The immune system Flashcards
What are T helper/killer/regulatory cells?
T helper cells - release substances to activate B lymphocytes + T killer cells
T killer cells- these attach to + kill cells that are infected with a virus
T regulatory cells - these suppress the immune response from other WBC. Helps stop immune system cells from mistakenly attaching the hosts body cells
How do foreign antigens trigger an immune response?
Antigens are molecules on the surface of cells
When a pathogen invades the body, the antigens on its cell surface are identified as foreign, which activates the immune system
The immune response involves specific and non-specific response happens in the same way for all microorganisms - whatever foreign antigens they have. The specific response is antigen-specific. Its aimed at specific pathogens (involves WBC called T and B lymphocytes)
- Phagacytes engulf pathogens
A phagocyte recognises the antigens on a pathogen.
The cytoplasm of the phagocyte moves round the pathogen, engulfing it. Made easier by opsonins ( molecules in blood that attach ot foreign antigens to aid phagocytes)
THe pathogen is now contained in a phagosome
A lysosome fuses with the phagosome.. The enzymes break down the pathogen
The phagocyte then presents the pathogens antigens. It sticks the antigens on its surface to activate other immune system cells. When a phagocyte does this is is acting as an anti-presenting cell (APC)
- Phagocytes activate T lymphocytes
A T lymphocyte - WBC
Their surface is covered with receptors
Their receptors bind to antigens presented by APCs
Each T lymphocyte has a different receptor on its surface
When the receptor on the surface of a T lymphocyte meets a complementary antigen, it binds to it - so each T lymphocyte will bind to a different antigen
This activates the T lymphocyte - process called clonal selection
The T lymphocyte then undergoes clonal expansion - it divides to produce clones of itself. Different types of T lymphocytes carry out different functions
- T lymphocytes activate B lymphocytes, which divide into plasma cells
B lymphocytes are another WBC
They covered with proteins called antibodies
Abs bind to antigens to form an antigen-antibody complex
Each B lymphocyte has a different shaped antibody on its surface
When the abs on the surface of a B lymphocyte meets a complementary shaped antigen, it binds to it - so each B lymphocyte will bind to a different antigen
This, together with substances released from T helper cells, activates the B lymphocyte. Process called clonal selection
The activated B lymphocyte divides, by mitosis, into plasma cells and memory cells. This is another example of clonal expansion
- Plasma cells make more abs to a specific antigen
Plasma cells are clones of the B lymphocyte
They secrete loads of the abs, specific to the antigen, into the blood
These abs will bind to the antigens on the surface of the pathogen to form lots of antigen-abs complexes
What is cell signalling?
A cell amy release a substance that binds to the receptors on another cell - causes a response of some king in the other cell
Really important in the immune response because it helps to activate all the different types of WBC that are needed
What is the abs structure?
Abs are glycoproteins made of 4 polypeptide chains - 2 heavy chains + 2 light chains. Each chain has a variable region + a constant region
The variable regions of the antibody form the antigen binding sites. The shape of the variable region is complementary to a particular antigen. The variable regions differ between abs
The hinge region allows flexibility when the abs bind to antigen
The constant regions allow binding to receptors on immune system cells. The constant region is the same in all abs
Disulphide bridges hold the chain of the protein together
How do abs help to clear an infection?
Agglutinating pathogens - each abs has 2 binding sites, so an abs can bind to 2 pathogens at the same time - the pathogens become clumped together. Phagocytes then bind to the abs + phagocytose a lot of pathogens at once.
Neutralising toxins - abs called anti-toxins can bind to the toxins produced by pathogens. Prevents the toxins from affecting human cells, so the toxins are neutralized. The toxin-abs complexes are also phagocytosed.
Preventing the pathogen binding to human cells - when abs bind to the antigens on pathogens, the may block the cell surface receptors that the pathogens need to bind to the host cells. Means the pathogens can’t attach to or infect the host cells
What is the primary response?
Whena pathogen enters the body for the 1st time, the antigens on its surface activate the immune system.
The primary response is slow because there arent many B lymphocytes that can make the abs needed to bind to it
Eventually the body will produce enough of the right abs to overcome the infection. Meanwhile the infected person will show symptoms
After being exposed to an antigen, both T and B lymphocytes produce memory cells. These memory cells remain in the body for a long time
Memory T lymphocytes remember the specific antigen + will recognise it a 2nd time round. Memory B lymphocytes record the specific abs needed
The person is now immune
What is the secondary response?
If they get it again the immune response is quicker and stronger
Clonal selection happens faster. Memory B lymphocytes are activated + divide into plasma cells that produce the right abs to the antigen. Memory T lymphocytes are activated + divide into the correct type of T lymphocytes to kill the cell carrying the antigen
Gets rid of pathogen before symptoms show
