Immunology Flashcards
define what an antigen is
a foreign molecule - usually a protein - that stimulates an immune response, resulting in the production of a specific antibody
which types of molecules does the body class as ‘non-self’? (4)
pathogens
transplanted cells
abnormal body cells
- owing to viral infection
- having become cancerous
toxins
“antigens will have a _________________________________ that is complementary to an _____________ or ____________ of an immune cell”
specific tertiary structure
antibody
receptor
“the immune system can be divided into two broad arms that provide a ______________ and ______________ response”
non-specific
specific
what occurs in the non-specific response of the immune system?
phagocytosis
what can phagocytes do? (2)
- distinguish between cells that display self antigens and those that display non self antigens
- destroy any cell presenting non self antigens through phagocytosis
describe the process of phagocytosis (5)
- phagocytes engulf pathogen
- this forms a vesicle called a phagosome
- phagocytes contain lysosomes, which fuse with the phagosome
- hydrolytic enzymes hydrolyse the pathogen
- exocytosis releases this debris
what occurs in the specific response of the immune system?
phagocytosis
then
antigen presentation
explain what antigen presentation is (2)
- when exocytosis occurs, the phagocyte keeps the attachment proteins
- it will then display these as its own antigens on its cell surface membrane
“the specific response can then be further divided into the _____________ response and the _____________ response”
cellular
humoral
explain the cellular response (4)
- initiated by antigen presentation
- t helper cells have a receptor that has a complementary shape to the antigen
- upon binding to the antigen, the t helper cells become activated and divide by mitosis
- they will then release cytokines
what three things does the release of cytokines trigger to happen?
- stimulates b cells to divide by mitosis
- stimulates phagocytes
- stimulates cytotoxic t cells
what type of cells do cytotoxic t cells target? (2)
- virally infected
- cancerous
how do cytotoxic t cells operate? (2)
- upon binding to antigens, they release perforin which makes a hole in the cell surface membrane
- the cells will then undergo apoptosis (cell death)
explain the humoral response (4)
- b cells can either be stimulated directly by the antigen binding to it, or by the release of cytokines
- they will divide by mitosis (“clonal expansion”)
- some will differentiate into plasma cells
- some will become memory cells
what do plasma cells do?
produce and release large quantities of monoclonal antibodies into the blood
what do memory cells do? (2)
- persist in the blood for years
- help to mount a faster immune response upon re-infection
which part of the humoral response is the primary response, and which part is the secondary response?
primary response
the differentiation into plasma cells
secondary response
the differentiation into memory cells
define what monoclonal antibodies are?
have the same tertiary structure produced by identical or cloned plasma cells
what are monoclonal antibodies an example of?
a quaternary protein
list the structural features of a monoclonal antibody (2)
- 4 polypeptide chains (2 heavy and 2 light) joined together by disulphide bridges
- two antigen binding sites
describe the function of an antibody (3)
- form an antigen-antibody complex
- ‘clumps’ the antibodies together (agglutination)
- this marks the antigens and helps attract phagocytes to the site of infection
what can a vaccine typically contain? (2)
- a dead or weakened form of the pathogen
- a specific antigen or antigens
how does the stimulation of memory cells help upon re-infection with the actual pathogen?
- they help coordinate the secondary response
- produces a higher concentration of antibodies AND faster
define herd immunity
some individuals, despite being unvaccinated, are also protected if the rate of immunisation is high in a population
define antigen-variability
where some pathogens can vary their antigens to evade detection by immune systems
list the negatives of vaccines (3)
- they are a drug; may have side effects
- harms may occur to animals during animal testing
- even if they show positive effects in animal testing, it doesn’t mean they will have the same positive effect in humans
define active immunity
an individual’s own body producing the antibodies and memory cells
define passive immunity
pre-made antibodies received from elsewhere that are put into the body
what procedure can monoclonal antibodies be used in?
why are we able to use them in these?
medical diagnosis
such as pregnancy tests
involves attaching a dye/stain
- because they can be made in the laboratory as artificial antibodies
what is the purpose of an elisa test?
to detect a specific antigen in a sample through the use of monoclonal antibodies
describe the elisa test (6)
- monoclonal antibodies fixed to the bottom of the well
- sample (potentially containing an antigen) is added to the well; will bind to the antigen-binding site on the antibody
- well is washed with water; to remove any unbound antigen
- second monoclonal antibody is added; attached to an enzyme; also complementary to the antigen
- well is washed again
- substrate is added
what is the result of an elisa test if an antigen is present within the sample? (2)
- the enzymes will convert the substrate to a different coloured product
- this colour change is a positive result
what would a positive control of the elisa test be?
the sample definitely has the antigen
what would be a negative control of the elisa test?
the sample definitely does not have the antigen
HIV: features (4)
- RNA genome
- reverse transcriptase; allows production of a copy of DNA from viral RNA
- genome is surrounded by a capsid
- lipid envelope contains attachment proteins
which cells specifically does HIV bind to?
t helper cells
CD4 receptors
describe the process of HIV replication (7)
- attachment proteins bind to CD4 receptors on t helper cells
- viral RNA and reverse transcriptase enter the cell
- reverse transcriptase converts viral RNA into DNA using host nucleotides
- viral DNA moves into the nucleus and is inserted into the host cell genome
- transcription of HIV DNA into HIV mRNA which is translated to produce HIV proteins
- infected t helper cell starts to assemble new virus particles (virions)
- virus particles are released from the t helper cell
“over time, the number of t helper cells _____________ as a result of HIV infection”
decreases
how do antibiotics work? (2)
- by preventing bacteria from synthesising murein cell walls or by directly damaging the cell wall
- some antibiotics also inhibit binary fission by preventing DNA replication and protein synthesis
