immune system Flashcards
what is a pathogen?
a microorganism that causes disease
what is immunity?
the body’s ability to kill a pathogen before it causes any harm
what are the 2 types of white blood cell?
lymphocyte and phagocyte
what are the two types of lymphocyte?
T-Lymphocyte and B-Lymphocyte
why must white blood cells be able to distinguish between cell and non-self?
this allows the white blood cells to know what is part of your body, and what is not so that the body’s own tissues aren’t destroyed
what is used to identify cells as self or non-self?
the proteins on the cell surface
why are proteins used to identify whether cells are self or non-self?
they have a huge variability and the 3D (tertiary) structure is very specific
what is the immune system able to identify?
- pathogens (e.g. HIV)
- non-self material (e.g. cells from another organism)
- toxins
- abnormal body cells (e.g. cancer)
what is the name given to the protein which causes an immune response?
antigens
what issue may arise with the immune system, due to transplants?
the immune system may recognise the tissues as non-self, and therefore attack transplanted organs/tissues.
2 types of defense
specific and non-specific
2 types of non-specific defense
physical barrier and phagocytosis
2 types of specific defense
cell mediated response and humoral response
what type of cells are involved in cell-mediated response?
t-lympocytes
what type of cells are involved in humoral response?
b-lymphocytes
when a pathogen enters the body, how is the correct lymphocyte selected?
it already exists in the body, but must be stimulated to replicate
what do we mean by “correct” lymphocyte for a particular pathogen?
just as each pathogen has specific proteins on their surface that indicated what they are. the lymphocytes have complementary proteins which fit those of the pathogen
phagocytosis
engulfment of pathogens
phagocytosis (process)
- phagocyte recognises foreign antigens on the pathogen
- cytoplasm of the phagocyte moves around the pathogen, engulfing it
- the pathogen is now contained in a phagocytic vacuole
- a lysosome fuses with the phagosome and the lysozymes break down the pathogen
- the phagocyte presents the pathogen’s antigens-> it sticks the antigens on its surface to activate other immune system cells
t-cells/t-lymphocytes
another type of white blood cell; activated by phagocytes;
has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes, which activates the t-cell;
helper t-cells release chemical signals that activate and stimulate phagocytes and cytotoxic t-cells which kill abnormal and foreign cells;
also activate B-cells which secrete antibodies
b-cells/b-lymphocytes
another type of white blood cell; activated by T-cells;
covered in antibodies – proteins that bind with antigens to form an antigen-antibody complex;
each B-cell has a different shaped antibody on its membrane, so different B-cells bind to different antigens;
when the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it;
this, together with chemical signals released by helper T-cells, activates the B-cell (clonal selection); activated B-cell divides into plasma cells
plasma cells
identical to B-cells (clones);
they secrete loads of antibodies specific to the antigen – monoclonal antibodies – which bind to the antigens on the surface of the pathogen to form antigen-antibody complexes
antibodies
proteins – made up of chains of amino acids;
the specificity of an antibody depends on its variable region (binding site);
each variable region has a unique tertiary structure that is complementary to one specific antigen; antibodies have two binding sites – it can bind to two pathogens at the same time;
this means pathogens become clumped together – agglutination;
phagocytes then bind to the antibodies and phagocytose many pathogens all at once; this process leads to the destruction of pathogens carrying this antigen in the body
phagocytes
patrol the body, searching for invaders (non-self antigens);
ingest and destroy pathogens in phagocytosis
when the pathogen is engulfed, what is the vesicle called?
phagosome
what fuses with the phagosome?
lysosomes
what do the lysosomes contain and what do they do to the pathogen?
hydrolytic/digestive enzymes called lysozymes;
breaks down the pathogen
what happens after the pathogen has been digested in the phagosome?
the soluble products are absorbed into the cytoplasm of the phagocyte
When a pathogen enters the body it may be destroyed by phagocytosis. Describe how.
phagocyte attracted by a substance / recognises (foreign) antigen;
pathogen engulfed / ingested;
enclosed in vacuole / vesicle / phagosome;
(vacuole) fuses / joins with lysosome;
lysosome contains enzymes (lysozymes);
pathogen digested / molecules hydrolysed;
cell-mediated immunity
the response of T-Lymphocytes to foreign antigens presented on a body cell
what form do most antigens take?
proteins on the cell surface membrane
which white blood cell is involved in the specific immune response?
lymphocytes
where are the two types of lymphocytes made and matured?
t-lymphocytes: made in bone marrow, matured in thymus gland
b-lymphocytes: made in bone marrow, matured in bone marrow
what do T-Lymphocytes respond to?
the body’s own cells which have been infected;
cells from individuals of the same species (genetically different).
why can T-Lymphocytes identify invader cells from normal cells?
phagocytes present antigens of hydrolysed pathogens on their surface membrane;
body cells present viral antigens on their surface during infection;
transplanted cells have different antigens on their surface;
cancer cells are different, so present different antigens on their surface membrane
what is an antigen presenting cell?
a cell which presents antigens which are foreign on their cell surface membrane
which antigens will T-Lymphocytes respond to?
foreign antigens presented on the cell surface membrane
what are the stages of T-Cell response to infection by a pathogen?
- phagocyte ingests pathogen;
- pathogen’s antigens are placed onto the phagocyte’s surface membrane (becomes an APC)
- the receptors of a specific Th cell bind perfectly to the antigen being presented.
- this binding activates the Th cell to divide and produce many clones. (clonal expansion)
- these cloned cells specialise
in what way might cloned Th cells differentiate?
- develop into memory cells
- stimulate phagocytes
- stimulate B-cells to divide and secrete antibodies
- activate Tc cells (cytotoxic cells)
what chemical do cytotoxic (Tc Cells) produce?
perforin
how does perforin kill pathogens?
it perforates (makes little holes) in the membrane which makes it freely permeable, so it dies
what pathogens do Tc cells work best against? why?
viruses;
viruses only replicate when in a host cell; if the host cell dies, replication can no longer occur
primary immune response
when an antigen enters the body for the first time
slow; there aren’t many B-cells that can make the antibody needed to bind to it
person infected shows symptoms while the body makes enough of the right antibody to overcome the infection
after being exposed, both T-cells and B-cells produce memory cells which remain in the body for a long time
memory T-cells remember the specific antigen and will recognise it a second time (if it doesn’t mutate)
memory B-cells record the specific number of antibodies needed to bind to the antigen
person is now immune – immune system has the ability to respond quickly to a second infection
secondary immune response
at the second exposure, the immune system produces a quicker, stronger immune response
clonal selection happens faster
memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen
memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen
this response often gets rid of the pathogen before you begin to show symptoms
cellular response
the T-cells and other immune system cells that they interact with e.g. phagocytes
humoral response
the B-cells, clonal selection and production of monoclonal antibodies
what is meant by humoral immunity?
the second stage of an immune response, causing B cells to produce antibodies which dissolve into the blood and tissue fluid (the humor)
why are there millions of types of B-cells?
each one creates an antibody to respond to a specific antigen; the variations in antigens require a large number of different antibodies
what does the B-cell have on its surface to fit the foreign antigen?
a specific antibody that will only fit this antigen and vice versa
how is a B-cell stimulated to divide by mitosis?
an activated Th cell binds to the processed antigens on the B-cell to stimulate it to divide by mitosis, creating clones (clonal selection)
why are more than 1 type of B-Cell activated for each pathogen?
each pathogen typically has many proteins on it’s surface membrane, acting as antigens. they also produce toxins. all of these can stimulate B-cells to make clones
what are the antibodies created from B-cell clones described as?
monoclonal antibodies
what can the B-cell clones differentiate into?
plasma cells and memory cells
what do plasma cells do?
create a specific antibody
what do memory cells do?
they last a long time in the body, when they encounter the complimentary antigen to their antibody, they are stimulated to divide rapidly;
this creates lots of memory and plasma cells quickly, and therefore lots of antibodies are created quickly
why is the secondary immune response much faster and of a greater magnitude than the primary immune response?
the primary response relies on the activation of both the specific Th-cell and B-cells before antibodies can be released;
the secondary immune response needs only the B-memory cell to be activated, and there would be more of those in the blood
what is an antibody?
a protein created by a B-cell, it has two identical, specific, binding sites
what does an antibody do?
it binds to a specific antigen, which is complimentary to its specific binding site
what are antibodies made of? (basic structure)
they are made of 4 polypeptide chains
2 long (heavy chains) and 2 short (light chains)
what is the name given to the binding site of an antibody?
the variable region; this is due to it being specific to a particular antibody, so they are all different
what causes the variable region of an antibody to be different?
the sequence of amino acids that form a specific 3D shape
what do antibodies do to pathogens?
- cause agglutination through binding to two pathogens at once; many pathogens can be clumped together in this way
- they act as markers to stimulate phagocytosis
how are monoclonal antibodies used to treat diseases (specifically cancer)?
direct monoclonal antibody therapy and indirect monoclonal antibody therapy
how does direct monoclonal antibody therapy work?
- monoclonal antibodies are created which will attach to specific antigens on cancer cells
- these are given to the patient; they attach only to the cancer cell’s receptors
- this blocks the signals required to stimulate uncontrolled mitosis
how does indirect monoclonal antibody therapy work?
- monoclonal antibodies are created which will attach to specific antigens on cancer cells
- a cytotoxic (cell-killing) drug, or radioactive substance is attached to the monoclonal antibody
- these are given to the patient; they attach only to the cancer cell’s receptors
- this kills the cell
