Immunology Flashcards
(54 cards)
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)
- Antigen presenting cell (phagocyte) presents antigen on its cell surface
- t cell with complementary protein receptor will bind to antigen
- stimulates t cells to divide by mitosis and form clones of identical t cells
What do the cloned 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
