immunology Flashcards
innate immunity
non specific
instinctive
does not depend on lymphocytes
adaptive immunity
specific
acquired
requires lymphocytes
antibodies
origin of blood cells
all haemopoietic cells derived from pluripotent stem cells
gives rise to two main lineages- myeloid and lymphoid
neutrophils
polymorphonuclear leukocyte
phagocytosis
2 intracellular granules:
-primary lysosomes (myeloperoxidase, muramidase, acid hydrolases and defensins)
-secondary granules (lactoferrin and lysozyme)
can kill microbes by secreting toxic substances (superoxides)
size=10-14 micro-metres
3-11,000 per mm3 blood (65%)
lifespan= 6hr-12days
expresses CD66b
monocytes
mononuclear leukocyte
phagocytosis and Ag presentation
differentiate into macrophages in tissues
size=14-24 micrometres
100-700/mm3 blood (5%)
lifespan=months
presents CD14
FC, complement receptors, PRR, TLR and mannose receptors
macrophages
‘Large eaters’
Reside in tissues, Lifespan – months/years e.g. Kupffer cells – liver, microglia - brain
Phagocytosis & Ag presentation
Main role – remove foreign (microbes) and self (dead/tumour cells) Have
lysosomes containing peroxidase (free radicals)
Have Fc, complement receptors also Scavenger, Toll-like and mannose
receptors – can bind all kinds of microbes
eosinophil
Polymorphonuclear leukocyte
Size = 10-14 micrometres
100-400 per mm3 blood (5%) Lifespan – 8-12d
express CD125
Mainly associated with parasitic infections and allergic reactions
Granules contain Major Basic Protein – potent toxin for helminth worms
Granules stain for acidic dyes (eosin)
MBP – activates neutrophils, induces histamine release from mast cells &
provokes bronchospasm
basophil
Polymorphonuclear leukocyte
Size= 10-12 micrometres
20-50 per mm3 blood (0.2%) Lifespan – 2d
Granules stain for basic dyes
Very similar to mast cells
Express high-affinity IgE receptors
Binding of IgE to receptor causes de-granulation releasing histamine –
main cause of allergic reactions
Mainly involved in immunity to parasitic infections and allergic reactions
mast cell
Size 10-14 micrometres
Only in tissues (precursor in blood)
Very similar to basophils
Express high-affinity IgE receptors
Binding of IgE to receptor causes de-granulation releasing histamine –
main cause of allergic reactions
Mainly involved in immunity to parasitic infections and allergic reactions
T cells
Mononuclear leukocyte
Size= 5-12 micrometres
300-1,500 per mm3 blood (10%)
Lifespan= hrs – yrs,
Mature in thymus (T) Express CD3 (T cell receptor complex)
Play major role in Adaptive Immunity
-Recognise peptide Ag displayed by Antigen Presenting Cells (APC)
4 main types
o T helper 1 (CD4 – ‘help’ immune response intracellular pathogens) (cell medicated)
o T helper 2 (CD4 – ‘help’ produce antibodies – extracellular pathogens) (humoral)
o Cytotoxic T cell (CD8 – can kill cells directly)
o T reg (FoxP3) – regulate immune responses ‘dampen’
Found in blood, lymph nodes and spleen
B cells
Mononuclear leukocyte
Size =5-12 micrometres
300-1,500 per mm3 blood (15%)
Lifespan= hrs to yrs,
mature in bone marrow (B)
Express CD19 + 20 (depends on maturity)
Play major role in Adaptive Immunity
- Recognise Ag displayed by Antigen Presenting Cells (APC)
- Express membrane bound antibody on cell surface
- Differentiate into plasma cells that make Antibodies
Found in blood, lymph nodes and spleen
Natural killer cells
Account for 15% of lymphocytes
Express CD56, Found in spleen/tissues
Look like ‘large granular lymphocytes’
NK cells recognise and kill:
o Virus infected cells
o Tumour cells
Kill by apoptosis – programmed cell death
soluble factors of the immune system
complement
antibodies
cytokines
chemokines
complement (C’)
group of around 20 serum proteins that need to be activated to be functional
antibodies
bind to antigens (Ag)
Immunoglobulin (Ig)= soluble and bind to B cells as part of B cell antigen receptor Glycoproteins 5 different classes: -IgG (1-4) -IgA (1&2) -IgM -IgE -IgD
antibody definition
protein produced in response to antigen
can only bind with antigen that induced its formation
antigen definition
molecule that reacts with preformed antibody and specific receptors on T and B cells
epitope definition
part of antigen that bind to antibody
affinity
measure of binding strength between epitope and antibody binding site
higher the affinity the better
antibody structure
antigen recognition:
- fab regions= variable in sequence
- bind different antigens specifically
antigen elimination:
- FC region= contant in sequence
- binds to complement, FC receptors on phagocytes, NK cells etc.
variable and constant regions are encoded by different exons
Multiple variable region exons in genome can recombine and mutate during B cell differentiation to give different antibody specificity
IgG
main class in serum and tissues (70-75%)
important in secondary/memory responses
crosses placenta
IgA
15% of Ig
80% of IgA is a monomer
predominant Ig in Mucous such as saliva, milk and genitourinary secretions (secretory IgA, protects mucosal surfaces)
IgD
present at low levels
1% of Ig
transmembrane monomeric form is present on mature B cells
IgE
around 0.05% of Ig
basophils and mast cells express IgE receptor so continually saturated with IgE
allergic and parasitic
IgM
10% of Ig
pentamer
mainly found in blood as too large to cross endothelium
mainly primary response
cytokines
proteins secreted by immune and non-immune cells
Interferons:
- induce state of antiviral resistance in uninfected cells
- alpha and beta are produced by virus infected cells
- gamma released by activated Th1 cells
Interleukins:
- over 30 types
- pro-inflammatory (IL1) or anti-inflammatory (IL10)
CSF:
- colony stimulating factors
- direct division and differentiation on bone marrow stem cells
chemokines
chemotactic cytokines
around 40 proteins that direct movement of leukocytes from blood stream into tissues
attract leukocytes to site of infection
features of innate immunity
primitive
does not depend on immune recognition
no long lasting memory
defences
physical and chemical barriers
phagocytic cells
serum proteins
physical and chemical barriers
anatomical barriers:
- epidermis and dermis
- sebum (skin secretes), pH 3-5
mucous membranes:
- saliva
- tears
- secretions entrap
- cilia
- commensal colonies
physiological:
- temperature (pyrexia)
- pH
- gastric acidity
- oxygen tension
sensing microbes
in blood: monocytes and neutrophils
in tissues: macrophages and dendritic cells
receptors involved= PRR and PAMP and TLR
complement proteins activation pathways:
- classical= antibody bound to microbe
- alternative= C’ binds to microbe
- lectin= activated by mannose binding lectin to microbe
extravasation
leukocyte migration across endothelium
diapedesis:
-process of neutrophils moving out of vascular system
diapedesis process
tethering and rolling:
- slow neutrophil down (CD15 and E-selectin)
- neutrophil senses and binds to chemokines
secondary adhesion:
-neutrophil becomes static via binding its integrins and adhesion molecules on endothelial cells
spreading:
-neutrophil changes shape
extravasation:
-it squeezes through gap junction in endothelial cells along chemotactic gradient to site of infection
phagocytosis
binding
engulfment
phagosome formation
lysosome formation (phagolysosome and digestion)
membrane disruption/fusion
antigen presentation of non-self antigens that have been degraded
mechanisms of killing
O2 dependent:
- reactive oxygen intermediates
- superoxides (O2) converted to H2O2 then OH free radical
- nitric oxide (NO) vasodilates and increases extravasation
O2 independent:
- enzymes
- proteins
- pH
inflammation accessory molecule
acute phase proteins
C reactive protein:
- serum protein produced by liver, binds to some bacterial cells walls (pneumococci)
- promotes opsonisation, binding to C1q and activating C’
mannose binding lectin
need for adaptive immunity
microbes evade innate immunity
intracellular viruses and bacteria and hide from innate immunity
need memory to specific antigen so it’s faster
cell mediated immunity
interplay between APCs (macrophages, dendritic cells, B cells) and T cells
requires:
- intimate cell-cell contact
- MHC
- intrinsic/endogenous antigens
- extrinsic/exogenous antigens
- recognition of self and non-self
T cells
only responds to presented antigens not soluble antigens
if they recognise self they are killed in foetal thymus
T cell receptors recognise foreign antigens
Major histocompatibility complex
display peptides from self or non-self proteins on cell surface
Ag is bound to MHC and T cell receptor recognises MHC and peptide
MHC I= all nucleated cells
MHC II= only on APC
T cell Ag recognition
involved co-stimulatory molecules
required for full activation
leads to division, differentiation, effector functions and memory
Tc (CD8) activation
CD8 and MHCI/peptide = Tc/CTL effector cell
forms proteolytic granules
kills cells by inducting apoptosis
Th1 (CD4) activation
APC presents Ag with MHCII to CD4 cell
stimulation with high levels of IL2 activates naive cells to TH1 cells
proliferate (clonal expansion)
recognises Ag on infected cells and secretes interferon gamma to stop viral spread
help B cells make antibodies
Humoral adaptive immunity (B cell activation)
express Ig (D or M)
can only make one antibody that will only bind to one epitope on one Ag
born with 10^9 immature B cells
Bcells that recognise self are killed in bone marrow
B cells presenting Ag to T cells
monomeric IgM or MigD bind to Ag
phagocytosis
peptide displaced on surface with MHCII
TCR of naive TH binds to MHCII
T helper cells
APC eats Ag and presents it to naive CD4+ Tcells (turn into Th2 cells)
Th2 cells bind to B cells that present Ag
now secrete cytokines (IL-4,5,10,13)
these cause B cells to divide (clonal expansion and differentiate into plasma cells or memory B cells)
Ab effector functions
specific secreted antibody may:
- neutralise toxin when binding
- increase opsonisation (phagocytosis)
- activate complement
patterns in pattern recognition
limited characteristics
gram +ve/-ve
dsRNA
CpG motifs
PRR family
secreted and circulating PRRs
cell-associated PRRs =more traditional
secreted and circulating PRRs
antimicrobial peptides secreted in lining fluids, from epithelia and phagocytes:
- defensins
- cathelicidin
lectins and collectins= proteins containing carbohydrate that find carbs or lipids in microbe walls:
- improve phagocytosis
- mannose binding lectin
- surfactant A and D
cell associated PRRs
receptors present on cell membrane or in the cytosol of cells
recognise a broad range of molecular patterns
Toll like receptors are main family
TLRs
polymorphisms in TLR4 affect endotoxin responsiveness
inflammatory pathways interferon pathways (viral infections)
nod-like receptors
rapidly expanding family of another 22 human proteins
detect intracellular microbial pathogens
detection of peptidoglycan, muramyl dipeptide etc.
best known = NOD1, 2, and NLRP3
NOD2
widespread expression
recognises muramyl dipeptide- breakdown product of peptidoglycan
activated inflammatory signalling pathways
nonfunctioning= crohns disease
hyper-functioning= blau syndrome
Rig like receptors
RIG-1 and MDA5- detect intracellular double stranded viral RNA and DNA
couple effectively to activation of interferon production, enabling antiviral response
homeostasis and PRRs
neutrophil numbers may be dependent on TLR4 signalling
induction of endotoxin tolerance in the newborn gut
maturation of normal immune system
maintain a balance with commensal organisms
damage recognition and PRRs
TLRs recognise a range of endogenous damage molecules
appearance of host molecules in unfamiliar contexts can activate TLRs
TLR signalling by cellular damage products activates immunity to initiate tissue repair and perhaps enhance local antimicrobial signalling
PRRs in adaptive immunity
activation of TLRs and PRRs drives cytokine production by APCs
increases likelihood of successful T cell activation
TLR4 agonists vaccine adjuvants
TLR7/8/9 adjuvants in development
natural passive immunisation
e.g. transfer of maternal antibodies across the placenta to developing foetus
or breast milk to baby
protects against:
- diphtheria
- tetanus
- rubella
- mumps
- polio
artificial passive immunisation
treatment with pooled normal human IgG or immunoserum against pathogens or toxins
anti-toxins
anti-venoms
vaccination
manipulating the immune system to generate a persistent protection against pathogens after mimicking natural infection
mobilise the appropriate arms of the immune system and generate immunological memory
achieve natural exposure without risk of actual infection
process of active immunisation
- engage the innate immune system
- triggers molecular fingerprints of infection (PAMP etc.)
- engage TLR
- activate specialist APCs
- engage the adaptive immune system by generating T and B memory cells and Th cells
- memory cells then circulate for years
- seconds response is therefore prompt and powerful: high levels and affinity of IgG
types of vaccine
live or inactivated whole organism
subunit (toxins, antigenic proteins or recombinant proteins)
peptides
DNA vaccine
engineered virus
whole organism
live attenuated pathogen
e.g. TB or polio
prolonged culture leads to adaption and a strain that has reduced virulence in humans
whole organism advantages
attenuated pathogen sets up transient infection
full natural immune response
memory response
prolonged and comprehensive protection
single immunisation required
whole organism disadvantages
immunocompromised patients may become infected
can occasionally revert to virulent form
whole inactivated pathogen
inactivation usually by chemical treatment (formaldehyde)
heat can alter conformation of target antigens
whole inactivated pathogen advantages/disadvantages
advantages:
- no risk of infection
- storage less critical
- wide range of antigenic components present so good immune response
disadvantages:
- tend to activate humoral response so no T cell involvement
- without transient infection the immune response is weak
- booster required (issue with compliance)
subunit vaccine 3 types
purified molecular components as immunogenic agents
- inactivated exotoxins
- capsular polysaccarides (Men C)
- recombinant microbial antigens
subunit vaccine advantages/disadvantages
advantages:
- safe, only parts of pathogen used
- no risk of infection
- easy to store and preserve
disadvantages:
- immune response is less powerful
- repeated vaccinations and adjuvants required
- consider genetic heterogeneity to the population
synthetic peptides
produce a peptide that includes immunodominant B cell epitopes and can stimulate T memory cell development
lack of knowledge, peptides can by stimulatory or suppressive, most B cell epitopes are conformational
DNA vaccines
transiently express genes from pathogens in host cells
generates immune response similar to infection
leads to T and B cell memory response
DNA vaccines advantages/disadvantages
advantages:
- safe
- no requirement for complex storage
- drug delivery can be simple and adaptable to widespread vaccination programs
disadvantages:
- DNA vaccines are likely to produce mild response and require subunit boosting
- no transient infection
recombinant vaccines
imitate effects of transient infection with pathogen byt using non-pathogenic organism
genes for major pathogen antigens are introduced into non-pathogen microorganisms
recombinant vector vaccine advantages/disadvantages
advantages:
- create ideal stimulus
- produce immunological memory
- flexible
- safe
disadvantages:
- require refrigeration
- can cause illness in compromised individuals
- immune response to virus in subjects can negate effectiveness
adjuvants
any substance added to a vaccine to stimulate the immune system
aluminium salts- form precipitates and potentiate opsonised phagocytosis
chemicals can cause inflammation
toxoids and killed organisms trigger immune system
the ideal vaccine
- safe
- induce suitable immune response
- generate T and B memory cells
- stable and easy to transport
- should not require repeated boosting
passive immunity
transfer of preformed antibodies
does not activate immunological memory so no long term protection
general features of tumour
express antigens that are recognised as foreign by the immune system
immune response frequently fails to prevent the growth of tumours
the immune system can be activated by external stimuli to effectively kill tumour cells and eradicate tumours
etiology of cancer
transformation of germline cells= inheritable cancers (<10%)
transformation of somatic cells= non-inheritable cells (>90%)
environmental factors= UV (skin cancer), chemicals (lung cancer), pathogens (HPV causes cervical cancer)
hallmarks of cancer
growth self sufficiency evade apoptosis ignore anti-proliferative signals limitless replication potential sustained angiogenesis invade tissues escape immune surveillance
tumour immunology
induce clinically effective anti-tumour immune responses that would discriminate between tumour cells and normal cells in cancer patients
cancer immunosurveillance
immune system can recognise and destroy nascent transformed cells, normal control
cancer immunoediting
tumours tend to be genetically unstable
immune system can ill and induce changes in the tumour resulting in tumour escape and recurrence
Tumour antigens
tumour specific antigen:
- only found on tumours
- as a result of point mutations or gene rearrangement
- derive from viral antigens
tumour associated antigens:
- found on both normal and tumour cells but are over-expressed on cancer cells
- developmental antigens which become depressed
- differentiation antigens are tissue specific
evidence for tumour immunity
spontaneous regression (melanoma, lymphoma)
regression of metastases after removal of primary tumour
infiltration of tumours by lymphocytes and macrophages
higher incidence of cancer after immunosuppression or immunodeficiency
immune responses to tumours
t lymphocytes
antibodies
NK cells
macrophages
evidence for escape (detectable tumours)
immune responses change tumours such that the tumours will no longer be seen by the immune system (tumour escape)
tumours change the immune responses by promoting immune suppressor cells (immune evasion)
cancer immunotherapy
how to kill tumour cells without killing normal cells?
to induce an immune response against the tumour that would discriminate between the tumour and normal cells (adaptive immunity)
active immunotherapy
vaccination:
- killed tumour vaccine
- purified tumour antigens
- DNA vaccines
- viral vectors
augmentation of host immunity to tumours with cytokines and co-stimulators
passive immunotherapy
adoptive cellular therapy
anti-tumour antibodies
cell-based therapy
cellular therapies can be used to activate a patients immune system to attack cancer
do not act directly on cancer cells but work systemically to activate immune system
dendritic cells and cancer treatment
found throughout body
detect and ‘chew up’ foreign proteins and then present parts of this on their surface
the blood of a cancer patient is collected and enriched to increased population of dendritic cells to make a DC vaccine
tumour hypoxia
hypoxia is prominent feature of malignant tumours
inability of blood supply to keep up with growing tumour cells
hypoxic tumour cells adapt to low oxygen
clinical indications related to allergy
skin- eczema, itching, redness
airways- excessive mucus production, bronchoconstriction
GI- abdominal bloating, vomiting, diarrhoea
anaphylaxis- airway, breathing, circulation
allergy
abnormal response to harmless foreign material
atopy= tendency to develop allergies
allergic disease
anaphylaxis asthma rhinitis (hay fever) dermatitis food allergy
pathogenesis
usually involves IgE
strong concordance in twin studies
mast, eosinophil and dendritic cells
epithelial cells
lymphocytes
fibroblasts
mediators= cytokines, chemokines, lipids, small molecules
IgE and allergy
average serum conc. = 0.3-100 micrograms/ml
may reach 1000 in atopic individuals
binding of IgE
one antibody binds to one receptor with high affinity
clustering causes signalling:
- receptor cross linking causes assembly of signalling complexes
- these are amplified causing cellular response
low affinity IgE receptors
expression= B and T cells, monocytes, eosinophils, platelets and neutrophils
function= regulation of IgE synthesis, triggering cytokine release by monocytes, APCs
high affinity IgE receptor expressing cells
mast cells, eosinophils and basophils are major cell types
involved in host defence
mast cells and allergy
IgE mediated immunity
heterogeneity
primary role in innate and acquired immunity
involved in many disease processes
development of mast cells
produced by specific cell lineage in bone marrow
characterised by requirement for c-kit protein ( cell surface receptor for stem cell factor)
immediate mast cell functions
histamine- arteriolar dilation, capillary leakage, induces bronchospasm
chemotactic factors= some cytokines, IL4, CSF
proteases= tryptase, chymase
proteoglycans
typically lead to eosinophil attraction and activation
mast cell functions (minutes)
lipid derived mediatiors:
- leukotrienes= capillary endothelial contraction with vascular leakage
- prostaglandin D2=potent induced of smooth muscle contraction
- platelet activating
mast cell functions (hours)
transcription/translation- cytokines (IL8,5,4,13 and RANTES)
mast cell derived cytokines promote Th2 response and can lead to B cell class switching
activators of mast cells
indirect activators via IgE:
- allergens
- prior sensitisation required
- bacterial/viral antigens
direct activators:
- cold/mechanical deformation
- aspirin, preservatives, latex, proteases
mast cells and parasitic infections
hookworms, pinworms, flukes
IL3,4,5,10
local mast cell activation by cross linkage of IgE leads to recruitment of eosinophils and macrophages
role of IgE in parasitic infections explains presence of atopic individuals within population
other cells and allergy
lymphocytes- Th2
dendritic cells- APC
neurones- coughing and sneezing
what makes an allergen
particulate delivery
presence of weak pathogen-associated molecular patterns (PAMP)
nasal/skin delivery as oral delivery desensitises
low doses needed
anaphylaxis
within minutes:
- ABCDE
- mast cell or basophil activation (IgE or direct activation, histamine elevated)
- CV (vasodilation, lowered BP, increased vascular permeability)
- resp (bronchial constriction, mucus)
- skin (rash and swelling)
within hours:
-GI (pain and vomiting)
asthma
narrowed airway by tightened muscles and thickened arterial walls
39 genes associated
allergens:
- house dust mites
- aspergillus
eosinophil influx to lungs
treatment= corticosteroids
treatment of allergy
- avoid allergens
- desensitisation
- prevent IgE production or interaction with receptor
- prevent mast cell activation
- inhibit mast cell products
desensitisation
immunotherapy:
-increasing doses of antigen
risks= 23% have moderate reactions, 3% have life threatening
limited use= atopic eczema, asthma have no benefits
used only for serious conditions
preventing IgE production
Th2 response can be suppressed:
- delivery of suppressive cytokines (IL12 and 18)
- blockade of cytokines
- mucosal delivery of allergens fused to cholera toxin subunits
anti-IgE therapy
effective for asthma
costs a lot, slight increase in cancer incidence, anaphylaxis
anti-cytokine antibodies
IL5 antibody- adults with severe asthma
CD25 and IL2 antibodies- mild improvement in symptoms
IL25 antibody- reduces Th2 cytokine production in mice
mast cell activation
mast cell stabilisers reduce mediator release
calcium channel blockers
beta2 agonists increase cAMP
mast cell products
histamine receptor (H1) -numerous target cells
leukotriene antagonists
-inhibit Th2 cell activation
tryptase inhibitors
-prevent airway smooth muscle activation
treatment of anaphylaxis
0.15/0.3mg of IM adrenaline (epinephrin)
beta 2 adrenergic receptor activity:
- bronchial dilation
- myocardial contraction
- inhibition of mast cell activation
alpha adrenergic receptor activity:
- peripheral vasoconstriction
- reduction of oedema
