Module 4 : Section 1 - The Immune System Flashcards
What triggers an immune response
Foreign antigens
What are antigens
Molecules (usually proteins or polysaccharide) found in the surface of cells
What happens when a pathogen (e.g. bacterium) invades the body
The antigens in its cell surface are identified as foreign so this activated the cells in the immune system
What two stages are involved in the immune response
- specific
- non-specific
What is the specific and non specific responses
- non specific happens in the same way for all microorganisms no matter what antigens they have
- specific response is antigen-specific which involves white blood cells and T and B lymphocytes
What are the four main stages in the immune response
- phagocytes engulf pathogens
- phagocytes activate T lymphocytes
- T lymphocytes activate B lymphocytes which divide to plasma cells
- plasma cells make more antibodies to a specific antigen
What is a phagocyte
- A white blood cell that carries out phagocytosis
- they are found in blood and tissues, they carry out a non specific immune response
How do phagocytes work
- it recognises the antigens on a pathogen
- phagocytes cytoplasm moves round the pathogen (engulfing it) presence of opsonins make it easier when engulfing
- the pathogen now contained in a phagosome in the cytoplasm of a phagocyte
- a lysosome fuses with the phagosome, the enzymes in the Lysosome break down the pathogen
- phagocyte then present the pathogens antigens on its surface to activate other immune system cells. It acts as an antigen presenting cell
What are neutrophils
- first type of white blood cell to respond to a pathogen
- they move towards a wound in response to signals from cytokines which get released by cells at the site of the wound
What are opsonins
Molecules in the blood that attach to foreign antigens to aid phagocytosis
what does cell communication consist of (phagocytes activating t lymphocytes)
- presentation
- clonal selection
- clonal expansion
- differentiation
what is the presentation stage of cell communication
the antigens are presented by an antigen presenting cell
what is clonal selection
- when the receptor of a t lymphocytes meets a complementary antigen it binds to it
- each lymphocyte will bind to a different antigen
- this activates the t lymphocyte
what is clonal expansion
when the chosen t lymphocyte divides to produce clones of itself
what is differentiation
the process in which the t lymphocytes become either t helper, killer or regulatory cells or memory cells
what do t helper cells do
these release substances to activate B lymphocytes and T killer cells
what do t killer cells do
these attach to and kill cells that are infected with the virus
what do t regulatory cells do
these suppress the immune response from other WBC’s. this helps stop immune system cells from mistakenly attacking the host’s body cell
what are b lymphocytes
- type of white blood cell
- covered with proteins called antibodies
- each b lymphocyte has a different shaped antibody on its surface, meaning each of them will bind to a different antigen
what do antibodies do
bind to antigens to form an antibody-antigen complex
when a b lymphocyte is selected what happens
it divides by mitosis into plasma cells and memory cells
What are plasma cells
- Clones of the b lymphocyte (identical to the selected b lymphocyte)
- they secrete loads of the antibody which is specific to the antigen into the blood
What is the variable region of an antibody
- forms the antigen binding site and the shape of this is complementary to a particular antigen
- found in the tips of the antibody
- differs between antibodies
What is the hinge region of an antibody
Allows flexibility when the antibody binds to the antigen
What is the constant region of the antibody
- they allow binding to receptors on immune system cells
- this is the same (same sequence of amino acids) in all antibodies
What is the disulphide bridges in the antibody
A bond which hold the polypeptide chains of the protein (antibody) together
What methods do anitbodies use to help clear infections
- agglutination
- neutralising toxins
- preventing the pathogen binding to human cells
What is agglutination
- each antibody has two binding sites, so an antibody can bind to two pathogens at the same time
- they then become clumped
- phagocytes then bind to the antibodies and phagocytose all at once
How does the method of neutralising toxins work when antibodies clear infections
- toxins have different shapes than antigens
- antibodies called anti-toxins can bind to the toxins produced by pathogens
- this prevents the toxins from affecting human cells
- these are also phagocytosed
What is the primary response
When a pathogen enters the body for the first time, the antigens on its surface activate the immune system
Why is the primary response slow
- Because there aren’t many B lymphocytes that can make the antibody needed to bind to it
- overtime the body will produce enough of the right antibody to overcome the infection while the infected person shows symptoms
What happens after being exposed to an antigen
T and B lymphocytes produce memory cells
Memory T lymphocytes remember….
The specific antigen and will recognise it the second time round
Memory B lymphocytes remember
The specific antibodies needed to bind to the antigen
What happens if the same pathogen enters the body again
The immune response will produce a quicker, stronger immune response. Known as the secondary response
Why is the secondary response faster
- Clonal selection happens faster
- The memory B lymphocytes are activated and divide into plasma cells that produce the right antibody to the antigen
- the memory t lymphocytes are activated and divide into the correct type of t lymphocyte to kill the cell carrying the antigen
- this happens before you show any symptoms
