immune response Flashcards
what is a phagocyte
white blood cells that destroy pathogens
what happens in phagocytosis
phagocytes recognise and bind to antigen on pathogen
phagocytes engulf pathogen and enclose in a vesicle
lysosome fuses to vesicle, releasing lysozymes
digested pathogen removed by exocytosis
the phagocyte presents antigens on surface (APC)
what happens in cellular response (T cells)
specific helper T cell bind the APC
T cell is activated to divide rapidly by mitosis
helper T cells release cytokines which stimulate cytotoxic T cells
cytotoxic T cells release perforin, destroying infected cells
what happens in humoral response (B cells)
specific B cell binds to antigen and is activated by cytokines
B lymphocyte divides by mitosis, differentiating into plasma cells and memory cells
plasma cells produce and release antibodies
memory cells circulate the blood and produce plasma cells more quickly later
what is antigenic variability
the antigens on the surface of viruses differ with each strain due to mutation so memory cells don’t recognise them
describe the structure of antibodies
have a quaternary structure made up of four polypeptide chains held together by disulphide bridges
variable region - different in different antibodies
antigen-binding site - complementary shape to the antigen - specific
constant region - same for all antibodies .
hinge region - provides the antibody with flexibility
describe the mechanism antibodies work by
bind to antigens to form antigen-antibody complex neutralise pathogens by clumping them together (agglutination)
phagocyte engulfs them
how does HIV infect cells
attachment protein bind to CD4 receptor on helper T cells
capsid containing RNA is released into cell
reverse transcriptase makes complementary DNA strand using viral RNA as template
viral DNA produces viral proteins, assembling new viruses
new viruses bud from T cell, destroying them and infecting other cells
how does AIDS develop
HIV destroys T cells
B cells and cytotoxic T cells aren’t activated
weakened immune system so susceptible to disease
how is HIV treated
no cure but can use antiretroviral drugs to slow HIV replication and there are preventative measures (safe sex, clean needles)
what are monoclonal antibodies
identical antibodies produced from a clone of the same B cell
how are monoclonal antibodies made
- mouse injected with antigen so produces specific plasma cells
- plasma cells are extracted
- fused to myeloma (tumour cell), forming hybridoma cells that rapidly divide
what are monoclonal antibodies used for
pregnancy tests, drug tests, drug treatment
what is the ELISA test
enzyme linked immunosorbent assay
a diagnostic technique that detects the presence of antibodies / antigens
what are the steps of an ELISA test
monoclonal antibodies bound to container
sample added to container
if they possess complementary antigens → bind to antibodies in container
washed to remove unbound antigens
secondary antibody attached to enzyme added to solution
binds to antigen
washed to remove unbound secondary antibody and enzyme
substrate for enzyme added
substrate hydrolysed if enzyme present → colour change occurs indicating positive result
what is the primary immune response
when infected by pathogen for the first time
non-specific and the specific immune response
slow
experience symptoms
memory cells produced
what is the secondary immune response
when re-infected in the future
memory cells recognise antigen and divide
quick
weak or no symptoms
what is a vaccination
introduction of dead/weakened pathogen into an organism with the intention of making them immune to a disease
how do vaccines work
vaccine contains specific antigens
stimulates an immune response
on second exposure, pathogen is destroyed before symptoms develop due to memory cells
what is active immunity
when the body makes its own antibodies after being stimulated by antigen
natural ie getting ill
artificial ie vaccination
take a while to develop but long lasting as memory cells created
what is passive immunity
when given antibodies produced by another organism
natural ie breastfeeding
artificial ie antibody injections
immediate but short lived as memory cells not created
