Unit 7 Antibodies I Structure and Function Flashcards
term antibodies is used in context of
antigens eg an antibody to antigen such as bacterium
term Ig is used when
to emphasize antibodies are globulin proteins produced by immune system
Ig are made up of
one pair of identical heavy chains and light chains
each chain is divided into
constant (C) and variable (V) regioons
what is variable region
high degree of variations among Ig. where the ABS is located (specificity)
what is constant region
same/constant among class of Ig (eg all IgM have same heavy chain constant region)
constant region is associated with
biological fn that could be unique to particular Ig class
light chains are further divided into
2 domains VL and CL
heavy chains are further divided into
4 domains Vh Ch1 Ch2 Ch3
eg the antigen binding site can be represented as
VL + Vh
enzyme papain cleaves Ig molecule into 3 fragments:
2 Fab and 1 Fc
composition of the 2 Fab fragments
VL Cl Vh and CH1 domains
composition of 1 Fc fragment
Ch2 and Ch3
enzyme pepsin cleaves Ig into
1 F(ab’)2 fragment (contains intact ABS) and 1 pFc’ fragment
constant region could contain (3)
- receptors for complement
- site that interacts w/transport protein in placenta to antibodies (IgG only)
- receptors for macrophages, granulocytes or mast cells
IgG (and C3b) can act as _ to do what
opsonin. help macrophage capture pathogen more easily
Ig are classified into 5 classes according to
constant region of heavy chains
Ig classes
IgG (four subclasses) IgA (2)
IgM, IgD, IgE
what is hypervariable region
variable regions of light (VL) and heavy chains (Vh) which contain ABS
features of IgG
most common in blood, major Ab of 2nd immune response, opsonin, when complexed w/Ag activates classical complement pathway, agglutinate antigen, pass through placenta passive immunity
IgG through placenta is what type of immunity
naturally acquired passive immunity
features of IgA
in seromucous secretions, saliva colostrum etc
structure of secretion IgA
2 IgA joined (dimer) together by joining chain
list benefits of secretory IgA
naturally acquired passive. lower incidence of GI and respiratory infections among breastfed
features of IgM
pentamer. activate classical complement, first Ig that appears in primary immune response. effective agglutinating Ab
IgM as a monomer found on
membrane of mature B lymphocytes. acts as cell surface receptors for antigens
why is IgM so effective an agglutinating
multple ABS allows attachment of many antigen
features of IgD
cell surface receptors for antigens on B cells
features of IgE
scarce in peripheral blood, w/eosinophils defend against parasitic worms, w/basophil or mast cell responsible for allergy
how is in vitro test of Type 1 allergy performed
checking serum level of total IgE or allergen specific IgE
effect of eosinophil binding to Fc of IgE
frustrated phagocytosis against big worm ->release granules of destructive enzymes
major fn of antibody (humoral) immune response (5)
neutralization, opsonization, activation of classical complement, agglutination, antibody dependent cell mediated cytotoxicity ADCC
what is neutralization (anti-adhesion)
block attachment of microorganism to susceptible cells (viral). block binding of microbial products such as toxins to target cells
what is opsonization
phagocytes are more effective in capturing extracellular Ag when coat with IgG
activation of classical complement by forming of Ab-Ag complex leads to
chemotaxis, inflammation, opsonization, and formation of MAC
agglutination is helpful how
increased number of antigens can be phagocytized when agglutinated
what is antibody dep. cell med. cytotoxicity ADCC
PMNs, macrophages, NK cells have receptors for constant region of Ab. when bind to Ab attached to org can kill them more effectively
primary vs secondary humoral response
primary generated following first encounter of antigen. secondary generated after in subsequent exposures
what is lag or latent phase
stage where no antibody is detected in blood/plasma
what is seroconverson
from sero -ive (no Ab detected) to sero +ive (Ab detected)
testing during lag/latent phase gives what results
false -ive. infected but pathogen-specific Ab not detectable
what is log phase
antibody titre (level) increases exp
what is paired sera
serum taken during acute (illness/lag) and convalescent (recovered/log) phase to see evidence of infection
what is plateau phase
when antibody titre reaches max and stabalizes
what is decline phase
Ab is catabolized and returns to lower level
