L6: Antibodies & Antigens Flashcards
another name for abs
immunoglobulins
most abs are found in the _____ slowest _______ group of globulins, named ____ globulins for the third letter of the greek alphabet
third slowest migrating group of globulins
named gamma globulins
effector properties of abs
- reduce damage to host from inflammatory response
- organized t cell response
- opsonization
- activation of complement
- toxin neutralization
- direct antimicrobial activity
- immunomodulation
basic structure of abs
basic unit = 4 polypeptide chains – 2 light L chains
—2 heavy H chains
how are abs chains bound together?
by covalent disulfide bridges
and
noncovalent interactions
both H and L chains are divided into ?
V and C regions
V region
contain the ag binding site
C region
determine the fate of the ag bound in the V region
abs can be proteolytically cleaved to yield?
2 Fab fragments
1 Fc fragment
Fab fragments
fragment ag-binding
2 short arms of the Y
Fc fragment
fragment crystallized
responsible for effector functions
stem of the Y
IgG is cleaved by enzymes ____, where on the ab?
papain
at the 3-way junction of the Y shape
Papain digestion of IgG
allows separation of 2 Fab fragments and Fc fragment
Fc receptors then bind Fc fragment
proteolysis of IgG by pepsin
pepsin generates a single bivalent antigen-binding fragment = F(ab’)2
Stem + (2 arms still connected)
types of H chains
there are 5 dif types
greek letters or
IgM, IgD, IgG, IgE, IgA
types of L chains
2 types
k and gamma
each with a MW of 23 kDa
each Ab unit can have only what type of L chain?
k or y
cannot have both
both H and L chains have intrachain _______ bridges every _____ amino acid residues, which create ?
disulfide bridges
90 aa
polypeptide loops/domains of 110 amino acids (these domains are named by location)
Ig superfamily proteins
a large group of cell surface soluble proteins
are involved in the recognition, binding, adhesion processes of cells
Ig superfamily types
T cell receptor MHC molecules CD4 coreceptor CD28 ICAM-1
secreted IgG
- ag binding site formed by Vl and Vh domains
- heavy chain C regions end in tail pieces
- complement and Fc receptor binding sites w/in heavy chain
membrane bound IgM on ___ cell
B cells
1 more Ch4 domain than IgG
C-terminal transmemb portion
cytoplasmic portion to anchor on memb
abs have great flexibility due to ?
hinges – the junction point of the Y
hinge region located between Ch1 and Ch2 domains
what is the importance of ab flexibility?
allows them to attach to widely spaced cell surface determinants or to closely spaced ones
how do abs recognize ags?
conformational determinant
linear determinant
neoantigenic determinant
conformational determinants
ab has selective binding for specific conformation of ag
so determinant is lost if ag is denatured
linear determinant
Ig binds to determinant in denatured protein only
or
Ig can bind to native and denatured forms
neoantigenic determinant
this is created by proteolysis
determinant near site of proteolysis
define abs affinity
the tightness of ag-ab binding is called affinity
dif abs will differ in their affinity for one ag
when the binding constant is higher ?
it is less likely the ab will dissociate from the ag
which abs generally have lower affinity for ags?
abs produced in the primary response soon after injection of an ag
which abs generally have higher affinity for ags?
abs produced by a memory response
association constants 1000x higher
when is affinity especially critical?
when the ag is a toxin or virus and must be neutralized rapidly at low titers
define valence of abs
the maximum number of antigenic determinants w/ which it can react
