone marrow, immature B cell bound to self Ag is removed
B cells migrate to periphery, mature B cells bound to foreign antigen get activated
activated B cells give rise to plasma and memory cells leading to antibody secretion and memory cells in bone marrow and lymphoid tissue
how do autoreactive B cells get a second chance?
light chain encoded by kappa and lambda so if you are autoreactive you get a second chance to express other genes
but if those are still self-reactive you die
what occurs during antigen independent B cell development?
this is the first part of B cell development in the bone marrow where you get generation of lymphocyte diversity through Ig gene rearrangement
the B cell precursors here are stem cell, then pro B cell and then pre B cell
what occurs during antigen dependent B cell development?
the second half of B cell development which involves immature B cell, mature B cell, germinal centre B cell, memory and plasma B cells
important things which happen here include somatic hypermutation and antibody class switching (these occur once mature B cell binds foreign antigen)
what the fuck is the germinal centre?
mostly composed of proliferating B cells and 10% antigen-specific T cells
is very dynamic - grows as immune response increases and shrinks and disappears once infection is cleared
germinal centres generally found in lymph node or spleen
why is it beneficial that IgM gets secreted in pentameric form?
IgM gets secreted very early on in infection so tends to have very low binding affinity for antigen as hasn’t undergone somatic hypermutation
so instead its avidity gets increased by having lots of antigen binding points
what is antibody class switching?
genes for different isotypes ordered from IgM, IgD, IgG, IgE and then IgA
cytokines can induce RNA transcript production in “switch regions” near the heavy chain segment they preferentially induce (switch regions located just ahead of isotope genes)
so basically excises DNA for that isotope allowing the next to be expressed
once this DNA excised B cell cannot go back to making that isotype
how do switch regions allow class switching?
switch region sequences cause formation of secondary DNA structures that promote pausing of RNA polymerase II and binding of activation-induced deaminase (AID) which then introduces DNA breaks
AID can only bind ssDNA (like where gene transcription is occurring and RNA poly II has been paused)
AID also only expressed in activated B cells (it gets upregulated on activation)
how does AID drive somatic hypermutation?
AID works by deamination of cytosine to uridine which causes the mismatch repair system to try repair this resulting in point mutations (somatic hypermutation) and the good ones which increase affinity are selected for (affinity maturation)
this occurs in the IgV (variable) regions which encode protein that binds antigen
how does AID drive class switching and how is this different to the way it drives somatic hypermutation?
AID deaminates switch region instead of IgV region which results in double stranded breaks
repair mechanism for ds breaks just excises out the affected area and any genes (for any isotope) within that get lost
this means that once this DNA is looped out you can’t get those genes back and express that class of Ig and the next class on will be expressed
so the excising of these ds breaks allows for class switch recombination and the expression of new classes of antibody
how do cytokines regulate class switching?
cytokines regulate the gene transcription of switch regions
e.g. IL-4 enhances gene expression of switch region ahead of IgE so AID will deaminase this one
prob coming from an antigen-specific T cell in the germinal centre
what genes are expressed in a naive B cell and what happens when you add LPS and IL-4 to it?
recombined VDJ region encoding variable genes and also constant genes encoded by Cmew and Cdelta (making IgM and IgD)
if you add LPS these genes get upregulated but if you add IL-4 too you start to see gene expression in switch regions preceding IgG1 and IgE
outline somatic hypermutation?
occurs after antigen-driven B cell activation as part of germinal centre response and after receiving T cell signals
involves the introduction of point mutations to rearranged V region genes, ones that increase antigen affinity outcompete the others
50% chance that B cell will acquire a mutation in antibody it encodes at each division
requires activation of AID which deaminated DNA leading to base pair mismatches, lesion repair induces mutations
doesn’t have the same sequences that pause RNA polymerase II as switch regions do, no-one knows how it occurs in IgV gene for somatic hypermutation
how do 3’ enhancers ensure AID recruitment is specific to the discussed regions?
3’ enhancers after C regions enable chromosomal looping and this forms transcriptional domains that control transcriptional levels enabling AID to bind
without the 3’ enhancers there is no somatic hypermutation or class switching
what antibody isotype is best at opsonisation?
IgG1
what antibody isotype is best at sensitisation of mast cells?
IgE
what antibody isotype is best at complement activation?
IgM
what are the key functions of antibody isotypes?
neutralisation
opsonisation
sensitisation of mast cells
complement activation
each isotype is good at some of these to varying extents i.e. they all have different roles
how are antibody isotypes distributed?
distribution varied as they go different places to exert function
only ones that get through to placenta are IgG isotypes
all are found in serum
what are the two cells which exhibit B cell memory?
plasma cells
memory B cells
what are the differences between short-lived and long-lived plasma cells?
short-lived plasma cells reside in the lymph node or spleen
long-lived plasma cells reside in the bone marrow where they receive survival signals from stromal cells so that they can last months. These are a source of long lasting high affinity class switched antibody
both are antibody factories
what are memory B cells?
arise from germinal centre reaction (occurs in lymph node or spleen) and have inherited the genetic changes from this meaning they express high-affinity antibody and have undergone antibody class switching
they express higher levels of MHCII and co-stimulatory molecules than naive B cells so that they are ready to interact with T cells
thye populate the spleen and lymph nodes and circulate through the blood and divide slowly if at all and express surface Ig but do not secrete antibody and quickly generate antibody producing plasma cells if they re-encounter antigen
most current vaccines rely on B cell memory
what are memory T cells?
long-lived cells which survive after the contraction of effector phase resulting in a higher precursor frequency
have different activation requirements making them much easier to activate and respond upon reinfection and this also means different cell surface proteins from naive and effector cells
cytokines IL-7 and IL-15 important for memory T cell survival as well as periodic contact with MHC-peptide
divide more frequently than naive T cells
why are memory T cells better than naive?
proliferate more than naive T cells and in response to lower amounts of antigen
require less co-stimulation for activation than naive cells
produce cytokine faster and retain their polarised phenotype
may be strategically positioned in the tissue where the pathogen is most likely to be re-encountered
compare and contrast central and effector memory T cells?
central memory - express lymph-node homing molecules, slower than effector memory cells to produce cytokine, generally found in secondary lymphoid tissues e.g. spleen, lymph-node
effector memory - lack lymph-node homing molecule expression, rapidly produce cytokine upon antigenic stimulation, generally found circulating blood and tissues (might pass through lymph-node briefly)
what were key discoveries made regarding memory T cells?
discovery that lymph node homing molecules CCR7 and CD62L are co-expressed on a subset of CD4 and CD8 memory T cells
discovery that Tem persist in tissue and are functionally superior to Tcm
discovery of Trm subset as after infection memory CD8+ cells remain in tissues after infection clears without recirculating
what are tissue resident memory T cells?
lack lymph-node homing molecule expression, express the integrin CD103 and CD69 (help them locate and stay in tissue)
do not recirculate in blood
rapidly produce cytokine upon antigenic stimulation
could provide a problem for vaccination efficacy
what T cells will you find in blood?
naive T cells
central memory cells (Tcm)
effector memory cells (Tem)
WON’T FIND RESIDENT MEMORY CELLS (Trm)
what T cells will you find in a secondary lymphoid organ such as a lymph-node?
naive T cells
central memory T cells (Tcm)
resident memory T cells (Trm)
effector memory T cells (Tem) BUT they will leave quickly as they don’t have the signals to be retained there
what T cells will you find in the tissues?
mostly resident memory T cells (Trm)
also some effector memory T cells (Tem)
won’t really find any Tcm
what can resident memory T cells do upon reinfection?
Trm when restimulated can release cytokines that:
- tell APCs to upregulate con stimulatory molecules and lymph node homing molecules (for quicker presentation)
- tell NK cells to upregulate granzyme expression
can also possibly proliferate and create new Trm cells
can also possibly directly lyse infected cells
what are the three models of memory T cell development and which one is correct?
linear model
progressive model
divergent model
there is good evidence that all of them exist
what is the linear model of memory T cell development?
memory cells develop directly from differentiated effector cells
evidence: adoptive transfer studies show CD4 and CD8 T cells develop into memory populations that retain similar functional polarisations to the effector cells
(adoptive transfer meaning the cells were taken from one mouse and put in another)
what is the progressive model of memory T cell development?
degree of activation dictates the fate of a cell ( i.e. effector or memory)
evidence: transcriptional profile analysis of naive, memory and effector CD8 T cells generated after vaccination suggest cumulative antigen stimulation drives naive T cells to differentiate into memory T cells, then into terminally differentiated effector T cells
basically low activation = memory cell which can later on become effector, high activation = effector cell and effectors are always terminally differentiated
what is the divergent model of memory T cell development?
T cells are destined to an effector or memory lineage due to asymmetric cell division
evidence: clustering of receptors and molecules at the immunological synapse causes uneven distribution of cell contents in daughter cells
so all the molecules move around on lipid rafts and so upon activation one end of cell has them all and the other has fuck all and the one with fuck all becomes memory cell
how do resident memory cells develop?
BAFT3+ expressing DCs drive development of precursors to resident memory cells
reactivated Tcm can also possibly be driven to become Trm (and Tem)
Trm get recruited into the tissue by IFN-gamma producing CD4 T cells and here they get signals to upregulate CD69 and CD103 which are the molecules that tell them to stay the fuck in their place
how do we know there is plasticity among memory T cells?
Tcm can be driven to become Tem or Trm
how do different subsets of memory T cell differ at the transcription factor level?
Tcm express TFs TC1 and KLF2 which drive expression of homing molecules CD62L and CCR7 and S1PR1 (allows it to leave lymph node) and also cytokine receptors
Tem express BLIMP-1 which downregulates the Tcm TFs and allows it to express S1PR1 so it too can leave the lymph node
Trm express the TFs HOBIT and NUR77 which downregulates expression of Tcm molecules and upregulates CD69 and CD103 which tells it to stay in the tissue
what is trained innate immunity?
monocyte recognises pathogen through PRR
this induces epigenetic heritable changes in monocytes which results in broadly specific (cause they don’t have antigen receptors) enhanced protection
innate cells not long-lived but you can get innate immune training occurring in precursors in bone marrow which are sustained and so their daughter cells inherit these changes making them better suited to fight pathogens
evidence: many vaccines have effects extending beyond targeted disease e.g. BCG vaccine significantly reduces infuse mortality
what is trained innate immunity?
monocyte recognises pathogen through PRR
this induces epigenetic heritable changes in monocytes which results in broadly specific (cause they don’t have antigen receptors) enhanced protection
innate cells not long-lived but you can get innate immune training occurring in precursors in bone marrow which are sustained and so their daughter cells inherit these changes making them better suited to fight pathogens
evidence: many vaccines have effects extending beyond targeted disease e.g. BCG vaccine significantly reduces infuse mortality
what is cowpox?
causes pustular lesions on skin
first thing someone vaccinated for on some random 8 year old using variolation (giving a small bit of infected matter to healthy individual to give small but controlled infection)
what does a vaccine do?
induces memory without causing disease
what are the five types of vaccine?
protein (subunit) + adjuvant
DNA (not used in humans) or RNA vaccines
virus vectors (adenovirus, modified vaccinia)
virus-like particles (VLP)
inactivated pathogens (killed or live but weakend)
what are the two routes of vaccination?
oral
by injection (intradermal or intramuscular)
what are the features of an effective vaccine?
safe
induces protection from pathogen
gives sustained protection
induces neutralising antibody (essential to prevent infection of irreplaceable cells like neurons)
induces protective T cells
practical considerations e.g. low cost, stability for transport etc.
what things need to be considered when designing a new vaccine?
the desired immune response
route of vaccination (think of Trm cells)
mode of delivery
type of vaccine (desired antigen and antigen form)
type of adjuvant
what are some improvements on the usual vaccine delivery method (shove a needle into you) and why are they improvements?
needle-free delivery (e.g. oral vaccination which can be good at inducing mucosal immune response)
dermal delivery (micro needles)
these are potentially safer, cheaper, more effective and more palatable to the public than intramuscular delivery
why is dermal delivery so effective?
there’s a shit load of APCs in our skin
what are the four types of dermal delivery?
transcutaneous (patch + pretreatment w microneedles or abrasion)
epidermal (microneedles, jet injectors)
intradermal (fine syringes, microinjection)
percutaneous (multiple-puncture with short needles)
what are the two forms of microneedles?
hollow
solid
outline the benefits of intradermal delivery?
easier administration
reduced risk of sharps injuries
easier disposal
potentially improves immunogenicity
finding better methods of vaccination is important as:
reduced dose and cost per course
increased availability of limited antigens
avoidance of adjuvants
what do mucosal delivery vaccines use?
virus-like particles
liposomes
synthetic polymers
lipids
attenuated organisms
what do mucosal delivery vaccines use?
virus-like particles
liposomes
synthetic polymers
lipids
attenuated organisms
why might mucosal delivery be better for vaccinating for respiratory disease?
resident memory cells
what are adjuvants?
TLR and NLR agonists including:
- alum (triggers inflammasome)
- MPL (TLR4 agonist)
or can be toxins like pertussis toxin (downregulates Treg activity)
some are better at inducing different type of responses than others - important to find right one
why is it important to induce the correct immune response through vaccination?
to prevent disasters like the FI-RSV vaccine disaster from occurring
what is bronchiolitis?
infants bronchiole walls swell and obstruct the airway
caused by RSV (respiratory syncytial virus) which is ssRNA and -ve sense genome
epidemics occur in winter and kill 1/1000 infected infants
what are the best recognised antigens on RSV?
fusion protein (F)
attachment protein (G)
what was the RSV vaccine disaster?
despite the inactivated RSV vaccine inducing high antibody titres, many vaccinees required hospitalisation upon viral exposure and 2 infants died
so basically the FI-RSV vaccine exacerbated disease
post mortem findings: extensive bronchopneumonia and moncytic and eosinophilic infiltration
why did the FI-RSV vaccine exacerbate disease?
virus was strong TLR4 activator
formalin inactivated virus in vaccine didn’t activate TLR4 so there wasn’t much antibody affinity maturation - vaccine produced low avidity antibody response
this was in conjunction with a strong CD4+ T cell response and no cytotoxic CD8+ T cell response which led to formation of antibody complexes which activated complement
complement and the CD4+ T cell response drove a huge but unsuccessful inflammatory response in the lungs
what are considered to be the big three disease requiring vaccines (prior to COVID)?
HIV
TB
Malaria
why is it difficult to create vaccines for the big three?
HIV - high glycosylation, low rate of natural immunity, prob requires CD8 T cell and neutralising antibody response which is difficult
TB - low rate of natural immunity, increasing IFN production does nothing
Malaria - natural immunity is short-lived
it is also difficult to find adequate animal models which mimic the infection in humans
overall to design a new vaccine what do you need to consider?
the desired immune response (safety)
route of infection
mode of delivery
type of vaccine (desired antigen and antigen form)
type of adjuvant
what is SARS-CoV-2?
causes COVID-19
mostly spread through respiratory aerosols
important features are:
spike protein (virus derived, needed to infect host cell by binding ACE2 receptor)
virus envelope (derived from host cell it buds out of)
nucleic acid (RNA) coated with protein
how does SARS-CoV-2 infect cells?
it must bind to the human cell surface protein ACE2 receptor using its spike protein
the virus then enters the cell and hijacks the cells machinery to reproduce making thousands of new viruses
how do antibodies stop SAR-CoV-2 from infecting cells?
antibodies that stop this are anti-spike antibody
they bind spike proteins on virus so it can no longer bind ACE2 receptor
how do T cells help fight SARS-CoV-2?
cytoxic T cells can lyse infected cells (virus inside uncoated so non-infectious)
how do T cells help B cells make antibody?
CD40-CD40L interaction between T and B cells important for augmenting B cell response where class switching and somatic hypermutation happens
cytokines produced by T cells direct B cells to correct antibody isotype they need to be producing
how do RNA vaccines prevent COVID-19?
contain lipid nanoparticles with mRNA inside encoding SARS-CoV-2 full length spike protein with two proline mutations that lock the spike trimer into a pre-fusion conformation
upon binding ACE2 (can also happen spontaneously) the normal spike trimer is cleaved and folds irreversibly into post-fusion conformation - no use making antibody for this conformation
these lipid nanoparticles move into the cell and the mRNA gets translated
cells begin making spike protein which gets presented to B cells which start making anti-spike antibody
when virus actually infects we ready with the right antibody
what is the adjuvant in the SARS-CoV-2 vaccine?
the antigen itself
what is immune-complex-based disease enhancement?
phenomenon when using inactivated virus vaccines where it induces inappropriate immune response making non-neutralising antibody which results in shit loads of inflammation
observed in vaccines against RSV, SARS, MERS, feline coronavirus
one way to prevent this can include using an adjuvant
what is antibody-mediated disease enhancement (ADE)?
occurs through non-neutralising antibody binding virus and being taken up by Fc receptors of phagocytic cells
so rather than preventing infection you end up inducing infection in phagocytic cells
what are the two incorrect immune responses that the covid vaccine had to be careful not to induce?
immune-complex-based disease enhancement
antibody-mediated disease enhancement (ADE)
what is the correct antibody response you want the covid vaccine to induce?
when you get neutralising antibody which prevents spike protein interacting with ACE2
what was the paper that looked into mucosal neutralising antibody for the SARS-CoV-2 vaccine?
wanted to determine if the intramuscular mRNA vaccine induced respiratory immunity as this is the first site of infection
wanted to find out if vaccination and/or natural infection induced mucosal neutralising antibodies and if these are protective
took blood and bronchoalveolar lavage (BAL) samples from unvaccinated, vaccinated and convalescents
measured antibodies and antibody efficacy
found that vaccination induced as much IgG in blood and BAL as infection, but not as much IgA in BAL as infection (so mucosal IgA response not great after vaccination)
also found that mucosal B and T cell responses not great after vaccination as showed less specificity for virus
also found that a heterologous prime-boost (using two vaccines) more effective than homologous price-boost, especially if different routes of administration for prime and boost
what vaccines did they look at in the paper and what ones did they find worked best at inducing mucosal response?
protein subunit vax
viral vector vax
mRNA vax
they found that best mucosal response induced by using mRNA prime (administered intramuscularly) with viral vector (Ad5-S vaccine encoding spike) boost (administered intranasally) and it induces mucosal neutralising antibody
what were some limitations of the study?
small sample size
people of same demographic
they detected mucosal response but no evidence that it actually helps
outline how the immune system changes as we age?
early on we only have maternal antibody (IgG can move across placenta or IgA in breastmilk) as immune system developing
as you get older the strength of your immune response increase
then drops off once you get very old well Th2 response strength tends to linger
what is immunosensescence and what are the. ain things it manifests in?
the gradual deterioration of immune system function as you age
this manifests in reduced ability to fight infection, reduced vaccine efficacy and reduced tumour clearance
what barriers get weaker as you age and what does this mean?
physical and chemical barriers (skin gets weaker and also dryer so less AM properties, mucosal barriers less effective)
this leads to increased incidence and severity of disease
this is also very clear in NZ with demographics around influenza and is why flu vax free for over 65
how do shingles and immunosenescence link?
shingles is the reactivation of varicella zoster virus presenting as a painful rash
can lead to postherpetic neuralgia, vision loss and hearing loss as well as secondary infections
reactivates in old age as immune system weakens so some old people get vaccinated for this, however vaccine less effective as person older
what drives immunosenescence?
NOT due to lack of immune cells but due to reduced diversity of adaptive immune cells
- reduced T and B cell diversity
- reduced proportion of naive cells
- oligo-clonal expansion of memory cells
oligo-clonal means restricted clonality (so less clones expanding with memory so less diverse TCRs and BCRs)
why is there a decreased T cell function in old people?
decreased number of naive T cells in older age
accumulation of CD8 T cells with limited TCR repertoire leading to memory inflation (associated with CMV)
increased proportion of memory T cells
why is there a decreased number of naive T cells in older age?
progressive decrease in thymic output (called thymic involution)
what is the memory inflation associated with CMV seropositivity?
because of CMV constantly reactivating your T cells keep getting restimulated so you end up with shitloads of T cells specific for CMV which takes away from your T cell response to other things
why do we end up with an increased proportion of memory T cells as we age?
virtual memory CD8 cells accumulate which are cells with a memory phenotype but are antigen-naive so not actually that functional
same happens with conventional T cells subsets
broadly, why are the immune systems of old people shit and what does this result in?
shit cause:
- decreased thymic output due to thymic involution
- more inflammatory cytokines produced
- stem cells biased to myeloid lineage over lymphoid
- decreased self-renewal and increased DNA damage
- decrease in naive cells and increase in virtual cells
- decrease DC maturation so decreased antigen presentation
results in:
- decreased immune protection
- decreased poly-function
- decreased proliferation
- decreased effector molecule expression and TF expression
why do we see decreased B cell function in old people?
inefficient memory B cell generation
impaired B cell development due to decrease in numbers of early B cell progenitors (cause of stem cell bias to myeloid) and decreased expression of B cell development genes
alterations in size and composition of BCR expression
what does decreased B cell function result in?
increased susceptibility to infection
decreased antibody response to vaccination
increased incidence of AI disease
how is there a decreased expression of B cell development genes in old cunts?
surrogate light chain (SLC) is important for expression of a full functional BCR
less pre B cells expressing SLC in old people leading to immature B cells
this is called decreased B cell genesis
how are age associated B cells shit in regard to TLR signalling?
they rely on TLR7 or TLR9 signals for formation and activation and don’t respond to BCR signalling alone
because they rely mostly on TLR signalling for formation they often are enriched for autoantibody specificities leading to increased incidence of AI disease
(think about how old cunts get rheumatoid arthritis)
what is inflammaging?
heterogenous exogenous and endogenous danger stimuli (PAMPs and DAMPs) interact with a limited repertoire of sensors (e.g. TLRs, NLRs)
this results in worse inflammatory responses such as inflammasome activation and type I IFN responses
what is the structure/components of mucosal barriers?
outer mucus layer (traps microorganisms)
inner mucus layer (lots of cells making AM peptides and IgA)
these layers protect the epithelial cells and also have their own commensal microbiota
outline immunity in the respiratory tract?
constant exposure to inhaled antigens and allergens and so a common site of infection
so it needs to be able to response to the bad bacteria and not the good and needs to avoid damage as its so important
trachea and bronchi are tolerogenic cause they don’t want to be responding to stuff
in the bronchioles however there are lots of immune cells
in the alveoli there are alveolar macrophages
how does ageing effect respiratory immunity?
in healthy individual there are type I and II pneumocytes which are important for gas exchange and ALF secretion
there is also lots of alveolar lining fluid (ALF) which protects with pH and AMPs and also preserves cells so they maintain function
however in an ageing individual the ALF is oxidised so less protective
what immune cells do we have in the lungs?
lots of innate immune cells in lungs and adaptive in draining lymph node - so APCs in the lung can present antigen to adaptive cells in lymph node upon infection and then they come into lung to exert their functions
also have Trms and Tems in lung
have Tcms and Tems in lymph node
what are innate lymphoid cells (ILCs)?
have no antigen receptors but respond to cytokines the same way CD4 T cell subsets do
ILC1 (th1) makes IFN-gamma and TNF for intracellular infections
ILC2 (th2) makes IL-4, 5, 9 and 13 for worm infections and can cause allergy
ILC3 (th17) makes IFN-gamma, TNF, IL-22, 17 for extracellular bacteria and is associated with chronic inflammation
cytotoxic ILCs are called NK cells! and they produce p/g, IFN gamma and TNF for viruses and cancers
outline immunity in the GI tract?
often exposed to food antigens and is a common site of infection as a result
needs to be able to respond to bad bacteria and not good
to do this it has a specialised structure to allow antigen sampling and local immune responses
outline the specialised structure of the GI tract?
gut has villi to increase surface area - these have crypts
crypts have paneth cells making AMPs and goblet cells making mucus which protects epithelia
also has peyers patches (secondary lymphoid tissue) which are packed with adaptive immune cells and sit under M cells
M cells allow adaptive immune cells to translocated through them for antigen sampling
there are also a lot of Tregs in the gut to control inflammation
this makes crypts the most sterile part of the gut
how is homeostasis between the good and bad bacteria maintained in the gut?
the good bacteria help with digestion and don’t need virulence factors cause don’t need to infect us to survive
so these have no DAMPs resulting in Treg activation through TGF-beta production leading to tolerance in the gut
the bad pathogenic bacteria need to infect us to survive so have DAMPs which PRRs recognise and activate DC’s which make pro-inflammatory cytokines (IL-6, 12 and 23) which cause an inflammatory response from T cells
paneth cells constitutively express AMPs, when would they upregulate this?
if bacteria not being killed by AMPs this will lead to more TLR and NLR signalling which causes paneth cells to upregulate AMP production
this helps keep things in check without too much inflammation occurring
what happens during antigen sampling?
M cells translocate antigen to adaptive immune cells sitting underneath them
if this activates APC, it travels to mesenteric lymph node (the draining lymph node for the gut) or activates B cells in peyers patches
B cells can then make IgA (following class switching) and move to the lumen of the gut to fuck shit up
what antibody is found in mucosal surfaces?
IgA
outline memory immunity in the gut?
Trm (especially CD8) are found in the gut non-lymphoid tissue
Tem can also move into the non-lymphoid tissue, blood and lymphoid organs
Tcm are in the lymphoid organs
there is plasticity among these memory T cells; BATF3+ expressing DC’s can reactivate Tcm and IFN-gamma producing CD4 T cells recruit them into the tissue where the Tcms upregulate CD69 and CD103
what is the effect of ageing on gut immunity?
old people get changes in gut microbial communities and decline in intestinal tissue function
this fuels inflammaging which further fucks up the host microbiome (vicious inflammatory cycle)
what is a good way of researching gut immunity and intestinal disease?
using intestinal organoids which are an in vitro model of the gut
