immune system Flashcards
what is a vaccination?
a medical procedure that involves administering a weakened or dead form of a pathogen in a person, to trigger the production of antibodies
how do vaccines work?
dead/weakened viral preparations have antigens to stimulate the immune system to recognize and eliminate the particular pathogen, so if it reenters, the body can detect and eliminate it. they cause memory cells to be created
when does herd immunity occur
when large proportion of the population has been vaccinated which makes it difficult for pathogens to spread. those who aren’t immunized are protected as its unlikely to contract the disease as the levels of it are low
how does active immunity work?
the body makes its own antibodies in response to pathogen exposure
- vaccination provides active immunity (booster vaccinations are needed)
features of active immunity?
- long term
- takes a long time to develop immunity
- body produces antibodies in response to pathogen exposure
- produces memory cells
how does passive immunity work?
develops due to antibodies which come form another animal
features of passive immunity
- short term
- develops immunity fast
- body develops immunity due to antibodies which came from another animal
- doesn’t produce memory cells so antibodies get used up
Why it is easier to develop vaccines for some diseases and not others
some viruses are able to undergo rapid modifications. these modifications allow viruses to easily evade the immune system and most of the vaccines fail to work against these viruses
What is a pathogen
A microorganism that causes a disease
1st line fo defence
Physical:
- skin
- cilia
- mucus
- nasal hair
- friendly bacteria
1st line of defence
Chemical:
- mucus
- tears, lysosomes
- stomach acid, HCL
- platelets
Process of phagocytosis
- Phagocyte is attracted to the pathogen by chemotaxis
- Pathogen attaches to phagocyte by antibody and surface receptors
- Pathogen engulfed by an infolding of the phagocyte membrane
- Lysosomes release sets lysines into phagosomes
- Harmless end products of digestion are absorbed
- Phagocyte displays the antigens form the pathogen on its cell surface membrane and becomes an antigen presenting cell (APC)
What is a macrophage
Phagocyte ell that releases lytic enzymes to break down pathogenic cell
What is a cytotoxic T cell
Cells that destroys pathogenic cells by releasing chemical into the invaded cells
What is a Helper T cell
Cell that stimulates and recruits more cells to assist in the immune response
What are b lymphocytes
Are responsible for humorous immunity (the humours = body fluids). They produce antibodies
What are t lymphocytes
Are responsible for cell mediated (requires cells) immunity
Cell maturation of b lymphocytes and t lymphocytes
Both cells begin life as stem cells in the bone marrow
- T cells mature in the thymus
- B cells mature in the bone marrow
What are antigens
part of an organism/ substance thats recognized as foreign by the immune system, which stimulates an immune response.
They are often proteins or glycoproteins on the cell surface membrane
Features of cell mediated immunity
- cell mediated response can only be initiated by APc’s
- cell mediated responses are specific to the antigens presented
Examples of APC’s:
- phagocytes that have engulfed, invading microorganisms
- cells which ave been infected by a virus
- cancer cells
- cells transplanted from anther organism
Any of these can trigger an immune response
Process of cell-mediated immunity
- Phagocyte ingest pathogens by phagocytosis
- Pathogens is digests and the cell becomes an APC
- T helper cells attracted to phagocyte by chemicals
- T helper cell binds to antigen on surface of phagocyte
- T helper cell undergoes clonal expansion
- Clones activate cytotoxic T cells
- Cytotoxic T cells bind to antigens and secrete performing
- Perforin makes holes in the pathogen membrane and kills the cell
- Some T cells remain as memory cells
B lymphocytes activation process
- T helper cells active specific B cells
- Once activated the B cells undergo clonal expansion and differentiate to form either plasma cells or memory cells
What a plasma cells
produce antibodies which are complementary to the antigens on the pathogen
What are memory cells
Memory cells remain circulating the blood for periods of time.
The next time the same pathogen invades they turn into plasma cells and produce more antibodies, more quickly (secondary response is faster and stronger)
Process of monoclonal antibody production
- Mouse is exposed to antigens which antibody is required
- B cells in the mouse produce a mixture of antibodies
- This is extracted from the spleen of the mouse
- B cells are mixed when cells that divide readily outside the body e.g. tumour cells
- Detergents is added to break the plasma membranes in the cells so they fuse and form hybridoma cells
- Hybridoma cells are separated each one is cultured to form a clone
- Any clone producing the required antibody is grown on a large scale & the antibodies are extracted
What can Monoclonal antibodies used:
- to target cells
- for molecule detection, e.g. pregnancy testing used to detect the hormones hCG
How can moloclonal antibodies be used to target cells?
- cancer cells contain specific antigens called tumour markers
- anti-cancer drugs can be attached to the complementary antibodies
This allows for more specific targeting of cancer cells and fewer side effects from the drugs
What does ELISA stand for and what is it
Enzyme linked immunosorbent assay
ELISA is a technique used to detect (assay) specific molecules (e.g. proteins & carbs) in samples
Features of the ELISA method
Immunological technique: uses antibodies
Quantitative
Very sensitive
Used in medicine and scientific research
Basic steps of ELISA
- Antigens are bound onto plastic surface (sorbent)
- Antigen of interest is recognised by a specific antibody (immuno)
- This antibody is recognised by a second antibody (immuno) which has an enzyme attached (enzyme-linked)
- Substrate is hydrolysed by the enzyme to produce a product usually coloured
Amount of coloured product= quantitative measure of antigen present
What is a direct assay
Enzyme attached a primary antibody
What is an indirect assay
Enzyme attached to the secondary antibody
Why do you to do the first wash in ELISA
want the antigens to be fixed in place
Why do you want to do the second wash in ELISA
so there are no floating primary antibody that the secondary one can bind to
Why do you have to do the last wash in ELISA
to remove any floating secondary antibody so the substrate won’t bind, which could give a false positive
Uses of ELISA:
- disease detection in people, animals and plants (e.g. HIV in humans)
- detection of allergens in food e.g. peanuts
- detection of illegal drugs in humans
- detection of hormones e.g. pregnancy testing kit
what is HIV?
human immuno-deficiency virus
its a retrovirus
what does hiv infect?
t helper cells (host cells)
what does HIV contain
RNA, not DNA
how is viral DNA made
by the host cell from the RNA using the viral enzyme reverse transcriptase
how is viral DNA incorporated into host DNA?
via viral enzyme integrase in the nucleus
how does a membrane enveloped virus benefit HIV
allows the cell to fuse with other cells more easily, as it gives it seamless entry
process of HIV entering the body?
1.virus binds to receptor of plasma membrane on helper T cells
2. virus envelope fuses with plasma membrane allowing the viral RNA and enzymes to enter the cell
3. virus reverse transcriptase copies viral RNA into viral DNA
4. Integrase inserts viral DNA into host DNA
5. translation of virus envelope proteins
6. transport of virus envelope protein’s
7. virus envelope proteins are incorporated into the cell membrane
8. virus particle budding becomes wrapped in plasma membrane forming the virus, and is released
how are t lymphocytes killed by HIV
- killed when the HIV virus exits the t cell via budding
- infected helper cells are destroyed by cytotoxic t cells
what happens due to loss of t helper cells
loss of activation of both t and b cells so the effectiveness of the specific immune response is reduced
what is AIDS
the collection of diseases that result from the destruction of t helper cells
Structure of an antibody
- 4 polypeptide chains he’ll together by disulphide bridges
- each antigen can bind to two antibody binding sites at a time
Different regions on an antibody
- generic constant region - binds to lymphocytes
- variable region - its complementary to a specific antigen and forms the antigen binding site
- hinge region - allows the antibody to flexi in order to bind to more than one antigen at a time
What is agglutination?
- antibodies cause pathogens to stick together
- makes it easier for phagocytes to engulf them
What is neutralisation with an antibody
- pathogens cause illness by producing toxins
- some antibodies work by neutralising these toxins by binding to them
what are antibodies affect on viruses
antibodies can bind to viruses and stop them attaching to their host cell
What’s a polyclonal antibody
A diverse antigen binding site. They can only recognise a particular antigen but can recognise different variations of it
