Antibodies and Antigens Lecture Flashcards
Immunogenicity
the ability of a given molecule to induce an immune response
General characteristics that contribute to immunogenicity are
phylogenetic foreignness
chemical nature
size
complexity
route of uptake
host
Antigen
a molecule that binds specifically with an antibody of T cell receptor
Epitope
the actual part of an antigen that binds to an AB or T cell receptor binding site
Most antigens have multiple ______. These are called _______
epitopes
multivalent antigens
epitopes can be
repeated within Ag molecule or not
overlapping
formed by linear arrays of AAs
conformational (AAs not in sequence)
Neo-epitopes (exist/exposure after AG changes such as phosphorylation, protealysis)
Adjuvant
a compound that is given with an antigen when immunizing a host, to augment the immune response achieved
Abs are a family of millions of
structurally related glycoproteins
each unique Ab has a specific binding sites for pieces of
antigen (called an epitope)
Abs are produced by
B lymphocytes/Plasma cells
Abs are produced in two broad forms-
- bound to B cell membranes
- secreted soluble form
Abs bound to B cell membranes act as
B cell receptors for antigens
Abs secreted in soluble form are
free floating and able to bind Ag in plasma, mucosal secretions, interstitial fluids
When Abs bind to Ags they can
Remove the Ag
neutralize the Ag
kill organism expressing the Ag
Trigger ‘hypersensitivity’ reactions
Abs bind to Ags and remove the Ag by
precipitating it out or inducing phagocytosis
Abs bind to Ags and neutralize the Ag by
preventing a microbial enzyme from working or a virus from binding
Abs bind to Ags and kill organism expressing the Ag by
poking holes in them
Abs bind to Ags and trigger hypersensitivity reactions by
histamine release, immune complex activation of complement proteins
Antibody structure- two symmetrical branches made up of 2 identical ______ and 2 identical _____
light chains
heavy chains
One L chain is ______ to one H chain by ________ and other two H chains are attached to each other by _______
covalently attached
S-S bonds
S-S bonds
Both L and H chains are made up of
repeating homologous units
each Ab has identical combining sites to which the
NH2-terminal ends of both L and H chains contribute
Variable regions
regions that recognize epitopes and make the ab combining site
are specificity
The N-terminal lg domain of each L and H chain contains _ hypervariable regions called _____
3
complementarity determining regions (CDRs)
CDRs are ____ to the epitope
complimentary
Due to the way L and H chains fold, CDRs end up in the _______
hypervaraible loops, which come together
The hypervariable loops formed by the CDRs actually
extend from the surface of the Ab molecule to form the Ab combining site
the furthest and most variable CDR
CDR3- most highly involved in the actual binding
AAs outside of the CDRs can
contribute to the binding site but most of the time do not
The C-terminal end of the H and L chains are comprised of
Ig domains
but have very little variability
Constant regions are opposed to
variable regions
do NOT interact with the antigen/epitope
C regions of the H chains actually mediate
most of the biological functions of the antibody and the isotype of the Ig
H chain C regions are numbered
CH2, CH2, numbering from the NH2 terminus
Hinge region
between CH1 and CH2- allows flex and is of different lengths in different isotypes
Any given Ab has how many of each L chain C regions
2 K or 2 ^
never one of each
Abs can be expressed in
secreted or membrane forms
The membrane form of Abs is ONLY found on
the B cells that make that given Ab
Membrane forms of Abs differ in
AA sequence at the COOH terminus of the H chain C region
Secreted forms of IgG and IgE are
monomeric
The membrane forms of all isotypes is
monomeric
The secreted forms of IgA and IgM are
covalently bound multimers, joined through the tail pieces at the carboxyl ends of M and A H chains
IgM and IgA also have a _____ which is S-S bonded to the tail pieces for stabilization
J piece
Abs are
at least bi-valent
flexible
Ab membrane form is the
B cell receptor
Ab secreted form acts
throughout the body
Ab B regions combine with Ag in a
highly specific manner
Ab C regions of their H chains interact with
multiple cell types and soluble inflammatory molecules, which mediate effector function
Synthesis of immunoglobulins
synthesized on membrane bound ribosomes and glycosylated in the rough endoplasmic reticulum
Once assembled, immunoglobulins
move to golgi complex to undergo modifications of their carb molecules
Immunoglobulins are transported to plasma membrane in
vesicles and either and either anchored or secreted
Monoclonal
each B cell makes Abs of one specificity. These are all clones of each other
Polyclonal
Serum contains LOTS of Abs of millions of specificities because an animal contains millions of different B cells.
Affinity maturation
process that yields Abs that bind tightly to their Ag
Affinity maturation involves
subtle changes through somatic mutations in Ag-stimulated B cells that produce new V regions structures
B cells with higher affinity receptors are
selected by Ag becoming the most dominant
Abs can distinguish between
linear proteins determinants that differ by a single conserved AA in their sequence
Even is specificity is very high
eptitope might be part of multiple Ags
Cross reactions occur when
an Ab combines with multiple epitopes
when specificity is low
Affinity of an Ab is
the pure measure of the on/off rate between Ag and Ab combining site
Avidity is the term for
true, overall strength of attachment of an Ab to its Ag
Affinity + valency=
avidity
Types of common assays that use Abs
enzyme-linked immunoabsorbant assays
radioimmunoassays
hemagglutination assays
flow cytometry
immunohisochemistry
western blot assays
dipstic assays
