Download 3 pharmacy B cells

B CELLS
The simplest
Schema of the immune system
Innate immunity
Adaptive immunity
T cells
B cells
Recognition
Communication
Intracellular
pathogens
Elimination
Recognition
Extracellular
pathogens
Communication
Elimination
THE TWO ARMS OF THE IMMUNE SYSTEM
Monocytes, Macrophages,
Monocytes, Macrophages,
Dendritic cells, Granulocytes, NK
Dendritic cells, Granulocytes, NK
cells and Complement components
cells and Complement components
B and T cells
Overview of B cell–mediated immunity
B CELLS
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
B cell differentiation, memory cells, plasma cells
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
IMMUNOGLOBULINS
structure and function
STRUCTURE OF ANTIBODY
Heavy chain (H)
VH
VL
CH
Light chain (L)
CL
S
S
Symmetric core structure
2 identical heavy chain, 2 identical light chain
Variable regions  antigen binding
Constant regions
STRUCTURE
• heavy and light
chains
• disulfide bonds
– inter-chain
– intra-chain
disulfide
bond
carbohydrate
CL
VL
CH1
VH
CH2
hinge region
CH3
STRUCTURE
• variable and
constant regions
• hinge region
immunoglobulin domen
disulfide
bond
carbohydrate
• domains
– VL & CL
– VH & CH1 - CH3
(or CH4)
• oligosaccharides
CL
VL
CH1
VH
CH2
hinge region
CH3
ANTIBODY DOMAINS AND THEIR FUNCTIONS
Antigen recognition
antigénkötés
s
s
s
s
s
s
VH
s
s
CH1
s
s
s
s
Variable
domain
va riábilis
d om ének
s
s
VL
s
ss
ss
s
konsta ns dom ének CH2 s
effektor funkc iók
s
s
s
Constant domain
s
s
CL
CH3 ss
s
s
s
s
Effector functions
Two identical binding site
Heavy chain and light chain compose the antigen binding surface
THE ROLE OF THE HINGE REGION
RIBBON STRUCTURE OF IGG
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
B cell differentiation, memory cells, plasma cells
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
ANTIGEN BINDING
VH
VL
VH
VL
Variable domens responsible for antigen binding
DIFFERENT VARIABLE REGIONS  DIFFERENT
ANTIGEN-BINDING SITES  DIFFERENT SPECIFICITIES
HYPERVARIABLE REGION –
COMPLEMENTARY DETERMINING REGION (CDR)
3 CDR regions in a V domain
VH & VL domains 3+3 CDR
HYPERVARIABLE REGION –
COMPLEMENTARY DETERMINING
REGION (CDR)
COMPLEMENTARY DETERMINING REGION (CDR)
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
B cell differentiation, memory cells, plasma cells
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
DIVERSITY OF LYMPHOCYTES
1012 lymphocytes in our body ( B and T lymphocytes)
All lymphocytes have a different receptor
Cc. (minimum) 10 million various (107) B lymphocyte clones with
different antigen-recognizing receptors
Cc. (minimum) 10 – 1000 million various (107 - 9) T lymphocyte
clones with different antigen-recognizing receptors
Several antibodies are expressed on B cells, (arround 100.000) but
all of them with the same specificity
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES
CLONAL EXPANSION OF THE SPECIFIC B CELLS.
B cell
Antigen
receptor, BCR
A n ti g e n
Ag
Activation
Clonal expansion
A n ti g e n
A n ti g e n
A n ti g e n
Clonal antigen receptors are expressed exclusively on Tand B lymphfocyties.
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES
CLONAL EXPANSION AND DIFFERENTIATION OF
THE SEPCIFIC B CELLS.
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES
CLONAL EXPANSION AND DIFFERENTIATION OF
THE SEPCIFIC B CELLS.
LYMPHOID ORGANS
Primary lymphoid organs:
- Bone marrow
- Thymus
Secondary lymphoid organs:
- Spleen
- Lymphatic vessels
- Lymph nodes
- Adenoids and tonsils
- MALT (Mucosal Associated Lymphoid Tissue)
GALT (Gut Associated Lymphoid Tissue)
BALT (Bronchus Associated Lymphoid Tissue)
SALT (Skin Associated Lymphoid Tissue)
NALT (Nasal Associated Lymphoid Tissue)
LYMPHOCYTES REACTING WITH SELF ANTIGEN
DURING THEIR DEVELOPMENT IN THE PRIMARY
LYMPHOID ORGANS, BECOME INACTIVATED OR
DIE BY APOPTOSIS.
MACFARLANE BURNET (1956 - 1960)
CLON SELECTION HYPOTHESIS
Antibodies are natural products that appear on the
cell surface as receptors and selectively react with the
antigen.
Lymphocyte receptors are variable and carry
various antigen-recognizing receptors.
‘Non-self’ antigens/pathogens encounter
existing lymphocyte pool (repertoire).
the
Antigens select their matching receptors from the
available lymphocyte pool, induce clonal proliferation
of specific clones and these clones differentiate to
antibody secreting plasma cells.
The clonally distributed antigen-recognizing
receptors represent about ~107 – 109 distinct antigenic
specificities.
MACFARLANE BURNET (1956 - 1960)
CLON SELECTION HYPOTHESIS
-
Lymphocytes are monospecific cells
- Antigen engagemnt result in the activation of
lymphocytes
- Activated lymphocytes differentiate and
proliferate but keep their antigen specificity
- Lymphocytes reacting with self antigen during
their development in the primary lymphoid
organs, become inactivated or die by apoptosis.
1. BCR (cell surface antibody) recognize the antigen
2. Clonal proliferation of specific B cells
3. Differenciation of activated B cells to plasma cell (antibody production) or memory
cell
Ag
Activated B cells
Plasma cells
4. To distinguish self-nonself is with the selection and killing of self dangerous clones
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
TWO FORMS OF ANTIBODY
-cell surface (BCR)
-soluble (on the surface of plasma cells antibody is not expressed)
Cell surface and soluble antibodies recognize the same antigen
B cell: Antibody on the cell surface
(BCR) function: cell activation
Plasma cell: production of antibody
antibod y-mediated effector functions
BCR (B cell receptor)
Associated chains
for signaling
ANTIBODY
Transmembrane
domain
Cytoplasmic
domain
MEMBRANE BOUND!
Antigen recognition and B cell
activation
SOLUBLE (freely circulating)
Antigen recognition and effector
functions.
Produced by plasma cells
B CELL ACTIVATION
B cell
BCR oligomerization results in B cell activation,
proliferation and differentiation
!
Soluble antibody-mediated functions
ANTIGEN BINDING
VH
VL
VH
VL
Variable domens responsible for antigen binding
The variable domain can:
• detect antigen
• block the active sites of toxins or pathogen-associated
molecules
• block interactions between host and pathogenassociated molecules
immune complex
The conception of immune complex
Complement proteins
IMMUNCOMPLEX
complexe of (1)antigens-(2)antibodies (3)complement components complex
Complement proteins
The variable domain can:
• detect antigen
• Neutralization:
block the active sites of toxins or pathogen-associated
molecules
block interactions between host and pathogenassociated molecules
NEUTRALIZATION
Covering of the pathogen’s surface prevents
replication and growth
Crucial factors of
anti-viral response
1.
Type I. Interferons
2.
NK cells
3.
Cytotoxic T cells
4.
Neutralizing antibodies
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS:
1. Neutralization (variable domen)
Fc part:
2. Complement activation
Via opsonization:
3. Phagocytosis
4. ADCC (antibody dependent celular cytotoxicity)
5. (mast cell degranulation)
WHY DO ANTIBODIES NEED AN FC REGION?
Fc region can activate
• inflammatory and effector functions associated with
cells
• inflammatory and effector functions of complement
• the trafficking of antigens into the antigen processing
pathways
IMMUNOGLOBULIN FRAGMENTS:
STRUCTURE/FUNCTION RELATIONSHIPS
antigen
binding
Fc or constant
region
complement binding site
binding to Fc
receptors
placental
transfer
Pathogen recognition by innate immune system
1. Directly via PRR
2. Indirectly via opsonization
Receptors for opsonin recognition
!
FC RECEPTORS
RECOGNIZE THE CONSTANT (FC) PART OF ANTIBODIES
FC RECEPTORS
Expression of Fc receptors on the cell surface is constitutive (relativelly)
Fc receptors are not activated by free/lonely antibody but by
immunocomplexes
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS:
1. Neutralization (variable domen)
Fc part:
2. Complement activation
Via opsonization:
3. Phagocytosis
4. ADCC (antibody dependent celular cytotoxicity)
5. (mast cell degranulation)
COMPLEMENT ACTIVATION
GENERATES
INFLAMMATION
OPSONIZATION
KlLLING of
PATHOGEN
REMOVE
IMMUNKOPLEXES
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS:
1. Neutralization (variable domen)
Fc part:
2. Complement activation
Via opsonization:
3. Phagocytosis
4. ADCC (antibody dependent celular cytotoxicity)
5. (mast cell degranulation)
OPSONIZATION
Flagging a pathogen
Antigen binding portion (Fab)
binds the pathogen, the Fc region
binds phagocytic cells Fcreceptors speeding up the
process of phagocytosis
Opsonins:
ANTIBODY
Complement components
Acute phase proteins
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS:
1. Neutralization (variable domen)
Fc part:
2. Complement activation
Via opsonization:
3. Phagocytosis
4. ADCC (antibody dependent celular cytotoxicity)
5. (mast cell degranulation)
ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADCC)
DEGRANULATION OF NK CELLS
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS:
1. Neutralization (variable domen)
Fc part:
2. Complement activation
Via opsonization:
3. Phagocytosis
4. ADCC (antibody dependent celular cytotoxicity)
5. (mast cell degranulation)
INNATE IMMUNITY
Killing:
•Phagocytosis
•Soluble mediators
•Complement system
•NK cells
Antibody-mediated effector functions accelerates and
facitlitates the effector functions of innate immune system
B cell memory:
Quicker response
Increase in the number of specific B cell
The amount of antibody are higher
Higher affinity antibodies (‘more specific’)
Isotype switch
In case of T dependent B cell activation
During Memory response:
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
ANTIBODY DOMAINS AND THEIR FUNCTIONS
Antigen recognition
antigénkötés
s
s
s
s
s
s
VH
s
s
CH1
s
s
s
s
Variable
domain
va riábilis
d om ének
s
s
VL
s
ss
ss
s
konsta ns dom ének CH2 s
effektor funkc iók
Effector functions
CH3 ss
s
s
s
s
s
s
s
Constant domain
s
s
CL
HUMAN IMMUNOGLOBULIN CLASSES
encoded by different structural gene segments (isotypes)
•
•
•
•
•
IgG - gamma (γ) heavy chains
IgM - mu (μ) heavy chains
IgA - alpha (α) heavy chains
IgD - delta (δ) heavy chains
IgE - epsilon (ε) heavy chains
light chain types
• kappa (κ)
• lambda (λ)
FC RECEPTORS
Expression of Fc receptors on the cell surface is constitutive (relativelly)
Different cells express various Fc receptors
Antibodies with diferent izotype activates distinct cells, effector
functions
Fc receptors are not activated by free/lonely antibody but by
immunocomplexes
FcE receptor (for IgE) on mast cells initiate allergic rections
IZOTYPE SWITCH
MAIN CHARACTERISTICS OF ANTIBODY ISOTYPES
Ig isotype
Serum
concentration
Characteristics, functions
Trace
amounts
 Major isotype of secondary
(memory) immune response
 Complexed with antigen activates
effector functions (Fc-receptor
binding, complement activation
 The first isotype in B-lymphocyte
membrane
 Function in serum is not known
Trace
amounts
 Major isotype in protection against
parasites
 Mediator of allergic reactions (binds
to basophils and mast cells)
3-3,5 mg/ml
 Major isotype of secretions (saliva,
tear, milk)
 Protection of mucosal surfaces
12-14 mg/ml
1-2 mg/ml
 Major isotype of primary immune
responses
 Complexed with antigen activates
complement
 Agglutinates microbes
 The monomeric form is expressed in
B-lymphocyte membrane as antigen
binding receptor
free IgM pentamer (star shape)
Antigen bound IgM (crab shape)
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
The antigen presentation of B cells
is a BCR-dependent process!
ANTIGEN PRESENTATION OF B CELLS
B CELL-MEDIATED ANTIGEN PRESENTATION
1
B-sejt
MHCII
+ peptid
T-sejt
CD4
TCR
2
citokinek
+++
ANTIBODY-MEDIATED FUNCTIONS:
Cell surface (BCR):
- antigen recognition
- B cell activation
- (antigen presentation)
Soluble:
effekctor functions
1. Neutralization (variable domen)
Fc part:
2. complement activation
Via opsonization:
3. Phagocytosis
4. ADCC
IMMUNOGLOBULIN STRUCTURE-FUNCTION RELATIONSHIP
• cell surface antigen receptor on B cells (BCR)
allows B cells to sense their antigenic environment
connects extracellular space with intracellular signalling
machinery
• secreted antibody
neutralization
opsonization
complement fixation
NK cell –mediated killing
The simplest
Schema of the immune system
Innate immunity
Adaptive immunity
T cells
B cells
Recognition
Communication
Intracellular
pathogens
Elimination
Recognition
Extracellular
pathogens
Communication
Elimination