Immune system - P1 Flashcards
define antigen
- Molecules which recognised as non-self/foreign by the immune system,
stimulate an immune response and lead to the production of antibodies
why is antigen specificity important
- Pathogens (disease causing organisms)
- Cells from other organisms of the same species
- Abnormal body cells
- Toxins released from bacteria
define pathogen
disease causing microorganisms
triggering an immune response
describe phagocytosis
- phagocyte attracted to bacteria by chemicals/recognise antigen on pathogen as foreign
- phagocyte engulfs/ ingest pathogen
- pathogen in vacuole/vesicle
- lysosome fuses with vesicle/ vacuole + releases lysozymes (hydrolytic enzymes)
- pathogen digested
describe the cellular response - t lymphocytes
- T lymphocytes recognises antigen presenting cells after phagocytosis (foreign antigen)
- Specific T helper cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly by mitosis to form clones which:
a) Stimulate B cells for the humoral response
b) Stimulate cytotoxic T cells to kill infected cells by producing perforin
c) Stimulate phagocytes to engulf pathogens by phagocytosis
examples of a specific response
humoural
cell-mediated
what are antibodies
quaternary strucutred proteins
secreted by B-cells
bind to specific antigen to form antigen-antibody complex
describe + explain how structure of antibody relates to its function
primary structure - sequence of amino acids in polypeptide chain
determines folds in secondary structure
determines tertiary structure + placement of ionic, hydrogen + disulfide bonds
quaternary structure- 4 polypeptide chains
2 heavy chains, 2 light chain
specific shaped variable region - different in each antibody - forms complex with complementary antigen
allows antigen-antibody complex to form
how do antibodies work to destroy pathogens
binds to 2 pathogens at a time, at variable region
forming antigen- antibody complex
enables antibodies to clump together - agglutination
phagocyte binds to antibody + phagocytoses many pathogens at same time
what does the hinge region enable
antibody can bind to antigen/pathogen at different distances apart
why will an antibody bind to a specific antigen
- antibodies’ variable region has specific sequence of amino acids
- so shape of binding site
- is complementary to only the antigen
- forming an antigen-antibody complex
describe the humoral response
- clonal selection
a) specific b-cell binds to antigen presenting cell, stimulated by t-cells
b) divides rapidly by mitosis to form clones - some b-cells divide into plasma cells
- some b-cells divide into memory cells
what do plasma cells do
secrete large amounts of specific antibody
for primary response
what are memory cells for
secondary response
so specific antibody can be produced quickly
what is the primary response
when the pathogen enters for the first time
describe the primary response
antibodies produced slowly + in lower concentration
not many b-cells to make required antibody
t-cells need to activate b-cells to make antibodies
so symptoms occur
describe the secondary response
produces antibodies at higher rate + conc
b + t memory cells present
so b cells undergo mitosis quicker/clonal selection
how does antigen variability create difficulties for effective vaccines
new vaccines against disease need to be developed more frequently
vaccines may not be developed or hard to develop against disease
may experience disease more than once
explain effect of antigen variability on disease
- Change in antigen shape (due to a genetic mutation)
- Not recognised by B memory cell → no plasma cells / antibodies
- Not immune
- Must re-undergo primary immune response → slower / releases lower concentration of antibodies
- Disease symptoms felt
Explain the effect of antigen variability on disease prevention (vaccines)
- Change in antigen shape (due to a genetic mutation)
- Existing antibodies with a specific shape unable to bind to changed antigens / form antigen-antibody complex
- Immune system i.e. memory cells won’t recognise different antigens (strain)
what is a vaccine
injection of antigens
from attenuated pathogens
stimulating formation of memory cells
can lead to symptoms
Explain how the use of vaccines can provide protection for individuals against disease
- Normal immune response but the important part is that memory cells are produced
- On reinfection / secondary exposure to the same antigen, the secondary response therefore produces antibodies faster and at a higher concentration
- Leading to the destruction of a pathogen/antigen (e.g. agglutination and phagocytosis) before it can cause harm / symptoms = immunity
Explain how the use of vaccines can provide protection for populations against disease (herd immunity)
- Large proportion but not 100% of population vaccinated against a disease – herd immunity
- Makes it more difficult for the pathogen to spread through the population because…
- More people are immune so fewer people in the population carry the pathogen / are infected
- Fewer susceptible so less likely that a susceptible / non-vaccinated individual will come into contact with an infected person and pass on the disease
difference between active + passive immunity ; exposure to antigen
active - exposure
passive - no exposure
