5: Cell recognition and the immune system Flashcards
A lymphocyte is a type of white blood cell, what are the two forms?
- cell mediated responses involving T lymphocytes
- humoral responses involving B lymphocytes
the specific tertiary structured proteins on cells allow the immune system to identify?
- pathogens
- non-self material
- toxins
- abnormal body cells
are lymphocytes produced in responses to an infection, or already exists
already exist. there are millions so there will be one lymphocyte with a complementary protein to a complementary protein on a pathogen
how lymphocytes recognise cells from your own body
- in fetus, lymphocytes constantly colliding with cells
- infection is rare in fetus as protected by placenta in mother
- some lymphocytes will have receptors that fit those of own body cells - this are killed
- the remaining owning respond to foreign material
- any that show immune response undergo programmed cell death before they can differentiate into mature lymphocytes
two types of white blood cells:
- lymphoctyes (immune response)
- phagocytes (phagocytosis)
Process of phagocytosis (non specific defence mechanism like physical barriers)
- chemical products of pathogen act as an attractent to the phagocyte
- so move towards
- phagocytes have receptors that recognise and attach to these chemicals
- engulfs pathogen to form a vesicle called a phagosome
- lysosomes move towards vesicle and fuse with it
- enzymes lysozymes destroy ingested bacteria by breakdown of cell walls by hydrolysis
- the soluble products from breakdown are absorbed into phagocyte cytoplasm
Antigen
part of an organism that is recognised as non self by the immune system and so stimulates an immune response
Specific defence mechanism
- lymphocytes
slower but provide long term immunity, they are produced by stem cells in bone marrow
B lymphocytes
- mature in bone marrow
- humoral immunity, which involves antibodies present in body fluids
T lymphocytes
- mature in thymus gland
- associated with cell mediated immunity (involving body cells)
Cell mediated immunity
- respond to own cells affected by non-self material (virus)
- respond to non-self cells, which have different antigens than own.
T lymphocytes can distinguish these invade cells by - phagocytes present the pathogens antigens
- body cells invaded by virus present virus antigens
- transplanted cells have diff antigens presented than our own
- cancer cells are different than normal cells and present antigens
(cells displaying foreign antigens = antigen-presenting cells)
stages in response of T lymphocytes to infection from pathogen
1 - pathogens invades body cells or taken in by phagocyte
2 - phagocytes presents pathogens antigens on cell membrane
3 - receptors on specific t cell fit exactly to these antigens
4 - t cell divides rapidly by mitosis
5 - clone t cells turn into memory cells for rapid response, stimulates phagocytosis, stimulates b cells to divide and secrete antibody, activate cytotoxic t cells
how do cytotoxic t cells kill infected cells
produces protein that makes holes in cell membrane of infected cells
T cells =
cell mediated response
B cells =
humoral immunity
Humoral immunity (b cells)
- produces antibodies that are soluble in blood
- each specific b cell produces a specific antibody that responds to one specific antigen
- when an antigen enters the blood, an antibody on b cell will be complementary to it
- the antigen then enters the b cell by endocytosis and gets presented on its surface
- t cells bind to this presented antigen and stimulate the b cell to divide by mitosis to form a clone of identical b cells - clonal selection
In each clone of the b cell, the cells produced turn into either
- plasma cells (secrete antibodies into the blood plasma. primary immune response)
- memory cells (secondary immune response, live longer than plasma cells, dont produce antibodies but when come across antigen they divide into plasma cells)
Antibodies
proteins with specific binding sites synthesised by b cells. b cells produce the specific antibody needed, which reacts with antigen by binding (antigen-antibody complex)
- each antibody has two identical binding sites
- antibodies are made of four polypeptide chains
- the chains of one pair are long - heavy chains
- the chains of the other pair are short - light chains
- binding site is the variable region, the rest of the antibody is the constant region
do antibodys directly destroy the anitgen or prepare the antigen for destruction (and whats an example)
prepares the antigen for destruction
- when an antigen is a bacterial cell, the anitbody will
1. cause agglutination of the bacterial cells. they r clumped together so easier for phagocyte to locate
2. then serve as markers to stimulate phagocytes to engulf
monoclonal antibodies
single type of antibody can be isolated and cloned (from b cells). useful in science and medicine.
what are monoclonal antibodies successful in treating
(direct therapy)
- cancer cells.
- monoclonal antibodies produced, specific to antigens on cancer cells
- antibodies given to patient, and attach themselves to receptors on cancer cells
- attach to surface of cancer cells and block the chemicals signals that stimulate there uncontrollable growth
(herceptin for breast cancer cells)
indirect therapy of monoclonal antibodies
involves attaching a cytotoxic drug to the monoclonal antibody, can be released in smaller doses so cheaper and less side effects
medical diagnosis using monoclonal antibodies
particular antigens are targeted by the antibody to measure the levels of antigen in the body (can detect cancer cells, hiv, pregnant)
Pregnancy testing
placenta produces the hormone hCG, found in mothers urine. if hcg present it binds to the monoclonal antibodies present. the hcg-antibody-colour complex moves along strip until trapped by a different type of antibody producing a coloured line
Ethical use of monoclonal antibodies
- using mice to produce antibodies and tumour cells which is deliberately inducing cancer in them
- some people die, important to know risks and benefits (informed consent)
- drug trials, organ failure in volunteers
Two forms of immunity
- Passive immunity (introduction of antibodies from another human or animal, no direct contact with antigen needed)
- Active immunity (production of antibodies from the immune system, direct contact with the pathogen is necessary).
Active immunty, two types
- natural active immunity (infected with disease under normal circumstance)
- artificial active immunity (vacination - immunisation, inducing immune response with no symptoms)
Success of vaccine depends on
- economically available in sufficient quantities
- few side effects
- means of producing, storing and transporting vaccine must be available
- administering the vaccine appropriately (training staff)
- possible to vaccinate large majority of population for herd immunity
The structure of virus ‘human immunodeficiency disease’
- cause the disease AIDS
- lipid envelope, embedded are attachment proteins
- inside is the protein layer called the capsid which encloses two single strands of RNA and some enzymes.
- one of these enzymes is reverse transcriptase catalysed the production of DNA from RNA
- hiv belongs to virus group - retroviruses
Replication of hiv
as its virus it cant replicate itself.
- hiv virus protein binds to protein CD4 (most commonly found on t helper cells)
- protein capsid fuses with cell surface membrane and rna and enzymes of hiv enter the helper t cell
- the hiv reverse transcriptase coverts viruses rna to dna
- this new dna moves into t cells nucleus and inserted into dna
- this creates mRNA
the ELISA test
- detects presence and quantity of the HIV antigen
1. sample in well which contains antigen
2. antigen molecules stick to bottom
3. wash the well several times to remove any that didnt stick
4. add antibody which is specific for antigen, wait for them to stick
5. wash well to remove excess antibodys
6. add second antibody with eznyme that binds with first antibody
7. wash to remove any ubound second antibodys
8. add colourless substrate that colours when with enzyme
relative to intensity of colour
Why are antibiotices ineffective for hiv and viruses
- antibiotics work by preventing bacteria from making cell walls
- viruses dont have a cell wall and are made inside host cell
instead treated with antiretroviral
