Adaptive Antigen Recognition in the Immune System Flashcards
Where are plasma cells (activated B cells that secrete Abs or memory cell) primarily found?
Lymphoid Organs
The highly variable chains in BCRs are NH-terminus of H and L chains (Vh and Vl), what are they in TCRs?
NH-terminus of Valpha and Vbeta
What are the antigens, diversity, signaling and effector functions of BCRs (Ig)?
Macromolecules like lipids/proteins
Unique specificity
IgA and IgB (signaling)
Fc region of Ab is effector
What are the antigens used for TCR, how do they signal, and what are their effector functions?
Antigens are peptides presented by APC (linear short AA)
Signaling by CD3 and (Zeta) subunit?
No effector function
Antibodies are used interchangeably with immunoglobins, most Abs are found in the third slowest migrating group of globulins, known as?
Gamma gobulins (followins B and Alpha)
Antibodies have four polypeptide chains- two light (L) chains and two heavy (H) chains bound together by what?
Disulfide bridges
Both H and L chains are divided into V and C regions, V regions contain the Antigen binding site and the C region determines?
The fate of the Ag
If an antibody is cleaved, it will yeild two Fab fragments (fragment Ag-binding) and a what?
Fc fragment (fragment crystallized) responsible for effector functions
Papain is a enzyme that cleaves IgG before the heavy chain constant area into what?
2 Fab fragments and an Fc fragment
Which enzyme will generate a single bivalent antigen-binding fragment (F(ab’)2) from IgG?
Pepsin by proteolysis of IgG
There are 5 different types of H chains known as IgM,D,E,A,and IgG. There are two different light chains, how many different light chains can each Ab have?
Abs can only have one of the two different light chains
how are polypeptide loops of 110 amino acids created on Abs?
By H and L intrachain disulfide bridges every 90 amino acid residues
What are some cells that recognize, bind and adhese to cells, that are part of the immunoglobin superfamily?
TCRs, MHC 1/2, CD4, CD28, and ICAM-1
For IgG, the Ag-binding sites are formed by Vl and Vh domains, the heavy chain C regions end in tail piecesand Fc/compliment receptor binding sites are in the heavy chain constant regions. IgM on B cells (membrane bound) has a C terminal transmembrane and cytoplasmic portion that anchor the molecule in plasma membrane, what does it have one more of than IgG?
IgM has one more Ch4 domain
Where are hinge regions on antibodies located and what do they do?
They are located between Ch1 and Ch2 domains, allowing flexibility to bind 2 surface antigens close or far away
What are the five classes or isotypes of immunoglobulins (Ig)?
IgG, IgA, IgM, IgE, IgD
Abs formed in the primary response soon after Ag has lower affinity to stick to Ags. Abs produced from memory response have…?
A higher affinity (1000x higher) than primary response
Valence of an Ab is the maximum number of antigenic determinants it can react with… since IgG has two Fac regions, it can bind two molecules of Ag. It will have a valence of?
Valence of 2
Avidity gives a measure of overall strength of Ab-Ag complex and is dependent on what two things?
- affinity of Ab for Ag
2. Valence of both Ab and Ag
What are the steps in making monoclonal Antibodies?
- Splenocytes from immunize mouse with known Ag are isolated
- Isolated cells fused with meyloma via polyethylene glycol to form hybrids (myeloma cells do not secret own Ig)
- Hybrid cells placed in selection medium (HAT) that permits survival of only immortilized hybrids
- HAT consists of hypoxanthine, aminopterin, thymidine
Myeloma cells lack hypoxanthine-guanine phosphoribosyl transferase (HGPRT) used for purine salvage pathway in most cells, and aminopterin blocks de novo purine synthesis and have to rely on a salvage pathway resulting in what?
Only hybrid cells survive in HAT medium
TCRs are composed of alpha and beta chains, each chain containing one variable and one constant region (just like Ig’s) what is in the Variable region of each TCR chain?
3 hypervariable complementarity-determining regions (CDR), each corresponding to a loop in the V domain
Since the cytoplasmic regions are too small to transduce signal from the TCR, CD3 and zeta(?) proteins are on either side and serve as?
Signal transducing subunits of the TCR complex
CD4 has four EC Ig-like domains (single chain) with a hydrophobic trasnmembrane region and a highly basic cytoplasmic tail (38AA long). What chains compose CD8?
CD8 alpha and beta chains
Like CD4 coreceptors, CD8 have a hydrophobic transmebrane region and a basic cytoplasmic tail that is (25AA long different than 38 in CD4). How many extracellular Ig domains does it have?
Only 1 as compared to 4 in Cd4
What are the different stages of B cell development?
Stem cell Pre-B cell (surrogate light chain) Immature/Naive B cell (IgM only) Mature B cell (both IgD and IgM) Activated B cell Plasma cell/Antibody secreting cell
What are the chromosomes related to the BCR genes, including Ig H chain locus, Ig k chain locus, and Ig(lambada) chain locus?
H at chromosome 14
k at chromosome 2
lambda at chromosome 22
What are the chromosomes associated with TCR genes including TCR B chain locus and TCR A chain locus?
B at chromosome 7
A at chromosome 14
There are mutltiple different exons that encode different domains of the C regions for Ig and TCR.. this allows?
The generation of diverse BCRs and TCRs
What are the three unlinked gene groups at different chromosomes which encode immunoglobulins?
one for u H-chain
one for k Lchain
one for lambda L chain
Allelic exclusion occurs in B and T cells, which means only one light chain and one heavy chain is expressed in a single B cell.. this means?
Either parental or maternal alleles are expressed! However, they will be expressed equally since there are many different types of B cell and T cell receptors
What is the major mechanism of epitope-specific diversity of BCR and TCR?
DNA chromosomal rearrangement which will switch up the location of variable chains.
What 3 mechanisms of rearrangement can alter the expressivity of genes?
Somatic Recombination
mRNA splicing
Junctional diversity
RAG 1 and RAG2 proteins initiate V(D)J recombination by making double strand breaks, which are repaired by homologous recombination and nonhomologous end-joining (NHEJ). What are Rag-mediated breaks exclusively resolved by?
NHEJ
There are many different types of variable, diversity and joining segments in each gene which allows for?
multiple different types of receptors and genes being made…heavy chains are most diverse(?)
BCR diversity acheived by heavy chain.. has 4 separate gene segments; V, D, J, C with multiply copies of each. In a b cells all copies are randomly deleted besides for one in each segement… this leads to?
Leading to each B cell generating its own VDJ sequence, making them all very different
During developmental stages of B and T cells only, Recombination-activating genes (RAG)s are expressed which do what?
Encode enzyme performing recombination of BCR and TCR during the proces VDJ recombination
What is the difference between and immature B cell DNA and a mature B cell DNA?
In mature cell, each DNA segment (VDJ) is present as a single copy, in immature there are many copies
In BCR recombination, D and J are chose and DNA between them is deleted first. Second, a V segment is chose and DNA between V and DJ is deleted. What happens third?
A C is chosen and DNA between VDJ and C is delete.
The chance to produce a ‘productive rearrangement is about 10%, there is a test that can be done to check. When confirmed by the test, what happens?
the competition between paternal and maternal H genes is over and recombination of other segments is stopped
Once Vh recombination in heavy chain is productive thenB cell proliferates and then will start light chain. which light chains do not have the D segment (diversity)?
K and lambda
The recombination rules for the light chain is the same for heavy chain, with the final result being one kind of Vh and one kind of Vl…… meaning that the B cell can?
recognize any Ag possible
What are the difference in copies of VDJ between the alpha and beta chains of TCRs?
Alpha chains have more V and J copies while Beta chains have less V and J copies, but have two D copies
For TCR gene rearrangement, what chain goes first?
B chain then A chain
What does terminal deoxynucleotidyl transferase (TdT) do in junctional diversity?
It adds or removes nucleotides to the exposed ends of the V, D, or J genes before they are reunited
VDJ recombination alone woulf not be enough to recognize all antigens possible, so junctional diversity mediated by terminal deoxynucleotidyl transferase (TdT) with do what?
Increases the diversity of TCRs from 3x10^6 to 10^16 and diversity of BCRs from 10^6 to 10^11
Junctional diversity is generated at points between joining genes and results from the loss of nucleotides through the actions of exonucleases and from the addition of N and P necleotides. What generates P nucleotides?
Asymmetric opening of hairpin loops by RAG ( which have a palindromic appearance)
What does the opening of the hairpin loop produce ?
short, self-complimentary single stranded extensions that can be incorporated into junctions or can be removed
TdT adds N nucleotides after P nucleotides are added, resulting in?
finished product of junctional diversity
What are the different Ig DNA and RNA throughout each step in maturation of B cells?
Stem cell: germline DNA
Pro-B: germline DNA
Pre-B: recombined H chain
Immature B: Recombined H and light chain (IgM)
Mature B: Alternative splicing is done (IgM/IgD)
There are many checkpoints in lymphocyte development that can only be passed if they complete the proceeding step. The first checkpoint is after the production of?
the first polypeptide chain of two-chain Ag receptor is completed
What is the second checkpoint in lymphocyte development?
Follows the production of the second polypeptide chain of the Ag receptor is completed
The selection process eliminates potentially harmful…?
self-reactive lymphocytes due to lack of both chain rearrangment processes being completed
Pre-ag receptors deliver signals to continue on, also known as pre-BCRs and pre-TCRs. The pre-Ag receptors contain only one polypeptide chain present in a mature Ag receptor and a ?
surrogate receptor chain
Pre-BCRs contain Ig u heavy chain and pre-TCRs contain?
TCR B chain
Ig heavy chain is first receptor gene to be rearranged, once this is done the gene express the u heavy chain protein and assemple the what?
pre-BCR
T cell that make a productive TCR B chain gene arrangement synthesize TCR B chain protein and assemple the what?
Pre-TCR
30% of B/T cells make productive inframe rearrangements of the Ag receptor gene. If out of frame rearrangements are made then…?
pre-ag receptors are not expressed and cells do not receive survival signal and undergo apoptosis
The second checkpoint has positive and negative selection for some cells, how is a cell preserved through positive selection?
If they are function pre-ag receptors they express genes encoding the second chain and if they are successful and express useful Ag receptors they go through positive selection
Positivie selectrion of T cells ensures the maturation of CD8 or CD4 t cells whose receptors dont recognize self-ags but can do what?
recognize MHC molecules class I or II
What is the main role of negative selection at the second checkpoint of lymphocyte maturation?
They eliminate harmful t cells and alter harmful b cells who Ag receptors bind strongly to self Ags present in the thymus/bone marrow
Harmful T cells w high affinity for self ags are eliminated by apoptosis (clonal deletion) while B cells are given a second attempt in Ig gene rearrangement, by a process called?
Receptor editing, if this fails, B cell dies (called clonal deletion)
B cells that develop from fetal liver-derived stem cells differentiate int B-1 lineage, B lymphocytes that arise from Bone marrow precursors after birth give rise to?
B2-lineage
B1 cells express limited BCR diversity because TdT is not expressed in fetal liver (NO JUNCTIONAL DIVERSITY). The large number of B1 cells are found as?
a self-renewing population in peritoneum and mucosal sites
B1 cells, called natural antibodies, contribute to most serum IgM during early phases of infection. What do IgM most often react with?
microbial polysaccharides and lipids and oxidized lipids
B2 cells develop in bone marrow and relocated to spleen once they are immature b2 b cells. What two things can immature B 2 B cells differentiate into?
either marginal zone (Mz) Bcells or mature follicular (FO) B cells
FOB2 cells are recirculating lymphocytes while MzB2 cells are abundant in the spleen but can also be found in?
Lymph Nodes (localized in splenic marginal zone and respond to blood borne Ags)
FOB2 cells respond to protein Ags in a T-cell dependent manner and undergo Ig isotype switching and affinity maturation. Only FOb2 cells upon t cell dependent activation can develop into….
long lived- plasma cells or memory cells
MZ B cells are in the marginal sinus in the spleen and lymph node, like B1 cells they have BCRs w limited diversity. Mz B cells respond rapidly to,,?
blood borne microbes and turn into short lived IgM secreting plasma cells
Thymus epithelium has cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells (mTECs=stroma). Thymocytes evolve to mature T cells featuring cell differentiation antigens (CDs) which characterize phenotypically distinct stages known as…?(3)
Double-negative (DN)
Double-Positive (DP)
Single-positive(SP)-based on expression of the coreceptors CD4 and CD8
Stroma or mTECs express genes coding for organ specific proteins, also known as promiscuous gene expression (PGE), what role doe PGE play?
Plays a role in central tolerance to self-antigens which prevents autoimmunity
DP cells are programmed to undergo apoptosis unless a rescue signal is delivered via TCR. 95% of DP cells dont signal and undergo…?
death by neglect or apoptosis
Some DP cells are able to bind MHC with mild avidity, allowing them to be saved from apoptosis. TCR signals DP maturation to SP thymocytes… also known as?
CD4+CD8- or Cd4-Cd8+ single-positive cells (POSITIVE SELECTION)
Negative selection (clonal deletion) is the process by which high-avidity TCR selfpeptideMHC ligation induces cell death… Negative selection occurs in the?
Thymic medulla
If TCR and CD28 are engaged in binding, DP/SP thymocytes undergo apoptosis. Stroma cells express self-peptide-MHC and costimulatory molecules….?
CD80/CD86
When CD80/86 is High in medulla than cortex, this suggests?
medulla as the more favorable environment for negative selection
Elimination of self-ractive thmocytes through clonal deletion requires a complete representation of tissue specific Ags (TSAs) in the thymus. Control of TSA expression is controlled by genes such as?
the Autoimmune regulator (AIRE)
