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Immunoglobulins
- 5 classes
- Ig A
- Secretory-
dimeric
- has SC that
protects in harsh
enviroment of
secretions
- has SC that
protects in harsh
enviroment of
secretions
- 2 subclasses
IgA1/A2
- Serum-monomeric
- Secretory-
dimeric
- Ig D
- Very low serum
concentrations
- Found on lymphocyte
surface
- Function
unclear
- Very low serum
concentrations
- Ig G
- Most abundant Ig in
plasma
- It has 4
subasses-IgG1/G2/G3/G4
- Efficient at triggering
complement and
phagocytosis via Fc
receptors
- Only antibody to cross
placenta to foetus
- Predominant
antibody in 2nd
response
- Most abundant Ig in
plasma
- Ig M
- Only in plasma and
secretion too large to
enter tissue
- Pentamer, joined by J
chains and disulphide
bridges
- Heavy chains has
5 domains
- good at agglutinating
particles e.g viruses, efficient
at activating complement
- Predominant antibody
in 1st response
- Only in plasma and
secretion too large to
enter tissue
- Ig E
- Extra C domain
- Associated with
allergic response
- Protects against
parasites
- Extra C domain
- Ig A
- Structure of antibody
- Light chains have 2
types- Lambda and kappa
- Fold up into 2
domaians-VL and CL,
each domain made of 2
Beta sheets linksed b y a
disulphide bridge
- Fold up into 2
domaians-VL and CL,
each domain made of 2
Beta sheets linksed b y a
disulphide bridge
- Heavy chain determines the
class of the antibody
- Fold into 4(5)
domains-VH,
CH1,CH2,CH3 (CH4)
- Fold into 4(5)
domains-VH,
CH1,CH2,CH3 (CH4)
- Light chains have 2
types- Lambda and kappa
- Fab- responsible for binding the
antigen
- Fc-reponsible for effector
function (clearance mechanisms)
- How are antigens
recognised?
- 3 hypervariable loobs
(CDR) in each variable
domain (VH & VL) form the antigen
binding site
- Antibody recognises structural
epitopes on the antigen
- Binds antigen with non-
covalent interactions
- 3 hypervariable loobs
(CDR) in each variable
domain (VH & VL) form the antigen
binding site
- Effect of Antibodies
- Blocking of entry
to pathogens
- Antibody binds to virus preventing it
binding with receptors so preventing
fusion event
- Antibodies against adhesion bind to
bacterial and prevent colonization
and therefore uptake
- Antibody binds to virus preventing it
binding with receptors so preventing
fusion event
- Neutralisation of
toxins
- IgG and IgA bind to
solube toxin preventing
them from binding to
cellular receptors and
poisoning the cell
- IgG and IgA bind to
solube toxin preventing
them from binding to
cellular receptors and
poisoning the cell
- Activation of classical complement pathway
(IgM or Ig G) which leads to bacterial cell
lysis
- IgM binds to antigens on bacterial
surface, adopt staple form. C1q complex
binds to IgM and activates C1r which
cleaves and activates serine protease
- IgG bind to antigens on bacterial
surface. C1q cmplx binds to at
least 2 IgG molecules. This
activates C1r which cleaves and
activates serine protease
- IgM binds to antigens on bacterial
surface, adopt staple form. C1q complex
binds to IgM and activates C1r which
cleaves and activates serine protease
- Bacterial
opsonisation
- 1) Bacterial is coated in complement
and antibody
- 2) When complement bind to
receptor and the antibody
binds to the Fc receptor on macrophage membrane the
bacteria is phagocytosed
- 3) Macrophage
membrane fuse forming a
phagosome
- 4) Lysosomes fuse with hagosome
and release enzymes that degrade
the bacteria
- 1) Bacterial is coated in complement
and antibody
- Fc mediated clearance through
cross-links
- Aggregation of antibody on
bacterial surface allows cross-llinking
of Fc receptor and activation of
macrohage, leading to
phagocytosis and destruction
- Aggregation of antibody on
bacterial surface allows cross-llinking
of Fc receptor and activation of
macrohage, leading to
phagocytosis and destruction
- Blocking of entry
to pathogens
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