Chapter 4 sections 7-16 Flashcards
chapter 4 parts 2 and 3
flow cytometry
use of fluorescent labeled monoclonal antibodies to ID cells
Immunoglobulin diversity before B cells encounter Antigen
Germline configuration of gene segments encoding for Igs are inherited via egg and sperm
and encoded in gene segments on regions of chromosome 22,2,14
but only expressed in B cells following successful gene rearrangement
Occurs on chromosome 22,2 14
gene segments that code for Ig diversity that was inharerited via egg and sperm
Light chain formation via somatic recombination
2 options for Light chain gene formation
from the germline DNA lamda variable segments is selected
which is joined to
J segment and one of the constant segments
or
from the germline DNA kappa variable segments is joined to j segments and a constant kappa segment
Heavy chain formation via somatic recombination
2 options for Heavy chain gene formation
from the germline DNA 1 H variable segments is selected
1D segments
which is joined to 1J segments
and one of the Mu constant segments + the gene for the transmembrane component finally V and DJ segments are join
all the components of heavy chain gene
1 H variable segment +((1D segment+1J segment)+one Mu constant segment + transmembrane component)
all the components of light chain gene
1 lambda variable segment + 1 j segment + 1 constant segment
or
1 Kappa variable segment + 1 J segment + 1 constant Kappa segment
mu version of H chain results in
IgM production
somatic recombination
the process of choosing of one of many gene segments to form an exon that can be transcribed
how to find # possibility of type of chain kappa light chain lambda light chain heavy chain these are only present in B cells
(# of possibilities for Variable region) X (#of possibilities of J segments)
how many variations of diversity result from somatic recombination and combinatorial association
1,628,400 posiblities in the variable region alone aka tons of diversity
this impacts the hypervariable regions 1& 2
combinatorial association
when light and heavy chain bind together their impact on antigen binding
HV
hyper variablility
Recombination signal sequences (RSS)
directs somatic recombination, RSS that flanks the V and D and J segments there are 2 types
these provide a point for enzymes to cut and rejoin the gene segments
2 Types of RSS
hepatamer
and nonamer
these are separated by a 12 base pair segment or a 23 base pair segment
length of bp segment that separated the 2 types of RSS
12 or 23 bp length segments
V(D)J recominase
enzyme that clips out RSS segment and rejoins gene segments
this enzyme is only made in lymphocytes
enzymes associate with RAG1-2 gene to for RAG complex that forms DNA into a hairpin and then cleaves and rejoins it bringing V and j segments together
RAG-1 and 2
recombination -activating genes, these gene products and other enzymes associate to for RAG complex that forms DNA into a hairpin and then cleaves and rejoins it bringing V and j segments together
Junctional diversity
occurs when enzymes of RAG complex join the gene segments VD and J
palindromic nucleotides (P nucleotides)
nucleotides that are read the same forward and backward the RAG complex adds these P nucleotides by nicking one strand of DNA at the terminus
at Junction
enzyme can remove gremlin encoded nucleotides or TdT enzyme can add nucleotides that are not encoded in the Germline
N nucleotides
nucleotides that are not encoded in gemline
RAG forms
the hairpins and ceaved one strand of DNA
TdT
terminal deoxynucleotidyl transferase,
acts as addition of N nucleotides which were never germline
N=
nontemplated
Generation of junctional diversity
where mutations form, P nucleotides clipped and add nucleotides to J segment and now it have gained 2 more amino acids
Exonuclease’s
remove unpaired nucleotides, leaving gaps taht are later filled by actions of other enzymes involved in DNA editing.
Over all BCR diversity is generated as a product of
(somatic recombination + combinatorial association)X(Junctional diversity)= overall diversity =(4.8x10^13)
Junctional diversity increases the overall diversity by_______
3x10^7
Junction diversity impacts the ________ region
Hyper variable
A process similar to junctional diversicty occurs in _________ this is called ____________
T cells
functional TCR
SCID (sever combine immune defficency)
due to lack of RAG enzymes to form hair pin loos and cleave thus resulting in no functional T or B cells(have no receptors) this is a genetically aquired disorder
AIDS virus causes
due to lack of functional T cells(no receptors)
Alternative mRNA splicing
Joining of VDJ and transcription of them
results form translation of Transcribed VDJ
Surface expression of IgD and IgM of same specificity (same V region but different Constant regions)
the difference and similarity of IgD and IgM structure
both have differing constant regions but the same V region
only 2 antibodies expressed simultaneously on B cell surface
only two classes that are express on naive circulating B cells
only Classes that are expressed on circulating niave B cells (not yet encountered antigen)
IgD and IgM
Only antibodies expressed simultaneously on B cell surface
IgD and IgM both are membrane bound
Allelic exclusion
both light and heavy chains occurs so that a developing B cell only expresses an Ig of one specificity.
allowing for clonal selection to occur creating an antibody specific for pathogen
clonal selection
finding of specific antigen by B cell = affinity and causes B cell to mature to plasma cell which then releases cytokines to stimulate other B cell maturation
when B cell only expresses an Ig of one specificity
Allelic exclusion
B cell Ig receptors
are made in the ER and then associated with Ig Alpha and Ig Beta which assist in transport to surface.
the transmembrane portion is hydrophobic and can be imbedded in membrane
When antigen interacts with Fab region of Ig the transmembrane segments of the Ig are too short to send signals so it requires help to send intracellular signals by utilizing IgBeta and Ig Alpha which have longer cytoplasmic tails
IgAlpha and IgBeta
have longer cytoplasmic tails then B cell receptor so assist in intracellular signal tansduction
always paired with B cell receptor when receptor present
Diversification of Antibody occurs _____
after B cells encounter Antigen
Following B cell encounter with antigen
B cell starts changing into plasma cell and starts secreting large amounts of IgM and small amounts of IgD due to alternative splicing and processing of RNA (no change in DNA)
Difference between membrane bound Ig and secreted Antibody
membrane bound Ig has hydrophobic C terminus end
antibodies hydrophilic C terminus
Somatic hypermutation
the process that increases diversity in Ig after a B cell encounters its Antigen
Rate of random pint mutation is
1 per cell division, this is 1 million times more frequent than normal
When random point mutations occur in variable region of H and L genes(within a single nucleotide substation) it leads to
somatic hypermutation
CDRs
compliment Detemning Regions
where Random point mutations occur
somatic hypermutation targets
the rearranged gene segments encoding the variable region (aka occurs most frequently in variable region)
Immunization IgM and IgG levels
low levels of IgM are present within the first week of primary immunization
the second week there is a large increase in the amount of IgM and IgG appearas and is abundant
due to huge changes in receptors due to mutation to encounter and fight antigen/pathogen(from vaccine) this leads to a super high affinity antibody
Activation-induced cytidine deaminase (AID)
is the enzyme important in the process of somatic hypermutation and only is expressed in proliferating B cells
AID function
converts Cytosine to Uracil (uracil is only found in RNA so DNA repair enzymes replace the Uracil with 1/4 other DNA nucleotides)this leads to mutation due to this some of the newly expressed mutant Ig has a higher affinity which are then selection and become plasma cells
High affinity for antigen Mutant Ig on B cells leads to
selection and then maturation of these B cells to become plasma cells
Affinity maturation
antibody of progressively higher affinity for the antigen are then produced as the adaptive Immune response proceeds
a process of evolution that results in an improved product and can be achieved in a few days instead of a few years
allos the slow evolving human to keep up with fast evolving pathogens
Isotype
aka class switching
class swithcing
is dependent on AID and occurs only in B cells that are proliferating in response to the encounter of their antigen
Class switching consists of
DNA recombination of heavy cain constant region
but does not change the specificity of the V region but does result in excision of the perviously expressed heavy chain and insertion of new heavy chain
The heavy chain determines the _______ of the antigen
Class
does class switching change specificity of V region
no
what does Isotype switching change
swaps heavy chain in consent region for another thus changing the class so IgM switch to IgD
Paitents who lack AID
results in hyper IgM immunodeficiency
the Ig on B cells of patients who lack AId cannot under go somatic hypermutation or isotype switching
only have IgM in body no other antibodies to help fight
low affinity of IgM results in
high levels of IgM present to compensate for low affinity
Increased susceptibility to infection by pyogenic (pus producing) bacteria due to
AID low levels of IgM
also there is No IgA to protect MM
bond that holds IgM monomers together forming ______
a disulfid bonds and a J chain work together to hold 5 IgM monomers together to form a pentameric IgM creating potentially 10 binding sites
monomeric IgM contains
4 constant regions
Joining chain (J chain)
helps hold pentameric IgM together and Dimeric IgA
IgM affinity
low affinity binding site so more sites (petameric molecule) helps counter low affinity by increased # of sites
IgG affinity
High affinity bindind due to ionic switching thus IgG is less is abundents is nessicary then IgM
Different C regions on antibodies results in
different effector functions of Antibody classes
IgD, IgE, IgM are each a separate
class
IgA and IgG each have
sub classes with varrying affinity
IgA sub classes
IgA1 and IgA2
IgG sub classes and varying affinities *
IgG1>IgG2>IgG3>IgG4 these are numbered in terms of abundance in plasma i.e. igG1 is most abundant
IgG1
is the most abundant in serum
IgM function and property
neutralization
activation of complement system (best at this)
some is transported across epithelium
a little diffusion into extravascular sites
IgD function and property
no function or properties
IgG1 function and property
great to Neutralization Opsonization Sensitization for killing by NK cells a little sensitization of mast cells Activation of Complement system
IgG2 function and property
Neutralization
Activation of complement system
Transports across placenta
and major at Diffusion into extravascular sites
diffusion into extravascular sites facilitated by antigen
IgG1, IgG2, IgG3, IgG4
IgG3 function and property
neutralization opsonization sensitization for killing by NK cells sensitization of mast cells Activation of complement system Transport across placenta Difusion into extravascular sites
neutralization stimulated by this antigen
IgG (1,2,3,4)
IgG4 function and property
Neutralization
Opsonization
Transported across placenta
Diffusion into extravascular sites
IgA function and property
neutralization Opsonization activation of complement system transport across epithelium (dimer) Diffusion into extravascular sites (monomer)
IgE
Sensitization of mast cells
Diffusion into extravascular site
Transport across epithelium=
transport on MM
which is trasphers to baby via breast milk
IgG
Best neutralizing Antibodies belong to class
IgG(1-4) and IgA
Best Opsonizing antibodies belong to class
IgG1, IgG3, igG4 & IgA (
Sensitization for NK killing
igG1 and IgG3
Sensitization of mast cells
IgE, IgG1 and IgG3
Complment activation
IgM, IgG(1,2,3) and IgA
transports across epithelium
dimeric IgA and some IgM
Transports across placenta
IgG 1,2,3,,4
diffusion into extravascular spaces
all IgGs
Monomeric igA
IgE and very little IgM
least abundant in serum
IgE and IgD
IgM
First antibody produced during a primary IR and begin with low affinity so have multiple binding sites (10) which increase avidity
a good complement activator not a great opsonin
doesn’t cross easily into extravascular spaces
cannot cross placenta
avidity
overall strength of binding of entire andtibody and antigen
affinity
is the strength of binding at one site
if a newborn has IgM
this indicates and intrauterine infection (this IgM was produced by baby and is its own)
IgG
most abundant form in blood and lymph
small and flexible can cross extravascular spaces
only class to cross placenta
many effector functions
Higher affinity than IgM
IgG1 and IgG3 are opsonins for phagocytic cells and can activate complement
IgA
Monomeric Igas in serum (some dimeric)
Dimeric igAs
most abundantly made antibody
monomers of IgA
Dimeric igAs
form are secreted on all MM, breast milk, sweat and tears
most abundantly made antibody
monomers of IgA
are joined by a j chain like the one used for joining IgM. also there is secretory component present on thos which are secreted this helps stabilize IgAs so they last longer on MM than other protiens
IgE
First exposure to Antigen (pollen or parasite ) causes IgE production
Mast cells (tissues),
eosinophil’s (MM)
basophils (blood)
all carry a receptor (Fc and R)this binds to Fc end of IgE even when not bound to antigen thus sensitization of these cells
during re-exposure to antigen which bridges the IgEs on these cells-> release of histamine and proinflammator mediatiors causing allergy or acts to fight parasite
basophils
blood
eosinophil
mm
mast cells
tissues
Change in immunoglobulin genes during a B cells life
1.V- region assembly from gene fragments
somatic recombination of genomic DNA this is irreversible
Change in immunoglobulin genes during a B cells life
2. generation of junctional diversity
imprecision in joining rearranged DNA segments adds nongermline nucleotides (P and N) and deletes gemline ducleotides
this is irreversible
Change in immunoglobulin genes during a B cells life
3. Assembly of transcriptional controlling elements
promoter and enhancer are brought closer together by V region assembly
Change in immunoglobulin genes during a B cells life
4.Transcription activated with coexpression of surface IgM and IgD
two patterns of splicing and processing RNA are used
reversible and regulated
Change in immunoglobulin genes during a B cells life
5. Synthesis changes from membrane Ig to secreted antibody
Two Patterns of splicing and processing RNA are used
reversible and regulated
Change in immunoglobulin genes during a B cells life
6. somatic hypermutation
point mutation of genomic DNA
Irreversible
Change in immunoglobulin genes during a B cells life
7. isotype switch
somatic recombination of genomic DNA
irreversible
