2C - The Immune System Flashcards
What are antigens
Molecules (usually proteins) that generate immune responses when detected by the body.
- usually found on the surface of cells and used by immune system to identify..
Pathogens (organisms that cause disease)
Abnormal body cells (cancerous or pathogen infected cells - abnormal antigens on surface)
Toxins
Cells from other individuals of same species (transplants)
What are the first of four main stages in immune response
- Phagocytes engulf pathogens
Phagocytes (eg. A macrophage) is a type of white blood cell that carries out phagocytosis
—> engulfment of pathogens
They’re found in blood and tissues
And are first cells to respond to immune system triggers in body
— phagocytes recognise foreign antigens on a pathogen
— cytoplasm of phagocyte moves round pathogen, engulfing it
— Pathogen’s contained in a phagocytes vacuole (a bubble) in phagocytes cytoplasm
— lysosome fuses with phagocytes vacuole, lysozymes from it break pathogen down
— phagocyte presents pathogen’s antigens , to activate other immune system cells
diagram no.2
What’s the second of four main stages in immune response
- Phagocytes activate T cells
—> T cells (T-Lymphocytes) is another type of white blood cell
— has receptor proteins on its surface that bind to complimentary antigens
Presented to it by phagocytes
This activates the T Cell; different t cell types respond in different ways.
Like t helper cells release chemical signals that
activate and stimulate phagocytes and cytotoxic T cells
—> cytotoxic t cells kill foreign and abnormal cells
T^h cells also activate B cells - they secrete antibodies
What’s the third of four main stages in immune response
T cells activate B cells (divide into plasma cells)
B cells/lymphocytes are a type of white blood cell,
covered with antibodies (proteins that bind antigens to form antigen-antibody complex)
- each B cell has a diff shaped antibody on its membrane
- so diff ones bind to diff shaped antigens
- When the antibody on the surface of the B cell
meets a complimentary shaped antigen, it binds - This with the substances released from t helper cells
Activates B cell (clonal selection) - Activated b cell divides into plasma cells
What’s the fourth of four main stages in immune response
Plasma cells make more antibodies to a specific antigen
- plasma cells are clones to b cell
- they secrete lots of antibodies specific to antigen (monoclonal antibodies)
- they bind to the antigens on the surface of pathogen to form antigen antibody complexes
An antibody has two binding sites
So can bind to two pathogens , meaning pathogens clump together (aggultination)
Phagocytes then bind to the antibodies
And phagocytosis happens to many pathogens at once
This process threads to destruction of pathogens carrying this antigen in the body
Antibody structure?
Antibodies are proteins - made up of amino acid chains
The specificity of an antibody depends on its variable regions (form antigen bind sites)
Each antibody has variable region with a unique tertiary structure (due to diff amino acid seq)
That’s complimentary to one specific antigen all antibodies still have the same constant region
diagram no.1
What can the immune response be split into
- cellular response
T cells and other immune system cells that they interact with
Like phagocytes form cellular response - humoral
B cells, clonal selection and production of monoclonal antibodies form humoral
Both types are needed to remove a pathogen from the body
And responses interact with each other
(Eg. T cells help activate B cells and antibodies coat pathogens making it easier for phagocytes to engulf)
What are the four steps of immune response diagram
Diagram no 3
What’s the primary immune response
- When antigen enters body for first time it activates the 8mmune system (primary response)
- it’s slow because there aren’t many b cells that can make antibody to bind to it - Eventually body will produce enough of the right antibody
Meanwhile infected person will show the disease’s symptoms - After being exposed to the antigen, t and b cells
Will produce memory cells (stay in body for long time)
— memory t cells remember specific antigen and will recognise second time round
— memory b cells record specific antibodies needed to bind to antigen - Person is now immune (immune system has ability to respond fast to a second infection by the same antigen/pathogen)
What’s the secondary immune response
If the same pathogens enters the body again ,
Immune response will be quicker and stronger (this is secondary)
— clonal selection happens faster.
— memory b cells (b-lymphocytes) are activated, dividing into
plasma cells that produce right antibody to the antigen
— memory T cells (t-lymphocytes) are activated, dividing into
correct T cell type to kill cell carrying antigen
Secondary response often rids of pathogen before symptoms show (you’re immune to pathogen)
diagram no.4
Is the graph of conc of right antibody in blood on both exposures
What exactly are memory cells ?
Memory cells are types of b and t lymphocytes
They just remain in blood longer than most t and b cells
When antigen enters body for a second time they can immediately divide
Into more specific b and T cells that can kill pathogen/release antibodies against
How do vaccines work to protect individuals/populations against disease
Vaccinations help avoid you suffering from disease
As b cells have to divide to build up numbers and deal with pathogen,
which takes a while meaning symptoms show
-
- vaccines have the antigens that cause your body to produce memory cells
- against that specific pathogen, without pathogen causing disease
Means immunity without symptoms
The antigens in the vaccine are free
OR attached to a dead/attenuated (weakened) pathogen
What is herd immunity
It’s where vaccines protect individuals that have had the vaccine
As well as reducing diseases’ occurrence
-> as those who aren’t vaccinated are less likely to catch disease
-> bc fewer ppl to catch it from
How are vaccines intaken
May be injected or intaken orally
Disadvantages of intaking orally
Are that antigens could be broken down by enzymes in gut
Or molecules may be too large to be absorbed by blood
- sometimes booster vaccines are taken later (years after)
- to ensure memory cells are still produced
What’s antigenic variation
It helps some pathogens evade the immune system
- antigens on pathogen surface activate primary response
- you don’t get ill during secondary response
- however some pathogens change surface antigens (antigenic variation)
- diff antigens are due to changes in genes of a pathogen
This means that when infected for a second time, memory cells produced
From first won’t recognise different antigens
so immune system starts from scratch (another primary response with new antigens)
—> Primary response takes time to rid of infection
So you get ill again
Antigenic variation makes it difficult to make vaccines against some pathogens
Some are HIV and influenza virus
How does antigenic variation affect production of vaccines to prevent catching influenza
Influenza (flu) vaccine changes every year
As antigens change regularly (new strains of virus made)
Memory cells from vaccination with one strain of flu
Don’t recognise other strains (diff antigens)
—> strains are immunologically distinct
Different vaccine made each year for flu
Due to diff strains each year circulating population
New vaccines are developed and one is chosen every year
that’s most effective against recently circulating influenza
Governments and health authorities then implement
a programme of vaccination using suitable vaccine
Difference between active and passive immunity
Active
- type of immunity you get when immune system makes its own antibodies
- after being stimulated by an antigen
The two types of active immunity are
Natural: immune after catching disease
Artificial: immune after vaccine with harmless dose of antigen
.
Passive
- immunity gotten from being given antibodies made by different organism
- no antibodies produced of its own
The two types are
Natural: baby becomes immune due to antibodies from mother (placenta and breast milk)
Artificial: immune after injected with someone else’s antibodies - eg blood donations
What are the differences between passive and active immunity
Active
- requires pathogen exposure
- takes a while for protection to develop
- memory cells made
- long term protection (antibody produced by memory cell activation
In response to complimentary antigen present in body)
.
Passive
- no exposure to antigen needed
- protection is immediate
- no memory cells
- short term protection as antibodies given are broken down
What are monoclonal antibodies AND how are they made
These are antibodies produced from a single group
of genetically identical b cells/plasma cells
- antibodies are very specific because their binding sites
have unique tertiary struc (one antigen can fit with complimentary shape)
How are monoclonal antibodies made to target drugs to cancer cells
Can be made to bind to anything you want (eg. Cell antigen)
Will only bind to this molecule only
1. Diff cells in body have diff antigens (eg. Cancer cells have
antigens called tumour markers - not found on normal body cells)
2. Monoclonal antibodies can be made to bind to tumour markers
You can also attach anticancer drugs to antibodies
- When antibodies come into contact with
cancer cells they will bind to tumour markers - Meaning drug will only accumulate (come together)
on body where cancer cells are - Side effects of antibody based drug are lower than other drugs
As they accumulate near specific cells
How are monoclonal antibodies used to target substance for pregnancy tests (medical diagnosis)
Pregnancy tests detect human chorionic gonadotropin (HCG)
in the urine of pregnant women (a hormone)
1. Application area has antibodies for HCG
bound to a blue coloured bead
2. When urine applied to application area any HCG
Will bind to the antibody on beads, forming an antigen antibody complex
- Urine moves up stick to test strip, carrying any beads with it
- Test strip has also antibodies for HCG stuck in place (immobilised)
- If HCG is present, test strip turns blue as immobilised antibody bind to HCG
Concentrating the HCG Antibody complex with blue beads attached
If no HCG is present, the beads will pass through test area without binding (won’t go blue)
What’s the elisa test
(A medical diagnostic test that uses antibodies)
The enzyme-linked immunoabsorbent assay (ELISA)
Allows you to see if a patient has any antibodies to a certain antigen (or vice versa)
—> can be used as a test for pathogenic infections, for allergies
And for anything you can make antibodies for
In an ELISA test, an antibody is used wch has an enzyme attached to it
This enzyme can react with substrate to produce a coloured product
—> causes solution in the reaction vessel to change colour
— if there’s a colour change, an antigen/antibody of interest is there
— the quantity of antigen/body can be worked out from intensity of colour change
What’s an example of an ELISA test
There are several types of ELISA
- direct elisa uses single antibody that’s complimentary to antigen tested for
- indirect elisa uses two diff antibodies
.
Indirect elisa can be used to see if a patient has antibodies to HIV
- HIV antigen is bound to bottom of well in well plate
(A plastic tray with loads of little circular pits/wells in it) - A sample of patient’s blood plasma (may contain several antibodies)
Is added to well
If any HIV specific antibodies, they will bind to HIV antigen
Stuck to bottom of the well (wch is then washed out to remove unbound antibodies) - A secondary antibody with specific enzyme attached is added to well
Secondary antibody can bind to HIV antibody (primary antibody) - Well is washed out again to remove any unbound secondary antibody
(If no primary antibody in sample, secondary antibody will wash away) - A solution is added to well (containing substrate able to react with enzyme attached to secondary antibody and produce a coloured product)
- if solution changes colour, indicates patient has HIV antibodies
- and hence IS INFECTED with HIV
Why are washing steps important in elisa test
To ensure unbound antibodies aren’t left in well (may affect end result by making test appear positive at end even if no HIV antibodies present)
If the elisa test was negative there’d be no colour change as
There’d be no HIV specific antibodies for secondary antibodies to bind to
