Download MHC gp I

HLA system
(MHC glycoproteins)
MHC glycoproteins class I
(Major histocompatibility complex)
 The function of MHCgpI is presentation of peptide
fragments from inside the cell (which are produced by
cell, including viral peptides if are present)on the cell
surface so as to be recognized by T lymphocytes
(cytotoxic, CD8)
 Present on all nucleated cells of the organism
 3 isotypes classical human MHC gp. (HLA - A,-B,-C)
 3 isotypes non-classical MHC gp. (HLA - E,-F,-G; molecule
CD1)
Antigen presentation to cytotoxic T cells
MHC gp I structure
 MHC gp class I consists of transmembrane
chain a and non-covalently associated
b2mikroglobulin
 a chain has 3 domains, 2 N-terminal (a1, a2 - binding
site for peptides) and 1 C-terminal domain (a3 anchored in the cytoplasmic membrane, a structure
similar to imunoglobulin domain)
MHC gpI peptide binding
 MHC gp I bind peptides with a length of 8 to 10
aminoacides
 Certain MHC gp molecule binds peptides sharing
common structural features - coupling motif (critical are
aminoacides near the end of peptide)
 The binding of endogenous peptides occurs in the
endoplasmic reticulum during biosynthesis of MHC gp I
 After a chain a and b2mikroglobulin create in the ER,
folding into the correct conformation and the mutual
association and the association of an appropriate
peptide, the complex is further processed in the Golgi
apparatus and then is presented on the cell surface
 Linked peptides are derived from proteins degraded by
proteasome, proteasom degradate unneeded or
damaged cytoplasmic proteins (labeled with ubiquitin),
peptide fragments are transported into the ER by specific
membrane pump TAP (transporter associated with
antigen processing
MHC gpI peptide binding
Binding the peptide to MHCgpI
Non-classical MHC gp I
 HLA - E,-F,-G; CD1 molecules
 Structurally similar to classical MHC gp
 Are less polymorphic
 There are only on some cells
 They specialize in binding of specific ligands
 HLA-E and HLA-G - occurs on the trophoblast cells
 Complexes of HLA-E and HLA-G with peptides are
recognized by inhibiting receptors of NK cells and
contribute to the tolerance of the fetus in utero
MHC glycoproteins class II
 The function of MHC gpII is the presentation of peptide
fragments from protein whitch are ingested by cell on
the cell surface so as to be recognized by T lymphocytes
(helper, CD4)
 Occur on the APC (dendritic cells, monocytes,
macrophages, B lymphocytes)
 3 isotypes of MHC gpII (DR, DQ, DP)
MHC gp II structure
 MHC gp II consist of 2 non-covalently associated
transmembrane subunits a and b
 The peptide binding site consists of N-terminal
domains a1 and b1
 Binding of peptide is necessary for a stable MHC gp
conformation and thus ensure its long presentation on
the cell surface
MHC gp II peptide binding
 MHC gpII bind peptides with a length of 15 to 35
aminoacides (but possibly longer - because the peptide
binding site is open at both ends)
 Certain MHC gp molecule binds peptides sharing
common structural features - coupling motif
 After a string a and b are created in ER, fold into the
correct conformation and the mutual associated are
connected with another transmembrane chain called
invariant chain, which blocks the binding site for the
peptide, this complex is further processed in the Golgi
apparatus, secretory vesicles isolated from GA merge
with endosomes, then split the invariant chain and
peptide fragments from cell absorbed proteins bind into
binding site of MHC gp and the complex is then
presented on cell surface

MHC gp II peptide binding
Antigen prezentation
Antigen presentation to T lymphocyte
1. Signal: TCR – MHC gp I(II)+Ag peptid (APC)
2. Co-stimulating signal: CD 28 (T lymphocyte) – CD 80, CD 86 (APC)
MHC glycoproteins polymorphism
 HLA complex is located on chromosome 6
 For MHC gp is typical high polymorphism, there are up to hundreds
of different forms of alelic isotypes (except the non-classical MHC
gp, and DR a chain)
 Codominant inheritance of alelic forms (Individual
has 3 cell surface isotypes of HLA molecules
(HLA-A,-B,-C) mostly in 2 different alelic forms)
 Polymorphism has a protective significance at individual and
population level
 MHC gp polymorphism causes complications in transplantation
HLA typing = determmination of HLA
antigens on the surface of lymphocytes
Carry out during the testing before transplantation and in
determination of paternity
 1) Serotyping
 Microlymfocytotoxic test
 Allospecific serums (obtained from multiple natal to 6 weeks after
birth, obtained by vaccination of volunteers, or commercially
prepared sets of typing serums (monoclonal antibodies))
 Principle - the incubation of lymphocytes with typing serums in the
presence of rabbit complement, then is added the vital
dye which stained dead cells
- cells carrying specific HLA are killed by cytotoxic Ab
against the Ag, the percentage of dead cells is a measure
of serum toxicity (forces and antileukocyte antibody titre)
 Positive reaction is considered more than 10% dead cells
(serological typing can be done also by flow cytometry
2) Molecular genetic methods
 For typing are used hypervariable sections in the II. exon
genes coding for HLA class II; to determine HLA class I is
used polymorphism in II. and III. exon coding genes
2a) PCR-SSP
= Polymerase chain reaction with sequential specific primers
 Extracted DNA is used as a substrate in a set of PCR reactions
 Each PCR reaction contains primers pair specific for a certain
allele (or group of alleles)
 Positive and negative reactions are evaluated by
electrophoresis, each combination of alleles has a specific
electrophoretic painting
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2b) PCR-SSO
PCR reaction with sequence-specific oligonucleotides
Multiplication of hypervariable sections of genes coding
HLA
Hybridization with enzyme or radiolabeled DNA probes
specific for individual alleles
2c) PCR-SBT
Sequencing based typing
The most accurate method of HLA typing
We get the exact sequence of nucleotides, which
compares with a database of known sequences of HLA
alleles
T – lymphocytes
J. Ochotná
T lymphocytes
 cellular component of antigen-specific mechanisms
 several different subsets of T lymphocytes
 regulation of immune processes, the destruction of virusinfected cells or tumor cells
 recognize antigen processed and presented by the APC
 T cells are after activation stimulated to multiplication
and differentiation into effector cells and part of them
differentiate into the memory cells
T-lymphocytes development

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T cells originate in bone marrow and then migrate to the thymus where
they mature (abT lymphocytes), the final differentiation is after activation
by antigen processed and presented by APC
gdT cells can develop outside the thymus (the minority population)
Pluripotent hematopoietic stem cells
Pro-thymocytes – double negative T cells - are coming from the bone
marrow to the thymus, where they begin to rearrange TCRb genes,
expressing on their surface, called pre-TCR (Composed of b chain, pre-TCRa
and CD3 complex), then begin TCRa genes rearrangement
Cortical thymocytes – double positive T cells - express on their surface
TCR (composed of chains a, b and CD3) and CD4 and CD8 co-receptor
(double positive T lymphocyte), at this stage occurs the selection of
autoreactive cells and cells with dysfunctional TCR
Medullary thymocytes (mature T cell) - retain the expression of CD4 or
CD8, then migrate to secondary lymphoid organs
T-lymphocytes selection
 Negative selection - the elimination of autoreactive cells, when
thymocytes binds enough strongly by their TCR complex of MHCgp
with normal peptides (from autoantigens)which are presented on
surface of thymic cells thymocyte receives signals leading to apoptotic
cell death
PAE cells (peripherial antigen expressing cells)
 Positive selection - the elimination of cells with dysfunctional TCR,
positively are selected thymocytes that recognize MHC gp with low
affinity, then maintain the expression of CD4 or CD8 (depending what
class of MHC gp binds to the TCR). These mature T cells (Medullary
thymocytes) leave the thymus and migrate to secondary lymphoid
organs
98% of pro-thymocytes in the thymus during its development dies
T cell development
T-lymphocytes surface markers
 TCR - recognizes Ag peptide complexed with MHC gp
 CD3 - TCR component, participation in signal transduction
 CD4 or CD8 - co-receptors, binding to MHC gp
 CD28 - costimulatory receptor, binds to CD80, CD86 on APC
 CTLA-4 (CD152) - inhibitory receptor, binds to CD80, CD86
Interaction between APC and T cell
T-lymphocytes subpopulations
 ab-T lymphocytes - have TCRab, major type
(95%), thymus need in development, recognize
antigens in the complex MHC-peptide gp
 gd-T lymphocytes - (5%) may develop outside
the thymus, some are able to recognize native
Ag, apply in defense of the skin and mucous
membranes
ab T-lymphocytes
Expressing the CD4 co-receptor (co-receptor for MHC
class II gp), precursors of helper T cells (TH), they can
be classified according to the production of cytokines
TH0 - produce a mixture of cytokines such as TH1 and TH2
TH1 - IL-2, IFNg (help macrophages )
TH2 - IL-4, IL-5, IL-6, IL-10 (B lymphocytes assistance)
TH3 - TGFb
Treg - regulatory T cells arise in the thymus from a part
of autoreactive lymphocytes, suppress the activity of TH1
and partly function as TS, suppression of autoreactive
T cell clones
ab T-lymphocytes
Expressing the CD8 co-receptor (co-receptor for MHC
gp class I), precursors of cytotoxic T cells (TC), or
suppressor T cells (TS)
TC - recognize cells infected by viruses or other
intracellular parasites and some cancer cells
TS - inhibit the function of other lymphocytes
TCR
 TCR (T cell receptor) is heterodimer
consisting of a and b (g,d) chain
and associated CD3 complex,
which is necessary for signal
transfer (is connected with PTK)
 "N-terminal parts of a and b (g,d) chain form the binding
site for Ag
TCR cooperation with co-receptors CD4, CD8
TCR development
 The analogy with the formation of BCR
 Chains b and d - correspond to IgH gene complex of
immunoglobulins
- V, D, J, C segments
 Chains a and g - correspond to genes for L chains of
immunoglobulins
- V, J, C segments
 Rearrangement of genes is similar to the BCR and
performed by the same recombinases
Antigen-specific mechanisms
TH1 based immune response
TH1 immune response
- inflammatory reaction
 TH1 cells cooperate with macrophages and transform them in
activated (NO production - destroy intracellular parasites)
 Activated macrophages secrete some cytokines (IL-1, TNF, ...)
that help to stimulate T cells and stimulate local inflammation,
which helps suppress infection
 Interaction between TH1 cells and macrophages is a
fundamental mechanism of delayed-type immunopathological
reactions (DTH Delayed-type hypersensitivity)
 The infected macrophage produces protein fragments
derived from intracellular parasites, some of which are
presented on the surface by MHC gp class II
 Macrophages and dendritic cells stimulated by certain
microorganisms produce IL-12
 TH precursor, which detects the infected macrophage and
receives signals via the TCR, CD 28 and receptor for IL-12
and other adhesion and signaling molecules proliferates
and differentiates to the effector TH1 cells that produce
IFNg and IL-2.
 IFNg activates macrophage NO synthase
IL-2 is an autocrine growth factor for TH1 cells
Interaction between APC and TH precursor
TH2 based immune response
TH2 immune response – help to B-lymphocytes
 TH2 cells cooperate with B lymphocytes (which were
stimulated by Ag) by cytokine production (IL-4, IL-5,
IL-6) and direct intercellular contact
 For stimulation of B lymphocytes is usually necessary
cooperation between APC → TH2 cell → B lymphocyte
 In minimal model, where the B cell becomes a good APC
(CD80, CD86) is sufficient cooperation between TH2 cell
→ B lymphocyte
 TH precursor, which detects the infected macrophage and
receives signals through the TCR, CD 28 receptor for IL-4
receptor and IL-2 and other adhesion and signaling
molecules proliferates and differentiates in the effector
TH2, which provide B lymphocytes auxiliary signals via
cytokines secreted by IL-4, IL-5, IL-6 and adhesion
molecules through CD 40L, which bind to the
costimulatory receptor on B lymphocytes CD 40
 Interaction between CD40 (B lymphocytes) and CD40L
(TH2 cells) is essential for the initiation of somatic
mutations, izotype switching and formation of memory
cells
 IL-4, IL-5, IL-6: stimulation of B lymphocytes
Assistance to B lymphocytes
Specific direct assistance to B lymphocytes:
 TH2 lymphocytes assisting B lymphocytes that were
stimulated by the same Ag, which caused the rise of TH2
 To stimulate the secretion of cytokines by TH2 cell is
sufficient signal via the TCR (signal through a
costimulatory receptor CD28 is no longer necessary)
 One clone of TH2 cells can provide specific assistance to
B lymphocytes of different specificities (must present the
relevant Ag peptides by MHC gp II, which are recognized
by TCR)
Assistance to B lymphocytes
Indirect assistance to B cells ("bystander help"):
 TH2 lymphocytes assisting B lymphocytes that were
stimulated by another Ag than that which caused the
rise of TH2
 Contact between TH2 cell → B lymphocytes via adhesion
molecules, cytokine secretion, binding CD40-CD40L
 Danger of activation autoreactive B lymphocytes
Mutual regulation of activities TH1versus TH2
 Whether the TH precursor cell will develop into TH1 or TH2 decides
cytokine ratio of IL-12 and IL-4
 IL-12 is produced by macrophages and dendritic cells stimulated by
certain microorganisms
 IL-4 is produced by activated basophils and mast cells
 TH1 cytokines (mainly IFNg) inhibit the development of TH2 and
stimulate the development of TH1 (IL-2 stimulates also TH2)
 Cytokines produced by TH2 (IL-4, IL-10) inhibit the development of
TH1 and stimulate the development of TH2
 TH3 development is stimulated by a specific cytokine environment
(IL-4, IL-10, TGFb); TH3 produce TGFb and cooperate with B cells in
MALT
TC based immune response
Cytotoxic T lymphocytes stimulation
 TC recognize cells infected with viruses or other
intracellular parasites, and some tumor cells
 Precursor of TC, which recognizes a complex
of MHC gp I- antigenic peptide on the surface of APC via
TCR and receives signals via CD 28 proliferates and
differentiates to clone mature effector cytotoxic cells
(CTL); TH1 cells help to TC by production IL-2
 Effector TC are spread by bloodstream into tissues; for
activation of cytotoxic mechanisms is sufficient signal
through the TCR (signal through a costimulatory
receptor CD28 is no longer necessary)
 Professional APC are dendritic cells or macrophages that
are infected with virus, or swallowed antigens from dead
infected, tumor or stressed cells
 In order APC could activate the TC precursor, APC must
be stimulated by contact with TH cells via CD 40, then
the dendritic cell begins to express CD 80, CD86 and
secrete cytokines (IL-1, IL-12) = change of resting APC
in activated
Tc effector functions
 Cytotoxic granules containing perforin and granzymes
(perforin creates pores in the cytoplasmic membrane of
target cell, in some cases may lead to osmotic lysis of
the target cell, formed pores in the cell receiving
granzymes that cause the target cell to die by
apoptosis.
 Fas ligand (FasL) - which binds to the apoptotic
receptor Fas (CD95) presented on the surface of many
different cells (also on the surface of TC)
 TNFb
Antibody-based immune
response
Antibody responses induced by
 T-independent antigens
 Cause predominantly IgM production
 Bacterial polysaccharides, lipopolysaccharides, and
polymeric forms of protein
 T-dependent antigens
 Reaction to these Ag occurs in two phases primary and secondary response
 Initiate the development of memory cells and
formation of high-affinity antibodies
T-independent and
T-dependent immune
response
Antibody responses induced
by T-dependent antigen
Primary phase of antibody response
 The first contact with Ag
 Takes place in secondary lymphoid organs
 Stimulation of B cells by Ag binding to BCR
 Ag absorption by APC and its presentation via MHC gp class II
to precursors of TH cell → formation of clone of antigenspecific TH2 cells, which provide assistance to competent B
lymphocytes, leading to their proliferation, differentiation into
plasma (produce Ab) and memory cells
 Plasma cells are spread by bloodstream into the
organism (particularly bone marrow)
 Antibodies produced in the primary stage (3-4 days) are
IgM and have a low affinity for Ag, create with Ag
immune complexes
 Immune complexes are captured in the secondary
lymphoid organs on the surface of FDC (follicular
dendritic cells) - Ag presenting cells to B lymphocytes
Secondary phase of antibodies response
 Recognition of Ag on FDC
(If is sufficient amount of immune complexes on FDCs)
 Under the influence of signals from the FDC (Ag) and
TH2 cells (CD40L, cytokines) is again started the
proliferation and differentiation of B cells accompanied
with somatic mutations → formation of clones of B cells
with new BCR → survive only B cells with a BCR with the
highest affinity for Ag = affinity maturation of antibodies
 There is also isotype switching, which isotypes arise
determines cytokine environment
 In the secondary phase of the immune response
generate antibodies with higher affinity for Ag and other
effector characteristics dependent on isotype, also
formed a memory cells for next meeting with the Ag
 Antibodies in the body after primary infection persist for
a long time
 Contact between CD40 (B lymphocytes) and CD40L (TH2
lymphocytes) is essential for the initiation of somatic
mutations, isotype switching and formation of memory
cells
Primary and secondary immune reaction
• Primary immune reaction – occurs on the firsth
exposure to antigen
• Secondary immune reaction –occurs after
subsequent encounter with the same antigen and is
more rapid leading to the activation of previously
generated memory cells
Primary and secondary immune reaction
B lymphocytes
B-lymphocytes
 B-lymphocytes (B cells) are cells responsible
especially for specific, antibody-mediated immune
response. They also have great importance for the
immune memory (which is used for vaccination).
 B-cells recognize native antigen through BCR (B cell
receptor)
 B-lymphocyte whitch bind Ag through BCR are
stimulated to proliferate and differentiate to effector
plasma cells which produce large quantities of antibodies
of the same specificity as the BCR (it is actually the
same protein in soluble form). Part of stimulated B-cells
differentiate to memory cells.
Surface characteristics of B lymphocytes
 CD 10 - immature B lymphocyte
 CD 19 - characteristic surface sign of B cells
 CD 20 - on the surface of Ig-positive B lymphocytes
 IgM, IgD - BCR
 MHC gp II - Ag presenting molecules
 CD 40 – costimulating receptor
B cell development
 Development of B lymphocytes takes place in the bone marrow and
completes after activation with Ag in secondary lymphoid organs.
Pluripotent hematopoietic stem cell
Progenitor B cell - begin recombination processes which lead
to a large number of clones B lymphocytes
with individual specific BCR
Pre - B cell - expression of pre-B receptor (composed of H (m)
chain and alternate L chain)
Immature - B lymphocyte - expression of surface IgM (BCR)
at this stage elimination
of autoreactive clones
Mature B lymphocyte - expression of surface IgM and IgD (BCR)
Critical moments in the B cell
development
 Completion of the rearrangment of genes for H chain
and surface expression of pre-BCR
 Successful rearrangement of genes for L chain and
surface expression of IgM (BCR)
 Testing of immature B cells, whether they are
autoreactive
 Another critical stage are somatic mutations and affinity
maturation, when survive only B cells with the highest
affinity for antigen.
BCR
 BCR is composed from surface
immunoglobulin (IgM, IgD - H chains are
transmembrane, recognizes Ag) and
associated signaling molecules (Iga and
IGb), which are associated with the
cytoplasmic protein-tyrosine kinases (PTK)
Src Group
 After binding of Ag to 2 or more BCR will
approximate PTK, mutual phosphorylation
and phosphorylation of other cytoplasmic
proteins, leading to changes in gene
transcription, proliferation, differentiation and
secretion of antibodies
 The signal by binding Ag to the BCR can be
amplified by cooperation with CR2, which
binds C3dg (opsonin)
Elimination of autoreactive B lymphocytes
 By random rearrangement of genes, connecting inaccuracy, H-L
pairing and somatic mutations may also arise clones of B cells
bearing autoreactive receptors and produce autoreactive antibodies.
 Majority of autoreactive B lymphocytes are eliminated as the
immature B lymphocytes in the bone marrow, if its BCR bind
autoantigen with sufficient affinity, receives a signal leading to
apoptotic death (clonal deletion).
 If some of the autoreactive clones pass this elimination, their
autoreaktivity usually do not come because lack of TH lymphocytes
for their activation, many autoantigens are cryptic, or occur in low
concentrations and are ignored by the immune system.
Tolerance to self-antigens is critical in preventing autoimmunity in
the organism.
Antigen recognition by B cell
in secondary lymphoid organs
Ontogenesis of antibodies
 Synthesis of specific antibodies begins around the 20.-24.
week of gestation, the total concentration of IgA and IgM
remains undetectable until birth, IgG begin to form after
birth
 B lymphocytes respond to immunization predominantly by
IgM formation, switching to other isotype is slower
 Slow growth of own IgG decline in maternal IgG (about 3.
to 6.month)
 The IgM concentration reaches values
comparable
to adults in the 1- 3 year of life, IgG and IgA
between 10.-15. year
 Antibody response to polysaccharide antigens
appears until around 2. year of life
 In old age is a lower antibody response to new
stimuli and increased autoantibodies production
Immunoglobulins
Immunoglobulin structure
 2 heavy (H) chains covalently linked by disulfide bonds,
each H chain is connected to a light (L) chain by
disulfide bonds
 H chain consists of 4 to 5 domains (1 variable, 3-4
constant)
 L chain consists of 2 immunoglobulin domains
(1 variable, 1 constant)
 Types of L chains - k, l
 Types of H chains - m, d, g (g1-4) and (a1, a2), e
 Variable domains of L and H chain form the binding site
for Ag
 Hinge region where the heavy chain linked by disulfide
bonds
 Immunoglobulins are glykoproteins (glycosilated Fc part)
 J chain
 Secretory component
Immunoglobulins functions
 Antigen neutralization
 Antigen agglutination
 Complement activation (IgM, IgG)
 Opsonization (IgA, IgG, IgE)
 Mast cell activation using IgE
 ADCC
Classes of immunoglobulins and their
functions
 Distinguished by the constant part of H chain to
IgM, IgD, IgG (IgG1 - IgG4), IgA (IgA1, IgA2), IgE
 IgM - as a monomer form BCR
- secreted as pentamer (10 binding sites)
- first isotype that forms after the meeting with Ag
- neutralization of Ag, activates complement,
do not bind to Fc receptors on phagocytes
- (concentration of 0.9 to 2.5 g / l; biol. half-life
6 days)
 IgD - monomer form a BCR
- in serum is in a very low concentration
- (0.1 g / l; biol. half-life 3 days)
 IgG - isotypes IgG1-IgG4 different ability of complement
activation and binding to Fc receptors of
phagocytes (opsonization)
- function: neutralization, opsonization, complement
activation
- passes the placenta (passive imunization from the
mother)
- formed in secondary immune response
- (concentration of 8 to 18 g / l; biol. half-life of 21
days)
 IgA - mucosal IgA - protection of mucous membranes,
neutralization, opsonization,
do not activate complement
- dimer, the secretory component
- saliva, tears, breast milk
- serum IgA - monomer, dimer or trimer
- (Concentration of 0.9 to 3.5 g / l;
biol. half-life of 6 days)
 IgE - applies in defense against multicellular parasites
- is the main cause of allergic reactions
- (concentration of 3x10-4 g / l; biol. half-life 2 days)
The genetic basis for the development of
immunoglobulin
The genetic basis of the immunoglobulins
development
 Gene segments for H chains – on chromosome 14
V (variable)
D (Diversity)
J (joining)
C constant domains of H chain
 Gene segments for L chains - k on chromosome 2
- l on chromosome 22
V (variable)
J (joining)
C constant domain of L chain
 At the ends of V, D, J segments that are signal sequences which are
recognized enzyme VDJ recombinase that carry out the
rearrangement of these genes
 On the sides of C segments are so-called switch sequences, which
are recognized by enzyme recombinase that carry out isotype
switching
The rearrangement of genes coding H chain
1) DJ rearrangement - excision a section IgH between
D and J segment (runs on both chromosomes)
2) VD rearrangement - excision section between some
V segment and DJ, if is rearrangement on some
chromosome successfull, stops the regrouping on the
second chromosome – it is called allelic exclusion (this is
also true for L chain)
Transcript of rearranged IgH gene into mRNA , splicing
of the primary transcript. The first form H chain m.
If rearrangement is unsuccessful, B lymphocyte die.
The rearrangement of genes coding L chain
1) First, rearrange the genes encoding the L chain k,
there is excision of sections between a V and J segment
(simultaneously on both chromosomes), if the
rearrangement is successful on one chromosomes,
regrouping on the second chromosome stops – it is
called allelic exclusion.
2) If regrouping of the k genes is unsuccessful, start the
regrouping genes l.
3) Not all H and L chain can form together a stable
dimmers.
If regrouping unsuccessful, B lymphocyte die.
Isotype (class) switching
 Occurs during the terminal differentiation of B lymphocyte
after activation with Ag on the surface of FDC (require
costimulating signal through CD40)
 Enzymes recombinases recognize the switch sequences
located on the sides of C segments (this sequence is not
between Cm and Cd segments - B cell can produce before
isotype class switching IgM and IgD simultaneously) and
excise gene segments
 After elimination of the C domain part is transcribed into
mRNA that segment, which is the closest to VDJ segment
and after splicing and translation arise corresponding
isotype of the H chain
Isotype switching
Isotype switching
 Cytokines regulate which isotype occurs:
IL-4 stimulates switching to IgE and IgG1, IgG4
TGFb stimulates switching to IgG2 and IgA
Anti-idiotypic antibodies
 IDIOTYP = summary of identical
binding structures for Ag on
antibodies the same specificity
 Idiotypic structures of 1st generation antibodies can be
recognized by some B lymphocytes as antigens and can
form against them anti-idiotypic antibodies (2nd
generation antibodies; some binding sites may remind
Ag, which caused formation of 1st generation
antibodies)
 Against the 2nd generation antibodies formate 3rd
generation antibodies (anti-antiidiotypic antibodies)
 The idiotypic network may play a role in regulation of
antibody response