third line of defence (specific/adaptive immunity) Flashcards
when is the third line of defence activated?
when the first two are overcome
why does the adaptive immune response have tolerance to self cells?
ask labrooy
why does the adaptive immune response have immunological memory?
because memory T and B cells are produced.
why is the adaptive immune response specific?
because cells/antibodies have receptors that are specific to each antigen
what “test” must happen before b and T cells become naive?
if they don’t recognise self antigens/don’t respond to non-self antigens, they are eliminated via apoptosis; if they pass they’ll go to the lymph nodes where they’ll be activated
cell mediated adaptive immunity involves…
T cells
t cells recognise ______ pathogens
intracellular
describe t cell development
precursor cells develop in bone marrow then migrate to thymus where they become naive t cells.
describe t cell receptors
formed by 2 pp chains forming the antigen binding site
which can antigens can t cells repsond to?
only those physically linked to MHC self markers on the surface of other cells
define: antigen presenting cells
cells that move antigens to their surface and then display these antigens to other immune cells.
examples of antigen presenting cells?
dendritic cells and some phagocyes
wehre are dendritic cells usually found?
skin, lining of airways, gut
how do dendritic cells work?
Engulfs pathogens via phagocytosis and degrades them; but in the cytoplasm, they retain some peptide fragments from degraded pathogens, forming anitgens.
Antigens are then linked to class II MHC molecules in cytoplasm and then transferred to the cell surface.
Then, the dendritic cells go to the nearest lymph nodes and present them to naïve helper T cells.
what cell markers to helper t/cytotixic t cells have?
CD4vsCD8
how do helper t cells work?
antigens of antigen presenting cells bind to naive helper T cell receptors - activates, proliferates;
releases cytokines which enables diviision of cytotoxic T cells and B cells
how do cytotoxic t cells work?
when a cell is infected, its foreign antigens will be attached to MHC class I markers
Cytotoxic T cells with complementary receptors will bind to angiten, activating it, and when it receives Th cell cytokines it will divide.
THey release perforin and granzyme B, inducing apoptosis
what is the humoral adaptive immune response?
B cells, and their antibodies that they produce
humoral adaptive immune response acts on _________ pathogens
extracellular
define: antibodies
directly identify and bind to extracellular foreign antigens, either neutralising them or tagging them for destruction.
how are antibodies produced?
by B cells
where can antibodies be present
in solution in blood/lymph, in secondary lymph organs or as surface receptors on B cells.
how do antibodies work?
o Binding to surface antigens on pathogens, preventing them from binding to/infecting self cells
o For bacterial toxins, they bind toxin/venom, preventing them from binding to/effecting self cells.
o Binding to antigens on pathogens which tags them for destruction. Eg:
Complement proteins are activated by antibodies on surface of pathogens which can lead to formation of MACs
This binding opsonises them, making them more susceptible to elimination by phagocytes
describe structure of antibodies
2 light and 2 heavy chains, joined by hinge region consisting of disulphide bonds which gives antibody flexibility, helping it fit with antigen
constant region and variable region, consisting of an antigen binding site
describe IgG
- IgG is the main antibody in blood
- Passive natural immunity – passes placenta, in breast milk
- Activate macrophages and complement system
- Against viruses
describe IgM
- First antibody to appear at infection, defends until enough IgG is formed
- IgM is made up of 5 antibodies. Activates macrophages and complement system c
describe IgA
- Present in saliva, tears, sweat, mucous membranes, breast milk and bowel fluid - protects surfaces
- Against viruses
2 antibodies
describe IgE
- Activate mast cells which release histamines - therefore a key factor in allergic reactions + immune reactions to parasites
- Immune reactions to parasites
describe IgD
- Present on the surface of B cells and plays a role in the induction of antibody production.
- Activate basophils and mast cells
where do B cells develop?
bone marrow
deifne: clonal selection theory
explains how large numbers of antibodies for a specific antigen are produced at a given time when initially there are only a few B cells with these specific antibodies.
define: clonal selection
in lymph nodes, when antigen meets B cell with complementary antibodies (at antigen binding sites) on surface and binds to it.
define: clonal expansion
binding of antigen to its B cell. This activates it and initiates cycles of cell division, making clones of B cells.
what happens druing clonal expansion?
activated by helper T cell
takes about a week for sufficient numbers to be produced
differentiated into short lived plasma cells or long lived memory B cells
effect of memory B cells?
when the body encounters the pathogens again, a more rapid/strong immune response will occur – more antibodies will be produced, more quickly.
o This is the purpose of vaccinations
