Immunology Flashcards
What is a pathogen?
a disease causing organism
Describe a virus.
acellular and non living
no nucleus, organelles, cytoplasm or cell membrane
What does a virus particle contain?
- genetic material (RNA/DNA)
- capsid
- envelope
- attachment protein
Where did viruses replicate?
in host cells
How are viruses replicated?
- attach to host cell with complementary receptors
- inject nucleic acid(RNA/DNA) into to host cell
- genetic material codes for more virus particles
- these are produced using organelles of the host cell
- produce copies of nucleic acids and proteins to form complete viruses
- viruses are released by lysis of the cell
What are non specific defence mechanisms?
- the response is the immediate and the same for all pathogens
• physical barrier (skin)
• phagocytosis
Describe phagocytosis:
- phagocyte engulfs pathogen
- lysosome containing enzyme lysozyme fuses with phagosome and hydrolyse the pathogen
phagocyte can present antigen onto their cell surface membrane
What are specific defence mechanisms?
Response is slower and specific to each pathogen
- t cells (cellular response)
- b cells (humoral)
What is an antigen?
A protein/glycoprotein that may appear foreign to individual organisms exposed to them
• stimulate production if antibodies by b cells
Where may antigens be present?
- surface if pathogen
- cell surface membrane of other organisms of the same species
- abnormal body cells (cancer)
- as a toxin
Describe the Humoral response ( B cells)
- b cells secrete antibodies into their surface
- antigen complementary to antibody on b cell will bind
- this stimulates b cell to divide by mitosis (clonal selection)
-helpers t cells help them to divide - mitosis results in many plasma cells
- plasma cells produce the same specific antibody and secrete it into blood plasma
- some b cells divide into memory b cells
How do antibodies destroy antigens?
antibodies secreted by plasma cells bind to complementary antigen and form antigen-antibody complex
- stimulates processes leading to antigen being destroyed
What is the primary response?
First response to new pathogen
- relatively slow and takes 72hrs to produce a significant concentration of antibody
- symptoms may occur during this time
How do memory B cells lead to the secondary response?
if the same antigen is encountered memory b cells will divide and develop into plasma cells
- these plasma cells secrete antibodies more
quickly and a higher concentration if them - provides immunity as pathogens are destroyed before symptoms develop
What is antigenic variation?
Some microorganisms have a high mutation rate
so even though you may be immune to one strain of the virus this wont provide immunity for any new forms
Where can antibodies be found?
breast milk
blood plasma
tissue fluid
Describe the structure if an antibody.
four polypeptide chains
2 heavy chains 2 light chains joined by disulphide bonds
what is the constant region of the antibody?
the sequence of amino acids is the same for every antibody
what is the variable region if the antibody?
sequence of amino acids vary between different molecules
Which processes destroy pathogens?
agglutination of antigens
stimulation of phagocytosis
What is agglutination?
clumping together cells containing the antigen specific to the antibodies
- antibody uses its two binding sites to attatch to the same antigen present on two different cells
- joins them together forming a massive clump of cells which is easily destroyed
How is phagocytosis stimulated?
an antibody attaches to the antigen on pathogen and identifies it for destruction by phagocytosis
- phagocytes have receptors that recognise the antibody and enable them to bind to engulf the pathogen
Describe the Cellular response ( t cells)
- phagocyte presents antigen on its surface
- t cell with complementary protein receptor will bing to antigen
- stimulates t cells to divide by mitosis and form clones of identical t cells
What do the clones t cells do?
- activate cytotoxic t cells which attach to antigen and secrete chemicals to destroy it
- develop into more helper t cells which stimulate b cells to divide
- develop into memory t cells which remain in blood
What is passive immunity?
Where individual receives pre formed antibodies from an outside source
- person not exposed to the antigens and don’t form antibodies of memory cells
- short term immunity
What is natural passive immunity?
antibodies are obtained across the placenta and through breast milk
this provides short-term immunity
What is artificial passive immunity?
pre-formed antibodies are injected following exposure to infectious toxins/pathogen
short term protection
What is active immunity?
individual is exposed to antigens and produces antibodies and memory cells
long term immunity
What is natural active immunity?
results from the individual being infected and exposed to specific antigen
long term immunity
What is artificial active immunity?
results from an individual being vaccinated and immune system produces its own antibodies
What is in a vaccine?
vaccine contains antigens from a dead/weakened pathogen
How does a vaccine work?
Injection stimulates primary immune response which produces plasma and memory b/t cells
What is Herd immunity?
The higher the percentage of the population vaccinated against a pathogen the less risk of transmission
There is a low probability of an infected person encountering someone without immunity
What is in HIV?
- enzyme reverse transcriptase
- RNA
- attachment protein
- capsid
- viral envelope
How can HIV be transmitted?
- sex
- blood transfusions
- sharing needles
- mother to baby (placenta)
What is the function of the glycoprotein spikes?
They attach to complementary protein receptors on T cells
How is RNA and reverse transcriptase released into the T cell
The lipid envelope fuses with the cell membrane of the host cell this releases RNA and RT
What is the function of reverse transcriptase?
Uses RNA as a template to form viral DNA
- this viral DNA enters nucleus and attaches to host DNA
(can remain inactive for a long time)
What is the function of the viral DNA?
controls the synthesis of viral RNA
What is the function of viral RNA?
controls synthesis of viral proteins and more viral RNA
How does HIV lead to AIDS?
They destroy T cells meaning the immune system no longer works and can’t fight off infections
What is the first phases of the development of AIDS?
body produces HIV antibodies (may be flue-like illness)
What is the second phases of the development of AIDS?
HIV positive phase
- the period between infection and the beginning of clinical signs
What is the third phases of the development of AIDS?
AIDS-related complex
- results in a variety of microbial infections as number of T cells decrease
What is the fourth phases of the development of AIDS?
Infections of body organs, possible cancers, weight loss, may die from pneumonia
How do antibiotics work?
the affect cellular structures of bacteria such as, cell wall and ribosomes
Why don’t antibiotics work for viruses?
Viruses don’t possess cellular structures
What are monoclonal antibodies?
identical antibodies with the same antigen binding sites
How do monoclonal antibodies target medication to specific cells?
a therapeutic drug is attached to an antibody
toxic cells have different antigens to healthy cells
monoclonal antibodies with a toxic drug attached can kill these cells without affecting healthy ones
How are monoclonal antibodies used for medical diagnosis?
they can detect the presence of specific antigens of antibodies
What is a direct ELISA test?
measures the concentration ANTIGENS and can determine if a pathogen is oresent
What is an Indirect ELISA test?
measure’s concentration of ANTIBODIES and determine if someone has antibodies against a specific pathogen
Describe a direct ELISA test
- monoclonal antibody added to well
- sample added and if specific antigen is present it will bind
- second monoclonal antibody is added with enzyme attatched to it
- well should be washed to remove any unbound second antibody
- substrate for enzyme is added
- if the enzyme is still present the colourless substrate turns into coloured product
Describe an indirect ELISA test?
its the same as a direct ELISA but in an antigen is added to the well
