Immune System Flashcards
What are 5 organs of the immune system?
tonsils thymus spleen bone marrow lymph nodes
What is the purpose of the lymphatic system?
To move immune cells around the body to allow them to patrol for and watch out for pathogens
What are lymphocytes?
White blood cells that are patrolling through the immune system and the lymphatic system
What are the primary lymphoid organs?
Bone marrow
Thymus
What is the role of bone marrow as a lymphoid organ?
It provides a source of stem cells that develop into the ‘innate’ and ‘adaptive’ immune responses
What is the role of the thymus as a lymphoid organ?
It is the ‘school’ for white blood cells (T cells). The T cells learn how to recognise a pathogen and that they shouldn’t react to self.
If the T cells do not learn this, they are killed; only 10% survive
Circulate throughout the lymphatic system and patrol for pathogens
What are T cells?
Include CD4+ and CD8+ T cells. They are lymphocytes that arise in the bone marrow and fully develop in the thymus
What are the secondary lymphoid organs?
Spleen
Lymph nodes
Describe the lymph nodes
- small glands that filter lymph
- located along the lymphatic vessels
What are the three layers of defence of the immune system?
- chemical and physical barriers
- innate immunity
- adaptive immunity
What are the physical barriers that provide the first layer of defence of the immune system?
The skin and mucous membranes
Describe the skin
A physical barrier Epidermis: - dead cells - keratin - phagocytic immune cells (dendritic cells) - constant renewal Dermis: - thick layer of connective tissue - collagen - blood vessels - phagocytic immune cells
Describe how the dendritic cells work
They phagocytose pathogens and present their peptides to T cells
Describe the mucous membranes
A physical barrier
- 1 or 2 layers
- are made of an epithelium (tightly packed live cells)
- constantly renewed
- some of the cells are mucus-producing goblet cells that secrete a layer of mucus
Where are mucosal membranes?
They line parts of the body that lead to the outside and are exposed to the air
What is the role of mucus?
It contains enzymes and organisms that help trap and kill microbes
What are some of the protective chemicals produced by the skin and mucous membranes
- acid
- enzymes
- mucin
- defensins
- other chemicals
Explain how acid acts as a protective chemical (include the acid of the skin)
The acidity of the skin, vaginal and stomach secretions (the acid mantle) inhibits bacterial growth.
For the skin, sebum is produced in the sebaceous glands which are associated with hair follicles.
Explain how enzymes acts as a protective chemical (and give an example)
Lysozyme is an enzyme found in saliva, respiratory mucus, on the skin and lacrimal fluid of the eye and it destroys bacteria by breaking down bacterial cell wall.
Enzymes of the stomach also kill many different microorganisms.
Describe the mucociliary escalator
Finger-like projections called cilia beat in tandem to move the mucus up to the pharynx so if we inhale dust it will keep moving and we cough the dust up.
What are defensins and from what are they secreted?
they are antimicrobial peptides secreted by the mucus membranes and skin
Explain how skin defensins work
Form pores in the microbial cell membrane so if the microbe gets a pore in its membrane, it leeches out its membrane and dies
Explain how salt is an important chemical defence of the skin
Sweat glands to produce salty sweat
Salt is hypertonic so there is a greater concentration of solutes outside the cell then inside the bacterial cell so the bacterial cell starts leeching out its water and dehydrates so prevents bacterial survival and growth
What are the chemical defences of the skin?
Defensins
Lysozyme
Sebum (low pH)
Salt
What are 6 chemical defences of the mucosal surfaces?
Stomach (low pH) Gall bladder (bile) Digestive enzymes in the intestines Mucus Defensins Lysozymes in the tears and urine
What makes up the innate defenses?
The surface barriers (ie. the skin and mucous membranes) and the internal defences
What are 5 internal defences that make up the innate defences?
Phagocytes Natural killer cells Inflammation Antimicrobial membranes Fever
What makes up the adaptive defenses?
Humoral immunity (B cells) Cellular immunity (T cells)
Describe innate immunity
- are the cells already there?
- is it fixed?
- how fast is the response?
- what are some of the limitations of the innate immune system?
- the cells are already in place in the tissue
- rapid
- fixed
- limited specificities
- has no specific memory
Describe adaptive immunity (5)
- improves during the response
- slow to happen
- variable
- highly specific
- has memory
What is meant by innate immunity being fixed?
doesn’t change its specificity during the response
What is meant by innate immunity having limited specificities?
not good at telling one virus from another
What is meant by adaptive immunity being variable?
lots of different T and B cells so they can recognise lots of different things
What is meant by adaptive immunity being highly specific?
able to not only detect molecular components from a specific type of pathogen but it can also recognise a particular strain of a virus
What is meant by adaptive immunity having memory?
(able to recall when it has been exposed to a particular virus and if we encounter that virus again, you won’t get active disease)
How does the number of cell layers differ between the skin and mucous membrane?
The skin has many layers whereas the mucous membrane only has 1 or 2
Are the cells tightly packed in the skin or the mucous membrane?
Both
Are the cells dead or alive in the skin and the mucous membrane?
In the skin, the outer layer is dead but the inner layer is alive
In the mucous membrane, the cells are alive
Is mucus present in the skin or the mucous membrane?
mucous membrane
Are lysosomes and defensins present in the skin and the mucous membrane?
They are present in the skin
In the mucous membrane, it is present in some cases (urine and tears)
Is sebum present in the skin or the mucous membrane?
Skin
Is cilia present in the skin or the mucous membrane?
Only in the mucous membrane in the trachea and uterine tubes
What is blood made of?
Plasma (liquid) and formed elements
What makes up the plasma component of blood?
proteins (including antibodies and immunoglobulin)
other solutes
water
What makes up the formed elements of blood?
Platelets
WBC
RBC
What are WBC called?
leukocytes
Where do blood cells come from?
the bone marrow
Development of immune cells in the bone marrow is called
hematopoiesis
The stem cells in the bone marrow can form cells from what three blood lineages?
Erythroid
Myeloid
Lymphoid
The erythroid lineage is composed of what sort of cells?
Red blood cells (erythrocytes)
White blood cells are part of what two blood lineages?
Myeloid
Lymphoid
The myeloid lineage is composed of what sort of cells?
- granulocytes
- monocytes
- dendritic cells
- platelets (innate immune cells)
The lymphoid lineage is composed of what sort of cells?
- B lymphocytes
- T lymphocytes
Give an example of a granulocyte in the blood
Neutrophils
Describe the role of neutrophils
A type of granulocyte in the blood
- makes up 75% of the leukocytes
- highly phagocytic
- move through the blood and move into tissue during inflammation
Define phagocytic
“eat and kill” like vacuum cleaners of the immune system
Give an example of a granulocyte in the tissue
mast cells
Describe the role of mast cells
A type of granulocyte in the tissue
- line mucosal surfaces
- release granules that attract white blood cells to the area of tissue damage
What are two examples of phagocytic cells?
monocytes and macrophages
Describe the role of monocytes and macrophages and how they relate to each other
Monocytes are present in blood and have low phagocytosis. When they move into tissues (eg. spleen and liver), they differentiate into macrophages and here they have high phagocytosis
What are the two types of macrophages?
- resident (ie. ones that remain in the same tissues)
- migratory (ie. ones that move through the tissue)
What are the three important functions of macrophages?
- phagocytosis
- release of chemical messengers to other cells
- break up the things they have eaten and putting the molecules on their cell surface to show information about pathogenic microbes to T cells which links innate and adaptive immunity
What is the main role of dendritic cells?
Linking the adaptive and innate immune responses
Where are dendritic cells found?
They are found in low numbers in the blood and in all tissues in contact with the environment
Describe the role of dendritic cells
Usually one of the first cells to encounter phagocytose antigen. They migrate to lymph nodes where they present antigen fragments to T cells.
How do the cells of the immune system move around the body?
- cells are carried in the blood and the lymph
- cells can leave the blood to enter tissues when there is inflammation
- lymph in tissues collects in lymphatic vessels. These drain the lymph into the lymph nodes
- here the innate cells can interact with the adaptive cells and start an adaptive immune response
How do innate cells recognise pathogens?
by recognising PAMPs
What are PAMPs?
Pathogen-associated molecular patterns
What are some viral PAMPs?
- nucleic acid (ssRNA, dsRNA)
What are some bacterial PAMPs of the cell wall?
- lipopolysaccharide (LPS)
- endotoxins
- lipoteichoic acid
Describe how innate cells recognise pathogens
- on the wall of the cell, they have TLR
- when a PAMP binds to a receptor and the receptor recognises it, it send a signal down to the nucleus of the cell
- this signal regulates gene transcription so some genes start getting expressed at high level or low level
eg. more proteins of one type and less of others. - if the innate cell warns other cells that there is something going on, it would increase the gene expression of molecules that act as warning signals to other cells
Apart from on the cell surface, where else can TLRs be found?
Explain this process
- inside the cell in a phagolysosome (formed during phagocytosis)
- the nucleic acids of bacteria and viruses that get engulfed will be revealed and recognised by the PRRs
- if it recognises the DNA, it will send a signal to the nucleus to increase or decrease gene transcription
What are PRRs and what are they used for?
Pattern recognition receptors and they are used to recognise PAMPs
Give an example of a PRR
Toll-like receptors (TLR)
What is a fever?
abnormally hight temperature (>37`C)
What causes a fever?
When leukocytes and macrophages are exposed to foreign substances in the body, they release pyrogens (pyrogen interleukin-1 (IL-1)) which act on the body’s thermostat (in the hypothalamus) which raises the body temperature
How is normal temperature reestablished after a fever?
A decrease in the rate of phagocytosis reduces the amount of interleukin-1 released causes a decrease in the temperature
What is the purpose of a fever?
Stop the replication of pathogens and increase gene transcription in immune cells so there are more important molecules being produced
Describe the inflammatory response
- what happens what a foreign object enters the body?
- what how do neutrophils reach the site of infection?
- a foreign object enters the body
- chemical signals from tissue cells attract more cells by making a chemical gradient
- neutrophils detect the chemical gradient and enter the blood from the bone marrow
- neutrophils cling to the capillary wall
- the chemical signals from tissue cells dilate blood vessels and make capillaries leakier
- neutrophils squeeze through the leaky capillary wall and follow the chemical trail to the injury site
Why do we have red inflammation?
because the blood vessels have dilated
Why do we have swelling?
because the capillaries are leaky
Why is inflammation hot?
because the increased blood flow makes heat
Describe the five stages of phagocytosis
- the phagocyte adheres to pathogens or debris
- phagocyte forms a pseudopod that wraps around the phagocyte to eventually engulf the particle, forming a phagosome
- a lysosome binds with the phagosome to form a phagolysosome
- the acidic and toxic contents of the lysosome destroy the pathogens
- sometimes the vesicle removes indigestible and residual material via exocytosis
What happens in the phagolysosome?
- The TLRs recognise contents of bacterium
- the cell regulates transcription of a gene such as to make pyrogen for fever and down-regulates other things
- when the contents are broken down, they can be shown to the adaptive arm of the immune system
What is in the phagolysosome that kills pathogens?
- the low pH
- toxins such as H2O2 and NO
- enzymes such as proteases, lipases, nucleases
What does a protease do?
breaks down proteins
What do lipases do?
break down fats
What do nucleases do?
break down the DNA and RNA
What is the complement cascade?
a series of proteins activated in a sequence, each step catalysing the next. The purpose of the cascade is to release inflammatory chemicals that amplify virtually all aspects of the inflammatory process.
What are the three complement pathways?
- classical
- alternative
- lectin
Describe the classical complement pathway
antibodies can bind to pathogens and also to complement which triggers the first enzymatic reaction to start
Describe the alternative complement pathway
this is triggered when our complement system recognises proteins on the surface of microbes
Describe the lectin pathway
this involves lectins binding to specific sugars (mannose) on the surface of microorganisms and beginning the enzyme activity
Complement activation by any of the three pathways involves a cascade in which proteins are activated in an orderly sequence - each step catalysing the next. The three pathways converge at C3 which splits into…….?
C3a
C3b
Describe opsonisation
coating a microbe with antibodies and/or complement fragment C3b which enhances phagocytosis
What does recruiting involve?
C3a and C5a stimulate histamine release which causes inflammation and attracts phagocytes by chemotaxis
What are the three outcomes of the complement cascade?
- opsonisation
- lysis
- recruiting via chemotaxis
What is the role of C3a and C5a
Recruiting via chemotaxis
How does lysis occur and what causes it?
C3b activates complex components (C5b and C6-9) which forms a membrane attack complex (MAC). This is inserted into the cell’s membrane. MAC forms and stabilises a hole in the membrane that allows a massive influx of water, lysing the target cell.
Briefly describe how the adaptive immune system is initiated after microbes enter the body
- dendrites phagocytose the microbe
- they display the fragments of the microbe on the surface
- migrate from organs to the lymph nodes and present peptides on MHC to T cells to warn them that something is wrong
- effector arms get enabled (antibodies and killer T cells) to start the adaptive immune system
What are antigen presenting cells (APC)?
They are cells that engulf antigens and then present fragments of them on their own surfaces where T cells recognise them.
Give an example of a APC
Dendritic cells
What are two T cells that the peptide fragments are presented to?
CD4
CD8
What happening when CD4 is activated?
It releases cytokines which activates CD8 to become toxic and it stimulates the B cells to produce antogen
What happens when CD8 is activated?
They become cytotoxic (cytotoxic T lymphocytes- CTLs) which kills the virus infected cells
What is an antigen?
Anything that has the potential to be recognised by the immune system
Antigens can be
foreign or auto (self) antigens
What is a foreign antigen?
Anything from the outside
What is an auto (self) antigen?
The bodies own cells that the immune system recognises as an antigen - these are recognised in autoimmune disorders
What is the purpose of antigen uptake?
- Clearance of pathogens (innate response)
- For presentation to T cells (adaptive response)
When did the adaptive immune system evolve?
500 million years ago
Adaptive immunity is a feature of what sort of organisms?
vertebrates
Invertebrates have
innate immunity only
vertebrates have
both innate and adaptive systems
What is the advantage of adaptive immunity?
It keeps an imprinted memory of the pathogen
What are the two types of MHC?
MHC-| and MHC-||
MHC-| presents _________ antigens and is expressed on ________ _________ cells
endogenous (intracellular)
all nucleated cells
MHC-|| presents _________ antigens and is expressed on ________ _________ cells
exogenous (extracelular)
antigen presenting cells
Dendritic cells have what sort of MHC receptor?
MHC-|| receptor
Describe MHC-| antigen processing
- antigenic proteins of a cytoplasmic antigen are degraded into peptides in the cytoplasm
- peptides are imported to the endoplasmic reticulum
- peptide loading of MHC-| takes place in ER
- the peptides are expressed in the MHC on the cell surface
Describe MHC-|| antigen processing
- there is phagocytosis of exogenous antigen
- antigenic proteins are degraded in the acidic phagolysosome
- peptide loading of MHC-|| take place in the phagolysosome
- the peptides are expressed in the MHC on the cell surface
Where does peptide loading of MHC-|| take place?
the phagolysosome
Where does peptide loading of MHC-| take place?
the endoplasmic reticulum
What is lymph?
the clear fluid that circulates through the lymphatic system.
Where are T cells developed?
they developed from stem cells in the bone marrow
Why do T cells travel to the thymus?
Here they learn how to respond appropriately to an antigen.
There is also gene arrangement in the thymus
What two co-receptors can T cels express?
CD4 or CD8
Describe the process of gene rearrangement of the T cells in the thymus
Immature T cells randomly rearrange the ‘variable’ parts of their TCR gene in the thymus which ensures that the individual T cells are unique in terms of their TCR. This creates diversity in the T cell repertoire.
What does TCR stand for?
T cell receptor
Where is the variable region of the TCR gene?
the upper tip of the TCR which interacts with the MHC-peptide complex
T cells express ________ with ____________
T cell receptors (TCR)
co-receptors (CD4 or CD8)
T cells that have not been activated by MHC-peptide complex are
naïve
What are naïve T cells?
T cells that have not been activated by MHC-peptide complex
Experienced T cells that have been activated are
Effector T cells
What are effector T cells?
Experienced T cells that have been activated
The CD4 T cell is also called a
helper cell
Outline the role of the CD4 T helper cell
- recognises MHC-||-peptide complex
- helps CD8 T cell become cytotoxic
- helps the B cell make antibodies
Where are CD4 T cells located?
In the lymph nodes, spleen and are the first to interact with the dendritic cells
Outline the role of the CD8 T cell
- recognises the MHC-|- peptide
- develops into CTL
What does CTL stand for?
cytotoxic T lymphocyte (CTL)
What is the role of a CTL?
to kill other mammalian cells which is good for dealing with virus infected cells and cancerous cells
How do CD4 T cells help CD8 T cells become cytotoxic?
By releasing cytokines that activate CD8 T cells
Once activated, how do the CD8 cells (now CTLs) kill other cells?
They release cytotoxin granules which alert the mammalian cell to die
The cell death that CD8 instructs is called
apoposis
How do the CTLs know which mammalian cells to kill?
The virally infected cells have MHC-| receptors with peptides presented on their surface and the TCR of the CTL binds to it
As well as the formation of effector cells, T cells activation results in the formation of
memory T cells
What are memory T cells?
Long-lived T cells that respond vigorously to a second encounter of antigens
HIV infection causes what to happen to the CD4 T cells?
They deplete and they drop below the critical threshold. HIV stops CD4 from making antibodies via the B cells and making the CD8 cells cytotoxic
Where do B cells orginate?
In the bone marrow
What do B cells express?
Unique antigen receptors
- either BCR
- secreted antibody
What are plasma cells?
Activated B cells that secrete antibody
Where do B cells develop/mature?
In the bone marrow
Naïve B cells have what sort of antigen receptor?
BCR (B cell receptor)
Describe the BCR
- two identical heavy chains
- two identical light chains
Diversity of the BCR results from
Random genetic rearrangement so that the part in contact with the antigen is unique
Do the heavy chains or light chains contribute to antigen binding?
Both of them
Where are BCR located, and why?
They are embedded into the membrane so that the can signal into the cell when the antigen binds
What are the three functions of antibody?
- Neutralisation
- Opsonisation
- Complement activation
What is antibody neutralisation?
The blocking of a pathogen or toxogenic products from affecting our host cells.
What is antibody opsonisation?
Covering a pathogen in antibodies to make it “tastier” for the phagocyte. The phagocytes have receptors for the antibodies which allow the phagocyte to take it up
What is antibody complement activation?
An antibody bound to a pathogen will rapidly activate component proteins so that a pore is formed in the pathogen cell wall
What is meant by the “classes of antibody”?
The bottom of the antibody is the constant region that determines what sort of antibody it is.
How many classes of antibody are there?
5
What are the 5 classes of antibody?
IgG IgA IgM IgE IgD
What is the most abundant antibody?
IgG
What are the functions of IgG antibody?
- opsonisation
- neutralisation
- crosses the placenta to provide passive immunity
- targets viruses and bacteria
Describe the IgA antibody
- A dimer with a J chain in the secretory regions and a monomer in the blood
- present in secretions such as tears, saliva and breastmilk
What are the functions of IgA antibody?
- defence of mucous membranes especially the gut
- present in the breast milk to confer passive immunity to baby
- targets virus and bacteria
Describe the IgM antibody
- a pentamer
- the first Ig class produced after the initial exposure to the antigen
- expressed on naïve B cells
What are the functions of IgM antibody?
- very effective at activating complement
- targets extracellular bacteria
- acts as an antigen receptor (BCR)
Describe the IgE antibody
- a monomer that is present in blood at low concentrations
What are the functions of IgE antibody?
- provides immunity to multicellular parasites
- responsible for allergic reactions
Describe the IgD antibody
a monomer expressed in naïve B cells
What is the function of IgD antibody?
Together with IgM it acts as antigen receptor (BCR)
What is the main difference between T cells and B cells?
B cells recognise proteins, lipids and carbohydrates whereas T cells can recognise processed peptides
What two signals are required to release antigen?
- antigen recognition (ie. the B cells bind to the antigen)
2. receive T cell signals in the form of cytokines
Stimulation of B cells by antigens and T cells leads to the formation of
plasma cells
and a small pool of memory cells
Describe memory B cells
They express antibody as BCR but do not secrete antibody.
The persist for years in blood and lymphatic tissue
What are the two types of immune responses?
Primary and secondary
Describe the primary immune response
- takes around 7-14 days before sufficient antibody is produced to eliminate pathogen
- relatively low amount of antibody produced (mainly IgM)
Describe the secondary immune response
- relies on memory B cells
- fast (2-3 days) and sufficient antibody is produced to eliminate pathogen, mainly IgG
The antibodies important in providing passive immunity are
IgG and IgA
The antibody responsible for allergy is
IgE
The first antibody produced after initial antigen exposure is
IgM
The antibody that most effectively activates the complement system
IgM
The antibody that most effectively destroys multicellular parasites is
IgE
The BCR on naïve B cells is mainly composed of
IgD and IgM
The process of coating a microbe in antibody (or complement) is called
opsonisation
B cells recognise _______ via their _____, while T cells recognise ______ in the context of
native antigens
BCR
peptides
MHC
The primary immune response is characterised by the production of large amount of
IgM
The secondary immune response is characterised by the production of large amounts of
IgG
What is the purpose of defensins?
They help control bacterial and fungal colonisation of the exposed areas.
What is the purpose of lymph nodes?
they brings cells together so they can start talking to each other and get activated and then move back to the tissue where they are needed
What is a bacterial PAMPs of the flagella?
- flagellin
What is a bacterial PAMPs of the nucleic acid?
- unmethylated CpG DNA
What does SCID stand for?
Severe Combined Immunodeficiency
What cells are missing in a individual with SCID?
Functional T and B cells
True or false?
Every part of the body has immune cells? (explain)
False
Parts of the body without immune cells (such as the testes and the eye) are called immune privileged sites
What is central and peripheral tolerance?
When the T cells that recognise self antigens (ie. react against ourselves) are destroyed
Give an example of a disorder caused when the central and peripheral tolerance fails and so the immune cells attack our own body?
Rheumatoid arthritis
Briefly explain how rheumatoid arthritis occurs
The T cells and B cells recognise the tissue in our synovial joints as cells to attack
What is the difference between an autoimmune disease and an allergy?
An autoimmune disease is when the immune system recognises our own cells as cells to attack whereas an allergy is when the immune system attacks harmless foreign particles such as dust and pollen
What is type | hypersensitivity?
An allergic reaction
What is an example of an allergic reaction?
A peanut allergy
What is the most important cell involved in an allergic reaction?
Mast cells
What is the antibody most important in a hypersensitivity/allergic reaction?
IgE
What is the most important effector molecule involved in an allergic reaction?
Histamine
Describe how a peanut allergy can occur
- the first time peanuts are consumed, molecules from the peanut are picked up by the dendritic cells
- these are presented to T cells to find the same molecule recognition for the peanut allergen
- B cells pump out IgE
- IgE binds to mast cells
- the next time you have peanuts, the peanut molecules bind to the IgE on the mast cells
- the mast cells are stimulated which causes the release of histamine
What are some of the effects of histamine being released?
swelling, heat, edema
What happens when B cells pump out IgE?
they bind to mast cells
If you have a peanut allergy, the second time you have peanuts, what happens?
- the peanut molecules bind to the IgE on the mast cells
- the mast cells are stimulated which causes the release of histamine
What are lectins?
protein molecules that the innate immune system produces to recognise foreign invaders
What are the three physical and chemical barriers to bacterial invasion that are present on the skin?
- salt
- sebum
- dead cells and keratin
How does sebum provide a chemical barrier for the skin?
It is secreted out of the sebaceous glands (associated with the hair follicles). It has a low pH which inhibits the growth of microbes and it can trap microbes to make it easier for the phagocytes.
What are four physical and chemical barriers to bacterial invasion that are present in the gut?
- there is a constant flow of fluids to flush out pathogens
- stomach acid with low pH to inhibit the growth
- digestive enzymes
- bile
What does AMPs stand for?
Antimicrobial peptides
Give an example of an AMP and explain how it works
Defensins
are excreted from the skin, gut and airways and they have a charge so they can interact with the membrane of the outer cell wall of the bacteria causing it to break
Explain the role of a lysozyme and state where they are found
they are found in the skin and airways and the role is to break the bonds between the NAMs and NAGs of the peptidoglycan
What is diapedesis?
When the neutrophils change shape and move through the capillary walls
What are the two ways the adaptive immune response destroys viruses?
Using cellular and humoral means
What is meant by the adaptive immune response destroying viruses by cellular means?
By killing the infected cells
What is meant by the adaptive immune response destroying viruses by humoral means?
By attacking the unprocessed antigen
What are antibodies?
Proteins produced by B cells during an adaptive immune response, they activate complement, neutralise toxins or opsonise pathogens
Dendritic cells phagocytose the virus and present viral peptides on
MHC-| and MHC-||
Where do dendritic cells go from the skin?
They travel to the lymph nodes and present the antigen to the T cells
What is clonal selection and expansion for T cells?
Every T cell has a receptor for a specific antigen. When the DC travels to the lymph nodes, it searches for the T cell with the antigen receptor that matches the antigen it is presenting on its surface. These T cells are then expanded (ie. produced in greater numbers)
Explain how the adaptive immune response responds to intracellular pathogens such as viruses
The cytotoxic CD8 T cells travel around the body, searching for viral peptides presented on the surface of cells.
CD8 releases chemicals to kill these cells
What are the two chemicals released by CD8 and what are their roles?
- Perforin which punches a hole in the infected cell
2. Granzyme which travels into the cel via the hole and kills the cell and the virus inside
What is clonal selection and expansion for B cells?
B cells express unique antigen receptors on their surface. When unprocessed antigen is floating around the body, and it binds to these specific receptors, these B cells are then produced in greater numbers
What are the three ways antibodies stop the virus?
- neutralisation
- opsonisation
- complement activation
Describe the process of neutralisation
The antibodies cover the capsid of the virus so that it cannot attach to anything
What are the two components of vaccines?
- antigen
2. adjuvant
What is the role of antigen is a vaccine?
It is the specific molecule that the immune system has to recognise
It may have been heat killed, attenuated (passed through culture) or be recombinant viral proteins
