BMS2052 Study Guide - Midterm Guide: Molecular Virology, Polymerization, Septic Shock
4 May 2018
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PRE-MIDSEM CONTENT
Introduction – Lect 1
Colonisation does not equal infection.
Microbes in health and disease – Lect 2 & 3
Gram negative PG has links between D-ala
DAP (this is a direct link)
Gram positive PG has peptide-inter-bridges
between D-ala L-lys
Gram negative (pink) has thin PG, brauns
lipoprotein (binds to PG), LPS is the most
outer layer has an O-antigen (molecular
mimicry), core polysaccharide (-ve change
stabilises structure), lipid A (endotoxin –
causes septic shock)
Gram positive (purple) has thick PG, no outer
membrane, liptechoic acid (binds to
membrane) and technoic acids (neg charge),
has surface proteins
Capsules are made out of glycocalyx. Can
mediate biofilm formation.
Flagella are for swimming into mucus.
Monochondrous – single, amphicondrous –
both ends, perichondrous – all over, polar –
one end or the other.
Bacterial pathogenesis Lect 4, 5, & 6.
Normal flora are involved in fibre digestion,
produce vitamins B12 & K for RBC production.
Colonisation involves adhesion – mediated by
pili and fimbrae. Afimbrial adhesions
strengthen adhesion.
Invasion is mediated by invasins. Can be
mediated by the host in response to a
bacterial trigger = trigger mechanism. This is
inside-out. Eg the T3SS inject proteins
can directly cause actin polymerisation or
through Rho actin pol. This forms a
pseudopod that engulfs the bacteria. E.coli
injects Tir protein Tir binds to intimin on
the E.coli for adhesion.
Invasion can be from cell surface receptor
ligand interactions = zipper mechanism. This
is outside in. eg integrin and cadherin
interaction activated R Rho actin
polymerisation.
Upon phagocytosis the bacteria can be killed
by either oxygen dependent or independent
mechanisms.
Bacterial evasion of the immune system
production of catalyse and protease to inhibit
respiratory burst. (evasion of phagocytosis)
Bacteria are chemoheterotrophs. They need
iron they secrete high affinity iron-
chelators (siderophores) have
hydroxamates and catechols and express iron
capture proteins lactoferrin and
transferrin. Also use haemolysins.
Exotoxins are secreted and some can be
destroyed by heat. Include membrane
disrupting toxins, AB toxins (botulinum,
cholera, diphtheria and tetanus) and super
antigens which cross-link MHC 2 on APC and
TC).
Endotoxin – part of the cell (commonly in the
cell wall). Eg LPS, lipd A, brauns lipoprotein in
G-. Lipotechoic acid, PG in G+. stimulate the
release of Il-1 and TNF (pro-inflammatory)
Molecular virology and infection – lect 7, 8 &
9.
Viruses have two phases: virion (outside of
cell – will attach) and infected cell (replicates
fast, has no structure). Viruses cause a
cytopathic effect on cells rounding up,
lysis, swelling of nuclei, fused cells,
duplication of membranes).
Ebola and Marbug are filoviruses.
PCR is used for screening field samples.
Multiplication & Mass Spec is used for
unknown pathogen
Serological tools are used investigation
natural reservoirs look at how many
animals have Ab.
Virus isolation and culture is considered the
gold standard.
Influenza A (birds are the natural reservoir)
infections humans and is the source of
seasonal influenza and pandemics. B and C
mainly infect humans but do NOT cause
pandemics. HA is for binding. NA is for
release.
Antigenic drift – changes to the RNA
polymerase activity (these are minor changes)
and the reason why we need new vaccines
every year.
Antigenic shift is major changes gene re-
assortment.
The avian flu has an abnormal pathogenesis.
It has decrease in WBC an low lymphocyte
count.
Immunology – Lect 12, 13, 14, 15, 16.
Alternative: C3 is activated and binds to
pathogen surface.
Lectin: C3 is activated by mannose binding
lectin.
Classical: C3 activated by Ab (IgM/ IgG) bound
antibody.
PRR type 1 IFN response = IFNa and B.
These are antimicrobial and germline
encoded.
Leukocyte recruitment is stimulated by IL-1
and TNFa secretion (activate the endothelium
to increase adhesion molecules) rolling
integrin activation on the leukocyte by
chemokines stable adhesion migration
through endothelium.
Rig-like helicases are in the cytoplasm and
recognise viral dsRNA. Activation results in an
interferon and pro-inflamm cytokine
response.
NLR NLRP3 inflammasome = NLR + ASC
adaptor protein and protease caspase. The
inflammasome cleaves IL-1B (this req two
signals) the PRR pro IL-1B formation and
then inflammasome cleavage.
BCR: has 2L and 2H chains. TCR: alpha and
beta chain.
TCs work by clonal selection (3 signals)
1. Antigen + MHC
2. Costimulation (CD80/CD86 to CD28 on TC)
3. Cytokines to differentiate T to effector T
from DC.
MHC is highly polymorphic and polygenic.
Intracellular endogenous can be self or
viral goes through the proteasome TAP
ER (binding to MHC 1) trough the golgi
MHC1 presentation to CD8+.
Extracellular (endocytosis) endosome –
lysosomal degradation vesicle with MHC2,
Li (is present in the ER and ensures
endogenous antigen presentation) CLIP
which is removed by HLA-DM MHC2
presentation to CD4+.
Cross-presentation is shunting extracellular
(endogenous) from the MHC2 pathway across
to the proteasome pathway to be presented
in the MHC1 pathway.
Dendritic cells go from their quiescent/
immature stage (which are highly phagocytic
and low MHC2) to their activated/ mature
stage (increase MHC2 and low phagocytic
activity) from PRR activation.
IL-12 (from DC), IFNy (from NKC) TH1 for
microscopic intracellular: produces IFN-y
activates macrophages, IgG switching, help
CD8
IL-4 TH2 for helminth (extracellular): IL-4
to IgE, IL-5 to eosinophil.
IL-16, IL-1, IL-23, TGF-B TH17 for
microscopic extracellular: IL-17 to neutrophil,
IL-22 to epithelium.
The peak IgM response is at day 7. The peak
IgG response is at day 14.
Viral recognition is through TLR 3, 7, 9 and
RIG. These stimulate the pro-inflamm
cytokines and NF-kB. The Antiviral response is
Type I IFN (a and B) and TNFa and IL-12 (peak
at 2-3 days). NKC mediated killing and CD8.
Type I response works by inhibiting viral
protein synthesis, viral RNA will get degraded.
The inhibition of viral gene expression and
virion assembly. DC and NKC activation (good
as many viruses lack MHC1). Neutralising
antibodies are IgA in the mucus in IgG in the
blood. Note that IgM is low affinity cannot
neutralise.
Combatting extracellular bacteria is through
the humoral response, Th17 neutrophil
recruitment. Complement opsins.
Opsonisation also from IgG and C3b
particularly important for capsulated bacteria.
IgA and IgG can neutralise toxins (can also
vaccinate against toxins). Abs against pili
prevent adhesion.
Combatting intracellular microbes, cellular
response, Th1 and CD8 work together. Note
that you need both CD4 activation of
macrophages and CTls (approx. 50:50).
MUCOSAL IMMUNITY
Tolerance is induced through the presence of
commensal bacteria and local suppressive
cytokines (TGF-B). Immune DC gets Ag from
food/ commensals to mLN present to
naïve T. immature DC do not present
CD80/CD86 only weak co-stim induce
Treg. These recirculate and maintain
tolerance.
Active immunity is induced by active
microorganism through epithelial barrier
influx of commensals overcome these
homeostatic mechanism. Active DC can co-
stim as they have CD80/86 & secrete IL-12
get Th1 and Th17.
M-cells in epithelium take up antigen in the
lumen DC in LP draining LN IMM
response is necessary
Plasma cells in LP secrete IgA binds to
bacteria preventing interaction with the
epithelium.
Goblet cells secrete mucus prevent
interaction.
Paneth cells secrete defensins (anti-microbial
proteins).
Th17, ILC3 (Innate cells). Secrete Il-22 –
promotes epithelium turnover to maintain the
barrier.
Central tolerance is incomplete (an
evolutionary driver). Central tolerance is
when self-reactive lymphocytes are deleted
during development.
Peripheral tolerance prevents inappropriate
activation by: apoptosis, anergy (only signal
1), inhibitory receptors (CTLA4) and Tregs.
Dengue fever virus of the flavi virus. Is a
+sense RNA. Is transmitted through the aeses
mosquito. There are 4 antigenically distinct
serotypes. Primary infection occurs with one
serotype Ab can neutralise and only mild
disease.
Dengue haemorrhagic fever. Is deadly and
from a secondary infection with a different
serotype, cross-reactive. The increased viral
titre triggers PRR TLR3 and RIG causes a
cytokine storm. Leaky vasculature caused by
TNFa.
Strep pyogenes. Causes skin lesions 3% get
Rheumatic fever (autoimm). Is associated
with heart problems. The antibodies against
the strep pyogenes wall cross react with the
heart valves. get complement and
macrophages pro-inflammatory response.
This is an example of molecular mimicry.
How molecular mimicry breaks tolerance.
Self reactive lymphocytes escape deletion by
central tolerance. They cross-react with
pathogens and are associated with infection.
Activated self-reactive lymphocytes react with
self antigen leading to autoimm diseases.
Inflammatory bowl disease. (chrons disease
and ulcerative colitis note that these are
multifactorial). Phase 1: environment triggers
in susceptible host. Phase 2: acute intestinal
inflammation (innate from pro-inflamm
Document Summary
Microbes in health and disease lect 2 & 3. Gram negative pg has links between d-ala . Gram positive pg has peptide-inter-bridges between d-ala l-lys. Gram negative (pink) has thin pg, brauns lipoprotein (binds to pg), lps is the most outer layer has an o-antigen (molecular mimicry), core polysaccharide (-ve change stabilises structure), lipid a (endotoxin causes septic shock) Gram positive (purple) has thick pg, no outer membrane, liptechoic acid (binds to membrane) and technoic acids (neg charge), has surface proteins. Monochondrous single, amphicondrous both ends, perichondrous all over, polar one end or the other. Normal flora are involved in fibre digestion, produce vitamins b12 & k for rbc production. Colonisation involves adhesion mediated by pili and fimbrae. Can be mediated by the host in response to a bacterial trigger = trigger mechanism. Eg the t3ss inject proteins can directly cause actin polymerisation or through rho actin pol. This forms a pseudopod that engulfs the bacteria.
