The Immune System Flashcards
What triggers an immune response?
The detection of a pathogen with non self antigens
What is an antigen?
A molecule found on the surface of cells causing immune responses
Describe the first stage of the Immune response (phagocytosis)
Cytokines attract phagocytes to pathogens
Phagocyte recognises pathogen as non self.
Phagocyte engulfs pathogen by moving cytoplasm around it
This forms a phagosome (vesicle with pathogen in)
Lysosome fuses with phagosome
Forms phagolysosome
lysosome releases enzyme that digests pathogen
(Next stages only in macrophage)
antigens combine with MHC
anitgens are then presented on cell surface membrane
Known as an APC
What happens after phagocytosis?
T lymphocyte has receptors on surface
These receptors bind to the antigens on the APC
When receptor on lymphocyte finds a complementary antigen, it binds to it
This means the T lymphocyte is activated
Process called clonal selection
The activated T lymphocyte undergoes clonal expansion
Dividing to form different types of T lymphocytes
What are the 3 types of T lymphocytes made from clonal expansion?
T helper cells - release interleukins that activate B lymphocytes
T killer cells - attach to and kills cells infected with the virus
T regulatory cells - stop response once virus is gone and stops immune system from attacking self cells.
How do B lymphocytes work?
Activated by interleukins released from T helper cells. These B lymphocytes divide by mitosis into plasma cells and B memory cells. The plasma cells release the specific antibodies to go find the pathogens and disable them by forming an antigen-antibody complex.
What are plasma cells?
Identical to the B lymphocyte with complementary antibodies to invading antigens.
They secrete loads of antibodies into the blood
What happens when an antibody binds to a complementary antigen?
An antigen-antibody complex is formed.
Describe the structure of an antibody?
two ‘heavy’ (long) polypeptide chains bonded by disulfide bonds to two ‘light’ (short) polypeptide chains
Each polypeptide chain has a constant region and variable region
Contains two antigen binding sites - allowing agglutination
What is agglutination?
Antibodies have two binding sites so can bind to two antigens on different pathogens at once. This allows antibodies to agglutinate pathogens together (clump) so that it’s easier for phagocytes to phagocytose a lot of pathogens at once.
How do antibodies help to clear an infection?
Agglutinating pathogens
Neutralising toxins
preventing the pathogen binding to human cells
Why is the secondary response faster?
when same pathogen enters the body again, memory B lymphocytes with antibodies complementary to the antigens on the pathogen are already in the body so can easily and quickly divide into plasma cells to release more antibodies.
