Antibodies Flashcards
(33 cards)
how many isotypes of antibodies are there and what are they?
IgG, IgA, IgM, IgD, IgE
describe the polypeptide structure of Abs
they are comprised of 2 H and 2 L chains. One L chain is bound via disulfide bonds to one H chain, and the H chains are likewise bound via disulfide bonds. The H and L chains are identical on a given Ab. A given B cell only produces 1 type of Ab.
what determines the isotype of an Ab?
the type of heavy chain. there are 5 that correspond to the 5 isotypes (IgG, A, M, D, E)
what is allelic exclusion in B cells
B cells encode a large amount of DNA regarding of L and H chains, but a B cell only produces one type of Ab. During development, allelic exclusion occurs when a recombined H and L chain are made correctly and expressed.
once 1 chromosome has properly recombined, the other chromosome is repressed. furthermore, further recombination on the active chromosome is also repressed
how many types of L chains are there?
there are two types
describe variable and constant regions on the heavy and light chains
both the H and L chains have intrapolypeptide (within the same chain) disulfide bonds that form loops with distinct properties.
on the heavy chain, the 3 loops on the C-terminal end of the Ab are Constant regions. All Abs of the same subtype have identical C regions. This region is called the Fc region, and they determine the effector function of the Ab. The CH2-CH2 region forms the hinge of the Ab and is a binding site for complement. The final loop on the N-terminal side is the Variable region, which works with the VL region to form the Ag binding site
the light chain also has a V and C site. the N terminal sides of both chains with the V regions are together called the Fab. the C-terminus of the light chain also has a constant region
how does TCR and Ab binding differ?
Abs bond to native structures and can bind more than peptides
TCRs must bind MHCs that have processed peptide fragments on them
epitope
the smallest unit of an Ag that an Ab can bind
multi-determinant Ag
most Ags have multiple epitopes, and thus can be recognized by different Abs
Ab valence
the maximum number of Ags it can bind
Ab affinity
the tightness with which an Ab binds
Ab avidity
the combination of valence and affinity. having multiple sites (valence) is beneficial to keeping an Ag bound
IgG
IgG is dimeric and the most abundant Ig in the blood. It provides the bulk of immnunity to blood-borne Ags and is the only Ig to provide passive immunity to the fetus.
there are 4 subtypes: 1-4
IgM
found in 2 locations: in the blood and on the membrane
when expressed on the surface, it is a dimer and acts as the B-cell receptor
in the blood, it is expressed as a 5 4-chain units. additionally the J chain is necessary for the combination of 5 subunits. It is the first Ab produced in the immune response, and it binds with low affinity but has a combined 10 binding sites (high avidity)
IgA
present in serum and secretions
in the serum, it exists as a monomer
in secretions, it exists as a dimer, along with the J-chain, and secretory component. the SC helps with transepithelium journey. it is found in musous, milk, and other secretions
IgD
only present in low amounts in the circulation. Mostly found in mature naive B cells (along with IgM- both specific for the same Ag). Differences in IgD can be used to differentiate effector types and developmental stages
IgE
found in low levels in the sera- mostly associated with amplifying inflammation, allergic reactions, and protection from worms. Bind to Fc receptors on mast cells which cause the release of inflammatory compounds
allotypes
differences in the AA sequence of Abs that are inhereted. these are minor polymorphic differences
idiotype
the set of epitopes on the V region of an Ab
how many gene loci are there for antibodies?
there are 3- one for K light chain, on for lambda light chain, and one for H chain
describe VDJ recombination
It begins at the loci for the H chain, which contains ~100 V regions, ~27 D regions, and ~6 J regions. The first step is that a D and a J region will move together to form a DJ region. Then, a V region will join them, forming a VDJ region. These recombinations are random, and are the source for Ab diversity. Downstream are the C regions, usually u for IgM. the DNA is transcribed and the introns (nonVDJ material) is excised.
This combination is uninterrupted in mature B cells
A similar process occurs for the L chain, except they do not have D regions. It can occur either at K or lambda C loci, but not both. It tries at the K region first.
how does an Ab become membrane bound or released?
it depends where the poly A tail is added. There is a hydrophobic AA sequence that would become the transmembrane sequence, but if it is poly Aed before that sequence, it will be released. These exons are separate from the C regions
What are the CDR1-3.
these are found on the heavy and light chains in the V regions. they are hypervariable and go a long way in determing specificity, especially CDR3. 1 and 2 are in the V region, while 3 is determined partly by V, and also by D and J.
what is imprecise joining
when the V, D, and J regions move, they may cause the deletion or addition of a nucleotide, changing the structure
