Adaptive Immunity, B and T structure, receptors, and antibody Flashcards
what is the difference between B and T cell receptors?
B: contains antibody of defined specificity
T: specific for peptides derived from APC degraded antigen presented on MHC molecules
what is the structure of a B cell receptor?
antigen binding specificity expressed with co-receptor involved in signa transduction
2 identical heavy chain
2 identical light chain
when is B cell activated?
when antigens bind
(antigen can bind to one or two b cells which connects them)
what are the coreceptor molecules for B cell receptor?
Iga (alpha), igb (beta)
transduce signals via ITAMS
antibody has two forms:
membrane bound form and secreted Ig form
what is the membrane bound form of antibodies?
serves as a signal receptor on B lymphocytes
what is the secreted Ig form on antobodies?
do not have cytosolic segment, instead hydrophobic segment
where are antibodies made?
B lymphocytes or plasma cells (highly differentiated B lymph that are specialized in secretion of antibodies)
most antibodies are: (structure)
divalent
two symmetrical binding sites to allow cross linking
what is special about the hinge region of the antibody?
proline rich area that allows extension
what bond hods antibody structure together
disulfide
(has domains that are aso hed together by disulfide bonds)
what possibilities make up the light chain?
kappa or lambda
what possibilities make up the heavy chain?
Mu
gamma
alpha
delta
Epsilon
how are immunoglobulins categorized?
which heavy chain is used
what are the domains of an antibodies?
–variable light and heavy
–constant light
–CH1,2,3
what is in the N terminal of amino acids?
antigen binding sites (Fab)
what is at the C termina of antibodies?
Fc, crystallization (mediates effector activities)
antigen bind to ______ derived by _______
antigen bind to the Fab fragment derived by the papain digestion from an antibody
(bind to determent from variable light and heavy chain)
describe antigen antibody binding
one end of the Fab fragment (paratope) directly interacts with HA’s surface burying several amino acid residues. together these amino acids define the epitope
what is a hypervariable region?
within the variable region, these AA make the closest contact with antigen at antigen binding sites
-these AA give the antibody its specify
what is another name for hypervariable region?
complementary-determining regions, CDRs (1,2 or 3)
what bonds form between antigen/antibody?
non-covalent
(van der waal, electrostatic, hydrogen, hydrophobic)
describe the fit of antigen/antibody bonds?
require a close stearic fit
closer the fit the higher the affinity (binding specificity)
what is antibody affinity?
strength of bond between singe antigenic determinant and singe combining site on antibody (may be mutivalent)
what is the difference between affinity and avidity?
affinity is strength of individual bond
avidity is strength of multiple bonds
what are t cell receptors structurally similar to?
immunoglobulin domains
what is the structure of a T cell receptor?
α and β, each has Variable and Constant regions
Variable regions have three CDRs forming the peptide-specific binding site
Constant regions each contain transmembrane regions
TCR αβ recognizes and binds:
both antigen-derived peptide and MHC to which peptide is bound
what are some co-receptors on T cells?
– CD3 contains ITAMs that transmit signals to the cell
– CD4 and CD8 function in increasing the avidity of peptide binding by TCR
– CD28 engages CD80 or CD86 on APC to fully activate a naive T cell
what is phosphorylated on ITAMs?
CD3 (T cells) and Igα/β (B cells)
Phosphorylated tyrosines serve as docking points for
adapter molecules
what is clonal selection?
- When the B/T cell receptors engage with that antigen, the B/T cell becomes activated (also called “selected”)
- Activation results in proliferation, producing a large number of clones
what are the 5 types of immunoglobulins?
IgM
IgA
IgE
IgG
IgD
(good chart on 111)
What is the shape of IgG?
monomer
where is IgG found?
blood steam and tissue fluid
what is special about IgG?
it can cross placenta (not IgG2)
what are the actions of IgG?
agglutinates
* precipitates
* opsonizes
* mediates ADCC
* activates complement
* neutralizes
what is opsonization?
IgG anchors bacteria to phagocytes for easier digestion
what is antibody dependent ceII mediated cytotocity?
IgG anchors bacteria for NK ceIIs
what is the shape of IgM?
pentamer
what is special about the composition of IgM? (2 things)
has J chain that connects its parts
H chain had extra domain (CH4)
where is the membrane form of IgM expressed?
monomer version expressed on the ceII surface of early B ceIIs to serv ad BCR
what are the jobs of IgM
- Agglutinates (has 5 binding sites)
- Activates complement.
- First immunoglobulin produced in an immune response
- First immunoglobulin produced in infants
- Provide early protection
- Produced in response to T-independent antigens
- Most efficient antibody for agglutination precipitation and complement fixation
- Low affinity
- Poor neutralization
What is special about IgD?
not secreted, surface bound to mature B cells
what does IgD do?
signal receptor
triggers further differentiation of B lymphocyte
where are IgA found?
externa secretions, colostrum, mil, saliva, mucus, sweat, tears
what does IgA do?
agglutinates
neutralizes
which immunoglobulins have extra domains?
E & M
what is IgE associated with?
allergies and sensitivities
what occurs during the antigen independent stage?
generation of vast repertoire of B/T cells with out antigen telling specifics
Diversity within the antibody repertoire is achieved by:
- Selection of many mini-gene segments
- Recombination to join the randomly selected mini- gene segments
- Addition & deletion of nucleotides during joining of mini-gene segments
- Association of different light and heavy chains to form binding sites
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