immunology Flashcards
Why do we have an immune system
To protect against invasion by foreign organisms
What are the two types of immunity that we have
innate and adaptive
What is part of the innate immunity
Macrophages, granulocytes, NK cells, complement, physical barrier, ect.
What is part of the adaptive immunity
T and B cells
Compare innate and adaptive immunity
the response time of the adaptive immunity is day Vs hours of innate
Innate has a limited and fixed specificity while the adaptive is highly diverse, improves during the course of the response
the innate response to repeat infection is the same as the initial response while the adaptive response is more rapid
What is the first barrier to infection
Epithelial surfaces (mechanical protection) joined by tight junctions
What is the initial precursor to all cells in the immune system
The bone marrow: stem cells
What are the circulating cells in the blood divided into?
erythrocytes (red blood cells)
leukocytes (white blood cells)
classification of white blood cells (leukocytes)
Granular (eosinophils, basophils, neutrophils)
agranular (lymphocytes, monocytes)
What is a phagocyte
Type of cell that has the ability to ingest and sometimes digest foreign particles, such as bacteria, dust or dye.
what are the types of phagocytes in the immune system
(monocytes:) macrophages dendritic cells (neutrophils) Neutrophil
Difference between phagocyte macrophage/dendritic cells and neutrophils
Neutrophils are mostly short lived (60-70% of leukocytes) while macrophages/dendritic cells are long lived - can be fixed or migratory
What are the characteristics of inflammation
- redness or vessel dilation
- heat
- swelling
- pain
Describe the process that leads to inflammation
- bacteria trigger macrophages to release cytokines and chemokines
- vasodilation and increased vascular permeability cause redness, heat, and swelling (increased blood flow)
- inflammatory cells migrate into tissue, releasing inflammatory mediators that cause pain
what are the changes that occur to the local blood vessels during inflammation
- dilation of the blood vessel- increased blood flow
- changes in adhesion molecules- allows blood cells to ‘stick’
- increased permeability- blood cells can move into the tissue
How are pathogens recognised by phagocytes?
- the macrophage expresses receptors for many bacterial constituents= PAMPs (pathogen associated molecular pattern receptors).
- bacteria binding to macrophages receptors initiate the release of cytokines and small lipid mediators of inflammation
- macrophages engulf and digest bacteria to which they bind
What are PAMPs
example
Pathogen associated molecular pattern receptors - on macrophages
bind to receptors which result in the activation and secretion of inflammatory mediators
example Toll like receptors (TLR)
What are the different macrophages in the body
They are found all over-
microglia: phagocytose dying neurons
Alveolar macrophages: respond to local surface-acting stimuli e.g. Irritants, asbestos by cytokine release
Spleen macrophages: immune function. phagocytosis of naturally dying cells, clearance of particulate agents
kuppfer cells: Exposed to gut derived microbial products. Cannot mount a respiratory burst
joint: synovial A cells: responsible for cytokines in arthritis ..
What is Phagocytosis
It is the internalisation of particulate matter by cells
What are the 4 stages of phagocytosis
- Binding to surface receptors e.g. PAMP receptors
- Engulfment into vacuole/ phagosome
- Fusion of phagosome with lysosome
- killing and degradation of bacterium by lysozyme, proteases, acid hydrolases, free radicals.
Why don’t tattoos fade?
because long-lived macrophages take up colloidal ink by phagocytosis and endocytosis in situ. when they die, new macrophages move in to phagocytose the dead cells, resulting in a permanent colouration
What do macrophages secrete once activated?
a range of cytokines:
IL-1beta, TNF-alpha, IL-6, CXCL beta, IL-12
What secreted by macrophages can produce fever
IL-1, TNF- alpha and IL-6.
IL-6 function
Lymphocyte activation
increased antibody production
TNF-alpha function
aActivates vascular endothelium and increases vascular permeability, which leads to increased entry to igG, complement, and cells to tissues and increased fluid drainage to lymph nodes
IL-1 beta function
Activates vascular endothelium
activate lymphocytes
local tissue destruction
increased access of effector cells
What are neutrophils
They are the main line of defence against invading bacteria
belong to the innate immune system
Neutrophils structure
multi-lobed nucleus
granulated cytoplasm
stains with both acidic and basic dyes
phagocytic
In a normal adult how many neutrophils are produced?
1-3 10^10 / day from bone marrow
what is the primary function of neutrophils
Phagocytosis and killing of pathogens
First cells to bind to inflamed tissue
neutrophils
must leave bloodstream to gain access to tissues (extravasation)
How do the neutrophils and macrophages know where to go
chemotaxis (movement of an organism in response to a chemical stimulus).
They move up a gradient of attractive molecules towards the the source.
closer to source = high concentration of attractive molecules (chemokines)
What is the complement system
A set of plasma proteins (C1-C9) that act together as a defence against pathogens in extracellular spaces
What are the effector functions of complement
recruitment of inflammatory cells
killing of pathogens
coats microbes with molecules (opsonins) that enhances their phagocytosis.
What are the three ways that complement can bind bacteria
- classical pathway: Antigen: antibody complexes
- MB:lectin pathway: lectin binding to pathogens surface
- Alternative pathway: Pathogen surfaces
binding leads to complement activation–> effector functions
How are mast cells activated
FceRI are high affinity receptors for IgE on the surface of mast cells
when cross linked by allergen- antibody complexes, mast cells respond by degranulation
What are mast cells and Basophils primarily responsible for
type I (immediate) hypersensitivity ???
What do Mast cells release
granules containing histamine and active agents
what do Basophils do
promote allergic response and augment anti-parasitic immunity
What are NK cells
natural killer cells: they recognise infected cells or tumour cells and destroy them.
What to NK cells develop from where?
develop in the bone marrow from common lymphoid progenitor cells
How are NK cells different to T cells
They are larger with distinctive cytoplasmic granules
Describe the steps of NK cells encountering a normal cell
- MHC class I on normal cells is recognised by inhibitory receptors that inhibit signals from activating receptors
- NK cell does not kill the normal cell
MHC I acts as a inhibitory signal for NK cells
Describe the activation steps of NK cells
- ‘Missing’ or absent MHC class I cannot stimulate a negative signal. The NK cell is triggered by signals from activating receptors.
- Activated NK cells release granule contents, including apoptosis in the target cells.
NKC activated by the absence of MHC class I
What is NKC activation controlled by (summary)
The balance of signals from activating and inhibitory receptors
(absence of MHCI)
Describe the steps of Antibody dependent cell-mediated cytotoxicity (ADCC)
- Antibody binds antigens on the surface of target cells
- Fc receptors on NK cells recognise bound antibodies
- cross-linking of Fc receptors signals the NK cell to kill the target cell
- Target cell dies by Apoptosis.
Bound Antigens provide a +ve signal to the NKC to preform apoptosis
What are Fc receptors
FcERI- high affinity receptors for IgE on the surface of mast cells (cross link allergen antibodies: degranulation of antibodies)
Fc receptors on NKC recognise bound antibodies. Contribute to the protective function of the immune system.
What are Fc receptors
FcERI- high affinity receptors for IgE on the surface of mast cells (cross link allergen antibodies: degranulation of antibodies)
Fc receptors on NKC recognise bound antibodies attached to infected cells or invading pathogens. Contribute to the protective function of the immune system.
What cells form part of the adaptive immune system
T cells and B cells
What cells form part of the innate immune system
NKC, Mast cells, Macrophages, dendritic cells, neutrophils…
Not specific to individual pathogens, rely on signals on the surface.
What do B-cells recognise Vs T-cells
T-cells recognise processed antigen fragments when bound to MCH molecules= antigen presentation
= a combination of peptides and the MHC complex
B cells recognise intact antigens directly through antibody molecules
t cells= fragments of antigens
B-cells= intact antigens
MHC?
Major Histocompatibility complex
main function of MHC molecules is to bind antigens derived from pathogens and display them on the cell surface for recognition by T-cells
T-cell recognition
TCR recognises antigen presenting cell: right MCH complex with bound peptide.
Highly specific
MCH class I structure
peptide binds though middle in peptide-binding cleft- formed by 2 alpha helixes. another alpha helixe and beta 2 microglobulin form base
Where are the peptides derived from for class I Vs Class II MCH molecules
Bind peptides from different compartments
MHC I : peptides derived from intracellular proteins- brought to the surface of the cell- displayed on the MCH I molecule
short peptides
> tells immune system a lot about what’s going on inside the cell.
MHC II: peptides are derived from extracellular or vesicle proteins- brought inside the cell in vesicles + bind to MHC II
long peptides
Viral proteins tend to invoke HMC class…
I: intracellular proteins
Extracellular bacteria tend to invoke MCH Class..
II: extracellular or vesicle proteins
What cells respond to peptide bound MHC
T-cells
what cells respond to MHC I
CD8 T-cell
what cells respond to MHC II
CD4 T-Cells
Where do T cells and antigen carrying cells first meet?
Antigens from sites of infection reach lymph nodes via lymphatic system
What is a Naive T-cell?
T-cell that hasn’t been activated yet, it stays in blood and lymph
How does a T-cell get activated
via a specific signal and co-stimulation
requires two signals
Signal 1 and signal 2.
A naive T-Cell requires what to be activated
Signal 1 and 2 or else the cell will be silenced
An effector T-cell requires what to trigger effector function
Signal 1 (T-cell receptor engagement)
How do dendritic cells function in naive T-cell activation
- immature dendritic cells in the periphery continually sample antigens in the environment by phagocytosis, macropinocytosis and receptor mediated endocytosis
- Upon stimulation by ‘danger signals’ DCs stop antigen uptake, up regulate co-stimulatory molecules (signal 2) and migrate to the lymph nodes - express B7: B7 positive dendritic cells stimulate naive T-cells
Dendritic cells function to activate T-cells by providing signal 1 (MHC/ peptide) and signal 2 (B7).
Where are T-cells educated?
Thymus
What is the system that prevents T-cells from acting on ‘self’?
By testing the affinity of the TCR to self peptides
If they have a strong affinity, they are auto reactive thus by negative selection they are deleted.
Weak affinity: positive selection- cell survives
very weak affinity: death by neglect- cell is deleted.
What are the two major subsets of T-cells?
CD8 T-cells: recognise MCH I + peptide in all nucleated cells
CD4 T-cells: recognise MHC II + peptide in professional APC (antigen presenting cell) (dendritic cells)
How do CD8 T cells function
Cytotoxic T Lymphocytes (CTL)
kill virally infected cells
secrete cytokines
How do CD4 T-cells function
produce Helper T- cells
TH1: secrete cytokine which activate macrophages, assist cellular immunity
TH2: provide signals for B-cell maturation
TH17: involved in inflammation
Treg: suppress immune response
What are the mechanisms involved in CTL (CD8 + T cell) killing
- primary mechanism
TCR triggering leads to the directed secretion of preformed lytic granules (5 min)= target cell death - second mechanism
membrane expression of FAS LIGAND causes cross linking of FAS on the target cell and triggering of apoptosis
What are the two main proteins found in Lytic granules, what is their function?
What are lytic granules?
Preforin: polymerises to form a pore in the target cell membrane
Granzymes:
- at least three serine proteases
- activate apoptotic pathways in the cytoplasm of the target cell
Secreted by the CTL T cells in response to TCR triggering.
where do T cells develop
in the thymus
What is the function of CD4 + TH1 T cells
Secrete IFN-gamma, TNF- alpha to help macrophages.
The APC in tissues (dendritic cell become mature) express the two signals. activate CD4 T cell–> cause proliferation differentiation in lymph node and migration to inflammatory site—> TH1 connect to infected macrophage via signal 1–> activation of infected macrophage to kill intracellular pathogens
What is the function of CD4 + TH2 cells
Help for B cells (secrete IL-4, IL-5)
TH2 cells bind B cell, signal 1, release IL-4, iL-5: causes proliferation, differentiation Ig production, Ig class switching in B cell bound antigen.
Most antibody production is dependent on … help
T cell
The balance of CD4 T Cell TH1 Vs TH2 affects disease outcomes
example
mycobacterium leprae infection- two forms of disease depending on which is primary response TH1 or TH2.
TH1 response: macrophage activation- Tuberculoid leprosy (eradicated)
TH2 response: antibody release: lepromatous leprosy- proliferate out of control
lepromatous leprosy results from
mycobacterium leprae infection –> failed TH1 cells activation, thus fails to eradicate the disease
What are antibodies or immunoglobins (Ig)
glycoproteins found on surface of B-cells (as part of B cell receptor =BCR) and in mammalian serum and tissue fluid
What do antibodies recognise
‘epitope’ of an antigen (e.g. on pathogen)
each B-cell produces antibodies of a single specificity (recognise specific epitope of antigen)
What do antibodies / immunoglobins do
they recruit molecules and cells to destroy pathogens
What happens when antigen is recognised by BCR
The antibody must have same specificity as the membrane bound form.
B cells mature into antibody secreting = plasma cells
What is the antibody structure
draw + describe
4 upper sections (Fab) and two lower sections (Fc) joined to mirror sections by disulphide bonds
An antibody has two basic regions : a variable region (N terminus) and a constant region ( C terminus) (variable region is the top of the two upper sections)
Also has light chain (2 outside top) and heavy chain (inside top and all bottom)
Which past of the antigen is in contact with antigen
Variable region/ half light and half heavy chain
What are the proteolytic cleavage molecules of antibodies
papain and pepsin
Where does Papain cleave the antibody
at the disulphide bonds - one spot
Where does pepsin cleave the antibody
below the disulphide bond- multiple cleavage points
What are the primary 5 isotypes of antibodies
What changes
- IgG
- IgM
- IgD
- IgA1
- IgE
heavy chain
light chains are either kappa or lambda
What determines the class/ isotype of an antibody
The heavy chain
What multimer does IgM form
pentomeric structure-
5 basic IgM units linked
10 identical binding sides
linked by J chain
What multimer does IgA form
Dimeric IgA
2 basic units of antibodies linked
4 identical binding sites
linked by J chain
Where does B cell development occur
in the bone marrow
Describe the steps of B cell development
- B cell precursor rearranges its immunoglobulin genes- bone marrow stromal cell= generation of B cell receptors in the bone marrow
- Immature B cells bound to self cell- surface antigen is removed from the repertoire- negative selection in the bone marrow (testing step- ensure not autoimmune)
- mature B cell bound to foreign antigen is activated- B cells migrate to the peripheral Lymphoid organs
- activated B cells give rise to plasma cells and memory cells - Antibody secretion and memory cells in bone marrow and lymphoid tissue.
IgM is primarily involved in which part of an immune response
the initial part
Draw the antibody levels during an immune response
Antigen A introduced–> lag phase of 4 ish days –> primary response by IgM
Antigen A introduced again–> no lag response–> secondary response by IgG, IgA, IgE. (a lot more antibody in serum)
Describe Isotope switching
Switch from IgM production to other isotypes (IgG, IgA)
need the variable region- VDJ + elements to encode constant region.
genetic elements called switch elements loop out parts of the sequence. Realigns the variable region with a different element.
Directional process, can only happen downstream.
Switching the heavy chain- determines the isotype
- heavy chain
- light chain
- All constant elements
Variable region in heavy chain made of 3 regions: VDJ (variable diversity join) - body will randomly chose one section in each region. - variable region in light chain made from 2 regions: VJ
variable regions= where diversity comes in, so you can recognise numerous antigens
What mechanisms are responsible for antibody diversity
- Heritable V/D/J gene segments and somatic recombination
- Junctional diversity
- pairing of different heavy and light chains
- somatic hypermutation (not part of development- an enzyme will come in and try and increase affinity of antibody to antigen)
In a lymph node, what are the different sections
paracortical area= mostly t cells
Secondary lymphoid follicle with germinal centre (B cells)
Medullary cells= macrophages and plasma cells
????
What is required for B cell activation
2 mechanisms for antibody production
Signal 1 and 2
- T-cell dependent antibody production
antigen provides signal 1
signal two comes from helper T-cell (CD40, cytokines) - T- cell independent antibody production
> rare in nature
get signal 1 and 2 from antigen
What are the antibody effector functions
- Neutralisation (Fc independent). Bind antigen and block function e.g. prevent entry into cell, block toxicity.
- Opsonisation (coating of microbe with molecules to allow its destruction by phagocytes). Promotes phagocytosis of antibody coated pathogens
- Complement activation. Recruits/ activates phagocytes, directly kill pathogen, opsonisation.
- ADCC (antibody-dependent cell-mediated cytotoxicity). NK cells destroy coated cells
- Triggering of mast cells, basophils and activated eosinophils.
What are some features unique to IgM antibody isotype
main antibody in primary immune response
What are some features unique to IgG antibody isotype
Transport across the placenta
What are some features unique to IgE antibody isotype
Sensitisation of mast cells, involved in allergy
What are some features unique to IgA antibody isotype
transport across epithelium, main antibody found at mucosal sites and mucosal secretions
What are some features unique to IgD antibody isotype
No know functions
What do B-cells produce that are important for recognition of diverse array of foreign antigens
antibodies
What are the research uses of antibodies
- Polyclonal Antibodies
- Monoclonal Antibodies
- Antibodies made by phage display
Polyclonal Antibodies
Animal Immunised (antigen/ adjuvant), followed by boosters.
serum (containing complx mixture of antibodies) is collected.
Antibody can be affinity purified
Antibody is heterogeneous, limited supply, batch specific
Monoclonal Antibodies
Animal immunised as in polyclonal antibodies
spleen cells harvested and fused with myeloma cells
single cell clones screened for reactivity against antigen
unlimited supply of antibody with defined specificity
Antibodies made by phage display
cDNA libraries generated (PCR)- H and L Chains V regions
these are fused to bacteriophage coat protein
Bacteriophage library screened for reactivity to antigen
Other applications for antibodies???
- immunoflurorescence microsopy.
- immunoelectron microscopy
- immunoprecipitation
- immunohistochemistry
- immunoblotting
- flow cytometry
- purification of cells (magnetic beads)
What are the two major categories of immune deficiencies?
1. primary immune deficiency > may be hereditary or acquired > immune deficiency is the cause of the disease 2. secondary immune deficiency > result of another disease or condition
What is the difference between how primary and secondary immune deficiency are acquired?
Secondary is the result of another disease, primary causes a disease
What does primary immune deficiency involve? (like cause?
50% involve antibody deficiency
20% involve combined Ab and cell mediated immunity deficiency
18% involve phagocytic disorders
10% involve cell mediated immunity deficiency
2% involve complement deficiency
Give example of a primary immune deficiency + cause
X-linked hyper IgM syndrome, involved defective CD40 ligand, implies there are no isotope switching. so extracellular bacteria can get in?
what are Secondary immune deficiency disorders a consequence of
examples
consequence of another disease or condition, generating further complications
- burns
- leukaemia (malignant cells replace functional T and B cells)
- Chemotherapy
- deliberate immunosuppression of transplant recipient
- certain infections (e.g. HIV)
Draw the curve of HIV infection effect on: Antibodies against HIV HIV specific CTL infectious virus in plasma CD4
Antibodies against HIV- rise quickly in the first 8 weeks- 2 years then drop quickly 1 year before death
HIV specific CTL- rise quickly in the first 8 weeks to 2 years- drop a bit 2-12 years in
infectious virus in plasma- significant in the first 4 weeks-8weeks then drops as protective functions come in- rise steadily 2-3 years before it takes over
CD4- initial drop then gradual decrease before being under protective level
What causes allergic rhinitis, asthma, systemic anaphylaxis
type 1 hypersensitivity
immune reactant: IgE
antigen: Soluble antigen
effector mechanism: mast cell activation
Immune reactant in type 1 hypersensitivity
immune reactant: IgE
Effector mechanism in type 1 hypersensitivity
effector mechanism: mast cell activation
What causes some drug allergies (e.g. penicillin)
type 2 hypersensitivity
immune reactant: IgG
antigen: cell or matrix associated antigen
effector mechanism: complement, FcR+ cells (phagocytes, NK cells)
What causes chronic urticaria (antibody against FCeR1alpha)
type 2 hypersensitivity
immune reactant: IgG
antigen: cell- surface receptor
effector mechanism: antibody alters signalling
Immune reactant in type 2 hypersensitivity
IgG
Effector mechanism in type 2 hypersensitivity
complement, FcR+ cells (phagocytes, NK cells) or antibody alters signalling
what causes serum sickness, arthus reaction
type 3 hypersensitivity
immune reactant: IgG
antigen: soluble antigen
effector mechanism: Complement, phagocytes
Immune reactant in type 3 hypersensitivity
IgG
Immune reactant in type 4 hypersensitivity
Th1 cells, Th2 cells (ass. CD4)
CTL (ass. CD8)
what causes contact dermatitis
type 4 hypersensitivity
immune reactant: Th1
antigen: soluble antigen
effector mechanism: macrophage activation
What causes chronic asthma, chronic allergic rhinitis
type 4 hypersensitivity
immune reactant: Th2
antigen: soluble antigen
effector mechanism: IgE production, Eosinophil activation, mastocytosis
what can also cause contact dermatitis
type 4 hypersensitivity
immune reactant: CTL
antigen: cell associated antigen
effector mechanism: cytotoxicity
What occurs in type I hypersensitivity
IgE immune reactant and the allergen cause the mast cell to activate and release histamine and leukotrienes
What are some clinical tests for allergy
Skin prick test
skin path test - application of allergen
type 4 hypersensitivity is also known as
delayed type hypersensitivity (DTH)
what is different about type 4 hypersensitivity compared to the others
It is antibody independent- T cell mediated
reactions develop hours to days after contact with antigen
Describe the steps in a DTH reaction
= type 4 hypersensitivity over the course of 24-72 hours:
- Antigen is injected into subcutaneous tissue and processed by local antigen-presenting cell
- A Th1 effector cell recognises antigen and releases cytokines which act on vascular endothelium = recruitment of previously primed Th1 cells.
- Recruitment of phagocytes and plasma to site of antigen injection causes visible lesion = recruitment of phagocytes and inflammatory cells
What is autoimmunity
An induction of an immune response against ‘self’
may be organ-specific, localised or systemic
consequences may be minimal or lethal
What is Autoimmunity related to
the breakdown of tolerance
What are tolerance mechanisms
the mechanisms to prevent autoimmunity
- Central tolerance/ negative selection (thymus)
- Antigen segregation (physical barrier, no access)
- Peripheral anergy (no costimulation)
- regulatory T-Cells
- Cytokine deviation
- Clonal exhaustion (apoptosis of cells after continuous stimulation)
Examples of autoimmune diseases
organ specific
systemic
organ specific type I diabetes mellitus Goodpasture's syndrome Multiple sclerosis Grave's disease
systemic Rheumatoid arthritis scleroderma systemic lupus erythermatosus Primary Sjogren's syndrome polymyositis
Cause of cancer
the progressive growth of the progeny of a single transformed cell
transformation can be spontaneous, or as the result of exposure to certain viruses, ionising radiation or mutagenic chemicals
what is the theory of ‘immune surveillance’
proposes that the immune system continually surveys the body for the presence of abnormal cells, which are destroyed when recognised
also proposes that the immune system plays an important role in the regression of established tumours
What are the types of tumour antigens
- Mutated proteins
- re-expressed developmental antigens
- differentiation antigens (e.g. Tyrosinase)
- Over -expressed self antigens (e.g. Her2)
- Modified self antigens
- Oncoviral proteins (e.g. HPV)
What are the mechanisms by which tumours avoid immune recognition
- Low immunogenicity: immune system doesn’t realise. NO peptide: MHC ligand
no adhesion molecules
No co-stimulatory molecules - Tumour treated as self antigen: antigen but no co-stimulation (signal 2)
- Antigenic modulation: T-cells may eliminate tumours expressing immunogenic antigens, but not tumours that have lost such antigens. change antigens.
- Tumour induced immune suppression: factors secreted by tumour cells inhibit T cells directly, expression of PD-L1.
- Tumour induced privileged site: Factors secreted by tumour cell create a physical barrier to the immune system
What are some immunotherapies of tumours
- non-specific immune activating substances (e.g. adjuvant: stimulate APCs and NK cells)
- cytokine therapy (interferon for some leukaemia and carcinomas)
- monoclonal antibodies
- transfer of cytotoxic T- cells
- Vaccines (e.g. cervical cancer)
