Antibody Structure and Function Flashcards
what are the two regions of an antibody?
the constant and variable regions
what are the 2 chains in an antibody?
the light and heavy chains
what holds the chains of an antibody together?
disulphide bonds
T/F the 2 light chains / the 2 heavy chains are identical to each other (both light are the same and both heavy are the same)
true
gene rearrangement in antibodies typically occurs in what region?
the variable region
why does gene rearrangement occur in the variable region and not the constant region?
because it is the region that binds to the antigen and if the constant part was changed, it would change the function of the antibody
can the heavy chains be functional without the light chains attached?
no
what are the 2 forms of light chains found in humans?
kappa and lambdid
can you have a kappa light chain on one side and a lambdid light chain on the other?
no
compare/contrast lambdid and kappa light chains
same function, slightly different constant region
what is the FAB region? where is it located?
antigen binding region; at top ends of Y structure
what is the FC region? where is it located?
effector function region; at bottom of Y structure
what happens if the FC region is changed?
class switch
what region defines the class of the antibody?
the FC region
describe the roles of FAB and FC in terms of an incoming protein
FAB recognizes it and the FC region chooses what to do about it
T/F each class of antibody has a unique FC region and unique function
true
which class(es) of antibodies are monomers?
IgD, IgE, IgG
which class(es) of antibodies are dimers?
IgA
which class(es) of antibodies are pentamers?
IgM
the structure of a pentamer can fold so that ___ stick up
FC regions
antibodies in a pentamer are connected by what type of chain?
J chain
do antibodies kill?
no, but they help other things kill
what are the 4 functions of antibodies?
- opsonization for phagocytosis
- fixing the complement
- blocking attachment
- neutralize toxins
what is the role of opsonization for phagocytosis?
facilitates uptake of bacteria by neutrophils/macrophages by creating a “candy coating” around bacteria
the complement cascade results in ___
MAC attack (membrane attack complex)
what is the function of MAC attack?
pokes holes in cells
the complement cascade is initiated by the ____ pathway
classical (antibody involved)
what are 3 requirements for fixing the complement?
- 2 antibodies must be involved
- they must be appropriately spaced apart
- both must have FAB region down on cell surface
a molecule called ___ (which has many different arms) will bind only to the FC region
C1
how many C1 molecules are needed to fix the complement?
2
why do antibodies need to be a specific distance apart to fix the complement?
the C1 is not flexible to conform to bind at whatever distance apart the antibodies are
the complement cascade includes everything from C__ to C__. Which are most important in killing bacteria?
1-9 ; C5-C9
why are C5-C9 the most important in killing bacteria?
they form a complex that makes a hole in the lipid bilayer, leading to osmotic flow into cell and lysis (MAC)
how can antibodies block attachment of viruses, some bacteria, and extracellular protazoa?
FAB regionbinds to protein on surface of virus, preventing the virus from being able to bind due to exposed FC region of attached antibody q
how do antibodies neutralize toxins?
bind to toxins, preventing them from binding to any toxin receptors
antibodies can also aggregate toxins into groups called ___
immune complexes
immune complexes can be removed by cells in the ___ and __ (organs)
liver and spleen
what is the most common class of antibody?
IgG
what are the 4 functions of IgG?
- fixes the complement well
- great at candy coating for phagocytosis
- blocks attachment well
- neutralize toxins
what is the only antibody class to pass through the placenta to provide early protection?
IgG
what is ivIg? why does it exist?
intravenous Ig agammaglobulinemia; no antibodies in the blood
IgM makes up __% if the Ig pool
10
what are the 3 functions of IgM?
- great at fixing complement
- great at blocking attachment
- good at blocking toxins
why is IgM good at blocking attachment and blocking toxins?
because it is so big
why does IgM fix complement so well?
its FC regions stick up making antibodies exact distance apart to fix C1
why is IgM not able to opsonize for phagocytosis?
5 congregated FC regions will not fit into FC receptor
is IgM or IgG made first? why?
IgM, because it does not require a class switch
IgA makes up __- % of the Ig pool
15
IgA protects what areas of the body?
mucous membranes in lungs and gut
what are the 2 functions of IgA?
- blocking attachment
2. neutralizing toxins
why cant IgA fix complement well?
the FC regions of the dimer are unavailable
why cant IgA opsonize for phagocytosis?
dimer cant fit into FC receptor
why is IgA good at neutralizing toxins?
the dimer aggregates well
what are 2 reasons why someone might have high levels of IgE?
- they are atopic (many allergies)
2. a parasitic infection with roundworms
IgE binds to ___ on mast cells
FcER ( FC epsetion receptor )
what functions are IgE good at?
none of the typical, because it is bound to the mast cell and not availble
IgD makes up ___ % of the Ig pool
basically zero
what is the function of IgD?
not well known, but maybe involved in B cell activation
what are monoclonal antibodies and their purpose?
antibodies typically produced in a lab
monoclonal antibodies are almost always which Ig? why?
IgG; long lifespan
finding monoclonal antibodies in circulation can help diagnose ___
cancer originating from expansion of single b cell
extracellular bacteria are fought by __ and __
innate immune system and antibody
intracellular bacteria are fought by __ and are not dependent on __
cell-mediated immunity; antibody
what is the role of the complement if an extracellular bacteria has never been seen before?
binds directly to bacteria and kill it a bit
what is the role of c3b if an extracellular bacteria has never been seen before?
activates the alternate pathway that activates neutrophils to eat it
the alternate pathway will also respond to ___ if an extracellular bacteria has never been seen before
toll-like receptors
toll-like receptors cause killing by (2)
- reactive oxygen and nitrogen interediates
2. superoxide, h202, NO
do macrophages have defensins?
no
what is the role of the dendritic cell if a bacteria has never been seen before?
take up antigen for presentation at the lymph nodes to activate the adaptive immune response
what will the antibodies do if an extracellualr bacteria has been seen before?
will bind, opsonize and fix the complement
what is post strep glomerulonephritis?
decomposition of antibody/antigen complex in the kidney glomeruli leads to destruction of the kidney tissue
decomposition of the antibody/antigen complex in the kidneys leads to activation of __ and __
- frustrated phagocytosis
2. activation of complement
frustrated phagocytosis is used to kill ___ infections
parasitic
what is post strep rheumatic fever?
IgG response to strep A antigen cross reacts with the heart, damaging the valves and myocardium
Th-1 is involved in the __ response
inflammatory
can IFN -y activate infected macrophages?
not very well
when IFN-y activates uninfected macrophages, they release ___ and ___
IL-1 and INF
what is the role of TNF in fighting infection?
brings more macrophages to the site
what are the main cells affected by HIV?
CD4+ T helper cells
in the long run, what can happen to a granuloma if there are not enough CD4+ t cells at the site?
it can degrade and release the infection
