B CELLS. THE TWO ARMS OF THE IMMUNE SYSTEM Monocytes, Macrophages, Dendritic cells, Granulocytes, NK...
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Transcript of B CELLS. THE TWO ARMS OF THE IMMUNE SYSTEM Monocytes, Macrophages, Dendritic cells, Granulocytes, NK...
B CELLS
THE TWO ARMS OF THE IMMUNE SYSTEMTHE TWO ARMS OF THE IMMUNE SYSTEM
Monocytes, Macrophages, Dendritic cells, Granulocytes, NK
cells and Complement componentsB and T cells
Monocytes, Macrophages, Dendritic cells, Granulocytes, NK
cells and Complement components
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
IMMUNOGLOBULINSIMMUNOGLOBULINS
structure and function
STRUCTURE OF ANTIBODY STRUCTURE OF ANTIBODY
SS
Light chain (L)
Heavy chain (H)
VL
CL
VH
CH
Symmetric core structure 2 identical heavy chain, 2 identical light chain
Variable regions antigen bindingConstant regions
STRUCTURESTRUCTURE
• heavy and light chains
• disulfide bonds– inter-chain– intra-chain
hinge region
carbohydrate
disulfide bond
CH1
VL
CL
VH
CH2 CH3
• variable and constant regions
• hinge region
• domains– VL & CL
– VH & CH1 - CH3 (or CH4)
• oligosaccharides
hinge region
carbohydrate
disulfide bond
CH1
CL
VH
CH2 CH3
VL
immunoglobulin domen
STRUCTURESTRUCTURE
s
s
s
s
s
s
s
s
s ss s
CH2
CH3
s
s
s
s
s
s
s
s
ss
VL
VH
CL
CH1 ss
ss
ss
ss
ss
effektor funkciók
konstans domének
antigénkötés
variábilis domének
ANTIBODY DOMAINS AND THEIR FUNCTIONSANTIBODY DOMAINS AND THEIR FUNCTIONS
Constant domain
Effector functions
Antigen recognition
Variable domain
Two identical binding siteHeavy chain and light chain compose the antigen binding surface
THE ROLE OF THE HINGE REGIONTHE ROLE OF THE HINGE REGION
RIBBON STRUCTURE OF IGGRIBBON 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
VLVLVHVH
ANTIGEN BINDINGANTIGEN BINDING
Variable domens responsible for antigen binding
DIFFERENT VARIABLE REGIONS DIFFERENT VARIABLE REGIONS DIFFERENT DIFFERENT ANTIGEN-BINDING SITES ANTIGEN-BINDING SITES DIFFERENT SPECIFICITIES DIFFERENT SPECIFICITIES
3 CDR regions in a V domain
VH & VL domains 3+3 CDR
HYPERVARIABLE REGION –HYPERVARIABLE REGION – COMPLEMENTARY DETERMINING REGION (CDR)COMPLEMENTARY DETERMINING REGION (CDR)
HYPERVARIABLE REGION – HYPERVARIABLE REGION – COMPLEMENTARY DETERMINING COMPLEMENTARY DETERMINING
REGION (CDR)REGION (CDR)
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
Cc. (minimum) 10 mCc. (minimum) 10 milliillion various (10on various (1077) B lymphocyte clones with ) B lymphocyte clones with different different aantigntigeen-recognizing receptorsn-recognizing receptors
CCc. (minimum) 10 – 1000 mc. (minimum) 10 – 1000 milliillion various (10on various (1077 - - 99) ) TT lymphocyte lymphocyte clones with different clones with different aantigntigeen-recognizing receptorsn-recognizing receptors
DIVERSITY OF LYMPHOCYTESDIVERSITY OF LYMPHOCYTES
AAll lymphocytes have a different receptor ll lymphocytes have a different receptor
10101212 l lyymphocytes in our body ( B and T lymphocytesmphocytes in our body ( B and T lymphocytes))
Several antibodies are expressed on B cells, (arround 100.000) but all of them with the same specificity
Antigen
ActivationClonal expansion
B cell
Antigen receptor, BCR
Ag
Clonal antigen receptors are expressed exclusively on T- and B lymphfocyties.
Antigen
Antigen
Antigen
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES CLONAL EXPANSION OF THE SPECIFIC B CELLS.CLONAL EXPANSION OF THE SPECIFIC B CELLS.
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES CLONAL EXPANSION AND CLONAL EXPANSION AND DIFFERENTIATIONDIFFERENTIATION OF OF
THE SEPCIFIC B CELLS.THE SEPCIFIC B CELLS.
ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES ANTIGEN RECOGNITION BY SPECIFIC BCR INDUCES CLONAL EXPANSION AND DIFFERENTIATION OF CLONAL EXPANSION AND DIFFERENTIATION OF
THE SEPCIFIC B CELLS.THE SEPCIFIC B CELLS.
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)
LYMPHOID ORGANSLYMPHOID ORGANS
LYMPHOCYTES REACTING WITH SELF ANTIGEN LYMPHOCYTES REACTING WITH SELF ANTIGEN DURING THEIR DEVELOPMENT IN THE PRIMARY DURING THEIR DEVELOPMENT IN THE PRIMARY LYMPHOID ORGANS, BECOME INACTIVATED OR LYMPHOID ORGANS, BECOME INACTIVATED OR
DIE BY APOPTOSIS. DIE BY APOPTOSIS.
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 the existing lymphocyte pool (repertoire).
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)MACFARLANE BURNET (1956 - 1960) CCLLOON SELEN SELECTION HYPOTHESISCTION HYPOTHESIS
MACFARLANE BURNET (1956 - 1960)MACFARLANE BURNET (1956 - 1960) CCLLOON SELEN SELECTION HYPOTHESISCTION 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 cells3. Differenciation of activated B cells to plasma cell (antibody production) or memory
cell
4. To distinguish self-nonself is with the selection and killing of self dangerous clones
Activated B cells Plasma cells
Ag
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
B cell: Antibody on the cell surface (BCR) function: cell activation
Plasma cell: production of antibody antibod y-mediated effector functions
TWO FORMS OF ANTIBODYTWO 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
ANTIBODYANTIBODYBCR (BCR (B cell receptorB cell receptor))
MEMBRANE BOUND!
Associated chains for signaling
Transmembrane domain
Cytoplasmic domain
Antigen recognition and B cell activation
SOLUBLE (freely circulating)
Antigen recognition and effector functions.
Produced by plasma cells
B cell
B CELL ACTIVATIONB CELL ACTIVATION
BCR oligomerization results in B cell activation, proliferation and differentiation
!
VLVLVHVH
ANTIGEN BINDINGANTIGEN BINDING
Variable domens responsible for antigen binding
•detect antigen
•precipitate antigen
•block the active sites of toxins or pathogen-associated molecules
•block interactions between host and pathogen-associated molecules
The variable domain can:
•detect antigen
•precipitate antigen
•block the active sites of toxins or pathogen-associated molecules
•block interactions between host and pathogen-associated molecules
The variable domain can:
Complement proteins
•detect antigen
•precipitate antigen
•block the active sites of toxins or pathogen-associated molecules
•block interactions between host and pathogen-associated molecules
The variable domain can:
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS: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)
NEUTRALIZATIONNEUTRALIZATION
Covering of the pathogen’s surface prevents replication and growth
WHY DO ANTIBODIES NEED AN FC REGION?WHY DO ANTIBODIES NEED AN FC REGION?
•inflammatory and effector functions associated with cells
•inflammatory and effector functions of complement
•the trafficking of antigens into the antigen processing pathways
Fc region can activate
IMMUNOGLOBULIN FRAGMENTS: IMMUNOGLOBULIN FRAGMENTS: STRUCTURE/FUNCTION RELATIONSHIPSSTRUCTURE/FUNCTION RELATIONSHIPS
antigen binding
complement binding site
placental transfer
binding to Fc receptors
FC RECEPTORSFC RECEPTORSRECOGNIZE THE CONSTANT (FC) PART OF ANTIBODIESRECOGNIZE THE CONSTANT (FC) PART OF ANTIBODIES
!
Expression of Fc receptors on the cell surface is constitutive (relativelly)
Fc receptors are not activated by free/lonely antibody but by immunocomplexes
FC RECEPTORSFC RECEPTORS
FcR Affinity for Immunoglobulin Cell Distribution Function
FcγRI (CD64) High (Kd < 10-9 M); binds IgG1 and IgG3, can bind monomeric IgG
Macrophages, neutrophils; also eosinophils
Phagocytosis; activation of phagocytes
FcγRIIA (CD32) Low (Kd > 10-7 M) Macrophages, neutrophils; eosinophils, platelets
Phagocytosis; cell activation (inefficient)
FcγRIIB (CD32) Low (Kd > 10-7 M) B lymphocytes Feedback inhibition of B cells
FcγRIIC (CD32) Low (Kd > 10-7 M) Macrophages, neutrophils, NK cells
Phagocytosis, cell activation
FcγRIIIA (CD16) Low (Kd > 10-6 M) NK cells Antibody-dependent cell-mediated cytotoxicity
FcγRIIIB (CD16) Low (Kd > 10-6 M); GPI-linked protein
Neutrophils Phagocytosis (inefficient)
FcΕRI High (Kd > 10-10 M); binds monomeric IgE
Mast cells, basophils, eosinophils
Cell activation (degranulation)
FcΕRII (CD23) Low (Kd > 10-7 M) B lymphocytes, eosinophils, Langerhans cells
Unknown
FcαR (CD89) Low (Kd > 10-6 M) Neutrophils, eosinophils, monocytes
Cell activation?
Complement proteins
IMMUNCOMPLEX IMMUNCOMPLEX complexe of (1)antigens-(2)antibodies (3)complement components complex
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS: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 ACTIVATIONCOMPLEMENT ACTIVATION
GENERATES INFLAMMATION
OPSONIZATION
KlLLING of PATHOGEN
REMOVE IMMUNKOPLEXES
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS: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)
OPSONIZATIONOPSONIZATIONFlagging a pathogen
Antigen binding portion (Fab) binds the pathogen, the Fc region
binds phagocytic cells Fc-receptors speeding up the
process of phagocytosis
Opsonins:ANTIBODY
Complement componentsAcute phase proteins
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS: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)
DEGRANULATION OF NK CELLSDEGRANULATION OF NK CELLS
ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADCC)ANTIBODY DEPENDENT CELLULAR CYTOTOXICITY (ADCC)
ANTIBODY-MEDIATED EFFECTOR FUNCTIONS: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 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 cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
s
s
s
s
s
s
s
s
s ss s
CH2
CH3
s
s
s
s
s
s
s
s
ss
VL
VH
CL
CH1 ss
ss
ss
ss
ss
effektor funkciók
konstans domének
antigénkötés
variábilis domének
ANTIBODY DOMAINS AND THEIR FUNCTIONSANTIBODY DOMAINS AND THEIR FUNCTIONS
Constant domain
Effector functions
Antigen recognition
Variable domain
HUMAN IMMUNOGLOBULIN CLASSESHUMAN IMMUNOGLOBULIN CLASSESencoded 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)
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
FC RECEPTORSFC RECEPTORS
IZOTYPE SWITCHIZOTYPE SWITCH
Ig isotype Serum concentration
Characteristics, functions
12-14 mg/ml
Major isotype of secondary (memory) immune response
Complexed with antigen activates effector functions (Fc-receptor binding, complement activation
Trace
amounts
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
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
MAIN CHARACTERISTICS OF ANTIBODY ISOTYPESMAIN CHARACTERISTICS OF ANTIBODY ISOTYPES
free IgM pentamer (star shape)
Antigen bound IgM (crab shape)
valence
2
2
2
2-4-6
2-8-10-12
FcR Affinity for Immunoglobulin Cell Distribution Function
FcγRI (CD64) High (Kd < 10-9 M); binds IgG1 and IgG3, can bind monomeric IgG
Macrophages, neutrophils; also eosinophils
Phagocytosis; activation of phagocytes
FcγRIIA (CD32) Low (Kd > 10-7 M) Macrophages, neutrophils; eosinophils, platelets
Phagocytosis; cell activation (inefficient)
FcγRIIB (CD32) Low (Kd > 10-7 M) B lymphocytes Feedback inhibition of B cells
FcγRIIC (CD32) Low (Kd > 10-7 M) Macrophages, neutrophils, NK cells
Phagocytosis, cell activation
FcγRIIIA (CD16) Low (Kd > 10-6 M) NK cells Antibody-dependent cell-mediated cytotoxicity
FcγRIIIB (CD16) Low (Kd > 10-6 M); GPI-linked protein
Neutrophils Phagocytosis (inefficient)
FcΕRI High (Kd > 10-10 M); binds monomeric IgE
Mast cells, basophils, eosinophils
Cell activation (degranulation)
FcΕRII (CD23) Low (Kd > 10-7 M) B lymphocytes, eosinophils, Langerhans cells
Unknown
FcαR (CD89) Low (Kd > 10-6 M) Neutrophils, eosinophils, monocytes
Cell activation?
(Classes/subclasses)
Sequence variability of H/L-chain constant regions
Sequence variability of H and L-chain variable regions (individual, clone- specific)
Allelic variants
VARIABILITY IN DIFFERENT REGIONS OF THE IG VARIABILITY IN DIFFERENT REGIONS OF THE IG DETERMINES IG CLASSES OR SPECIFICITYDETERMINES IG CLASSES OR SPECIFICITY
isotype idiotypeallotype
B cells
Structure of antibody
Antigen binding/hypervariable regions
Clonal proliferation
Antibody-mediated effector functions
Izotypes
B cell mediated antigen presentation
ANTIGEN PRESENTATION OF B CELLSANTIGEN PRESENTATION OF B CELLS
B-se jt
c itokinek
C D4TC R
MHC II+ p ep tid
T-se jt
2
1
+++
B CELL-MEDIATED ANTIGEN PRESENTATIONB CELL-MEDIATED ANTIGEN PRESENTATION
•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
IMMUNOGLOBULIN STRUCTURE-FUNCTION RELATIONSHIPIMMUNOGLOBULIN STRUCTURE-FUNCTION RELATIONSHIP
ANTIBODY-MEDIATED FUNCTIONS:ANTIBODY-MEDIATED FUNCTIONS:
Cell surface (BCR):-antigen recognition-B cell activation-(antigen presentation)
Soluble:effekctor functions1. Neutralization (variable domen)
Fc part:
2. complement activation
Via opsonization:
3. Phagocytosis
4. ADCC