immunity Flashcards
antigen
molecule which trigger and immune response
phagocyte
white blood cell which carries out phagocytosis
2 types of immune response
humoral and cellular
cellular response (cell mediated)
t-cells and other immune system cells - doesn’t involve antibodies
humoral response
b-cells, clonal selection and monoclonal antibodies
where do t-cells mature
thymus gland
where do b-cells mature
bone marrow
t-cells respond only to antigens presented on…
a body cell
stages of response of t-cells to infection
1) pathogens invade body cells/are taken in by phagocytosis
2) phagocyte places antigens from pathogen on its cell-surface membrane
3) receptors on specific helper t-cell fit exactly onto antigens
4) attachment activated t-cell to divide rapidly by mitosis, producing clones of genetically identical cells
5) cloned T cells then - develop into memory cells
- stimulate phagocytes to engulf pathogens by phagocytosis
- stimulate B cells to divide and secrete antibodies
- activate cytotoxic T cells
how do cytotoxic T cells work?
produce protein called perforin that makes holes in cell-surface membrane - making it permeable to all substances therefore causing it to die (generally against viruses)
stages of response of B cells to infection
1) surface antigens of invading pathogen are taken up by the B cell
2) B cell processes the antigens and presents them on its surface
3) helper T cells attach to the processes antigens, activating B cell
4) B cell is activated to divide by mitosis to produce clones of the plasma cell
5) cloned plasma cells produce and secrete specific antibody that fits exactly to the antigens surface
6) antibody attached to antigens and destroys them
7) some B cells develop into memory cells –> secondary response
clonal selection
only the B cells that for an antigen-antibody complex is selected to divide into plasma cells
plasma cells
clones of selected B cells with complimentary antibodies to pathogen’s antigen
specific immune response stages
- ## phagocytes which have digested pathogen display the antigens on their cell surface membrane - becoming antigen presenting cells
4 main stages of the immune response
- phagocytosis
- t-cell activation
- b-cell activation and plasma cell production
- antibody production
how does HIV and AIDS work
- virus invades T ells and uses enzymes and ribosomes to replicate
- eventually so few T cells will be left that the immune system cannot respond to stimuli = AIDS
how do antibodies inactivate antigens (4)
- neutralisation - bind to viral binding sites and coat bacterial toxins
- coagulation of antigens - stuck together in clumps
- precipitation of soluble antigens
- activation of complement - tags foreign in cells for destruction by phagocytosis and complement
ELISA test method
1) HIV antigen bound to bottom of well in well plate
2) patient blood plasma cell sample added - HIV antibodies bind to antigens on plate
3) plate washed to remove unbound antibodies
4) antibody 2 is added with enzyme attached to it
5) binds to HIV antibody
6) well washed
7) solution added containing a substrate - reacts with enzyme to produce coloured product = positive result
exopeptidase
hydrolyse peptide bonds at the END of an amino acid chain
endopeptidases
hydrolyse peptide bonds inside an amino acid chain
antibody
proteins with a specific binding site, produced by B-cells
lymphatic response to self cells
[in fetus and bone marrow]
- lymphocytes collide almost exclusively with self cells although some will have receptors complimentary to body cells
- these either die or are suppressed before they differentiate into mature lymphocytes, therefore dont appear in the blood
d. non specific defence mechanisms
response which is immediate and is the same for all pathogens
specific defence mechanisms
response which is slower and specific to each pathogen
