2nd seminar: THE ANTIGEN Definition and properties Antigenic determinant (epitope) Hapten, carrier...
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Transcript of 2nd seminar: THE ANTIGEN Definition and properties Antigenic determinant (epitope) Hapten, carrier...
2nd seminar:2nd seminar:THE ANTIGENTHE ANTIGEN
Definition and properties
Antigenic determinant (epitope)
Hapten, carrier
Antigen recognition by B and T cells
Superantigens
ACUTE ACUTE INFLAMMATIONINFLAMMATION
Any chemical structure
Soluble or corpuscle
Simple or complex
Originated from the body or comes from outside
Genetically self or non-self
Natural or artificial
• ANTIGEN (Ag) - any substance, which is recognized by the mature immune system of a given organism
DEFINITIONSDEFINITIONS
• ANTIGENICITY– capability of an antigen to bind to bind specificallyspecifically with certain product of the adaptive immunity: TCR or BCR/antibody,
– immunogenicity - capability of an antigen to induceinduce an (adaptive) immune response,
– tolerogenicity - capability to induce immunological tolerance, specific immune non-responsiveness
DEFINITIONSDEFINITIONS
FACTORS INFLUENCING FACTORS INFLUENCING IMMUNOGENICITY I.IMMUNOGENICITY I.
From the aspect of our body:
• Genetics (self/non-self)– species (evolutionarily nonconserved molecules)– individual differences (e.g. MHC polymorphism – see later)
• Age – newborn – less reactive immune system– elderly – no new lymphocytes
• Physiological condition (pl. immunodeficiencies, starvation)
FACTORS INFLUENCING FACTORS INFLUENCING IMMUNOGENICITY II.IMMUNOGENICITY II.
From the aspect of the antigen:
• Physical-chemical properties of the Ag
– size/complexity (bigger more epitopes, role of carrier)– corpuscular (cell, colloid) or soluble– denatured or native (different epitopes!)– degradability (by APCs)
• Availability (crystalline proteins of the eye are not presented to lymphocytes)
FACTORS INFLUENCING FACTORS INFLUENCING IMMUNOGENICITY IIIMMUNOGENICITY IIII..
From the aspect of vaccination:
• Dose• Route
– intradermal/subcutan > intravenous > oral > intranasal (oral vaccine against polio virus!)
• Adjuvant– enhance the response given to the antigen
e.g.: alum, Freund-adjuvant, TLR ligands
Complex effects:• depot effect long-lasting presence of antigen• activation of innate immunity• activation of bystander cells
T B
BCR(membrane Ig)
antibodies (serum Ig)
TCR
APC
MHC
B cells recognise native antigensT cells recognise processed antigens
Antigen
ANTIGEN RECOGNITION BY LYMPHOCYTES
Part of the antigen which directly interacts with the antigen-binding site of a defined immunoglobulin (BCR / antibody) or TCR
ANTIGENIC DETERMINANT (ANTIGENIC DETERMINANT (==EPITOPE)EPITOPE)
B cell epitopeB cell epitope T cell epitopeT cell epitope
recognized by B cells
• proteins polysaccharides lipids DNA steroids etc. (many artificial molecules)
• cell or matrix associated or soluble
recognized by T cells
• proteins mainly (8-23 amino acids)
• requires processing by APC
Antigens may have several different epitopesAntigens may have several different epitopes
Epitopes
Theoretical structure of complex antigens
„Carrier”no direct interaction with the antigen-binding site
These terms can only be used to describe the interaction of particular antigenic determinant and single immunoglobulin or T cell receptor
Antibody 1
Antibody 2Epitope 1
„carrier” (1)
Epitope 2
„carrier” (2)
Antigén
EPITOPE AND „CARRIER”
Ab1Ab2
hidden/revealed determinant
denaturation
new/neoantigen determinant
conformational determinant
cleveage
conformational/linear determinant
TYPES (STRUCTURE) OF ANTIGEN DETERMINANTSTYPES (STRUCTURE) OF ANTIGEN DETERMINANTS
surface/accessible determinants
linear determinantlinear determinant conformational determinantconformational determinant
(TCR, BCR, Ig) (BCR, Ig)
LPS – antigen or PAMP?!
Antigenif recognised by TCR/BCR
PAMPif recognized by PRR (TLR4)
LPS
Fc
specific antibody reactive to the glucoseamin epitope of LPS
Fab
Fab
side view
top view
ANTIGEN RECOGNITION ≠ CELL ACTIVATIONANTIGEN RECOGNITION ≠ CELL ACTIVATION
ANTIGEN RECOGNITION BY NAIVE T CELLS REQUIRES ANTIGEN RECOGNITION BY NAIVE T CELLS REQUIRES PRESENTATION VIA MHC MOLECULESPRESENTATION VIA MHC MOLECULES
Recognition/No activation
Recognition/Activation
T CELLT CELL--DEPENDENT BDEPENDENT B CELL ACTIVATIONCELL ACTIVATION
Polysacharides are not presented!
B cell
cytokines
CD4TCR
MHCII+peptide T cell
2
1
T-INDEPENDENT ANTIGENTI-1
T-INDEPENDENT ANTIGENTI-2
Strong crosslinking of BCRcrosslinking of BCR by repetitive polysaccharide or
protein epitopes
Simultaneous activation of BCR and BCR and other receptorsother receptors on B cells (i.e. LPS
binding protein /CD14) induces the B cells to proliferate and differentiate
B cell
B CELL ACTIVATION (extensive receptor-aggregation)(extra activation signal)
B CELL ACTIVATION WITHOUT THE HELP OF T CELLSB CELL ACTIVATION WITHOUT THE HELP OF T CELLS
B CELL ACTIVATION WITHOUT THE HELP OF T CELLSB CELL ACTIVATION WITHOUT THE HELP OF T CELLS
carrier + haptens
hapten
(e.g. DNP: dinitrofenil)
-
+
HAPTEN
molecules that are too small to provoke an immune response unless they are attached to carriers
free haptens haptens attached to a carrier
0
HAPTEN
receptor cross-linking signalization
carrier specific hapten specific carrier + hapten specific
carrier + haptenantibodies
Antibody response generated against a hapten-carrier conjugate
Purified bacterial polysacharides used for vaccination do not lead to long-lasting immunity because the activation of T cells is required for memory B cell formation
Hence the polysaccharide chains are conjugated to protein carriers which can activate T cells
Carrier: CRM197 modified diphteria toxin (toxoid)(a single aminoacid change (Glu Gly) in the toxin can abolish toxicity) The toxoid acts the same way the toxin does; it activates specific T cells and may lead to the production of antitoxins by plasmacells
EXAMPLE (Prevenar - pneumococus vaccine)
polysaccharides of different Streptococcus pneumoniae strains
toxinGlu Gly
toxoid
complex antigen of vaccine
toxoid+
B cellspecific to bacterial polysaccharid
polysacharid
T cellspecific to
toxin/toxoid epitope
BCRTCRMHCII
cytokines,CD40-CD40L
peptide antigen derived
from toxoid
formation of pneumococcus-specific memory B cells
toxoid
Microbial proteins that bind to and activate all the T cells that express a particular set or family of TCR molecules resulting in a polyclonal activation
SUPERANTIGENSSUPERANTIGENS
SUPERANTIGENSSUPERANTIGENS
Microbial proteins that bind to and activate all the T cells that express a particular set or family of TCR molecules resulting in a polyclonal activation.
Interaction is not via the peptide binding cleft of MHC molecule.
Hypotension
Rash
Desquamation
Fever
conventional antigen
monoclonal/oligoclonal
T cell response
1:104 - 1:105
superantigen
polyclonal
T cell response
1:4 - 1:10
Microbial proteins that bind to and activate all the T cells in an individual that express a particular set or family of TCR molecules
107 – 108 / 1011 1010 / 1011activated T cells
SUPERANTIGENSSUPERANTIGENS
SUPERANTIGENSSUPERANTIGENS
Classification Sources
Endogenous
Exogenous
1.Mouse mammary tomor virus (MMTV)2.Epstein-Barr virus (EBV) 1.Staphylococcal enterotoxins (SEs): A, B, C1 to C3, D, E, G to Q 2.Staphylococcal toxic shock syndrome toxin-1 (TSST-1) 3.Staphylococcal exfoliative toxins: exoliatin A, exfoliatin B 4.Staphylococcal enterotoxin-like toxins formed due to recombination within enterotoxin gene cluster: U2, V 5.Streptococcal pyrogenic exotoxins (SPEs): A1 to A4, C, G to M 6.Streptococcal mitogenic exotoxins: SMEZ 7.Streptococcal superantigen :SSA 8.Yersinia pseudotuberculosis: Yersinia pseudotuberculosis-derived mitogen (YAM) 9.Mycoplasma species: Mycoplasma arthritidis-derived mitogen (MAM) 10.Cholera toxin: subunit A of cholera toxin 11.Prevotella intermedia*12.Mycobacterium tuberculosis*•Viral superantigens: (a) Mouse leukemia virus (b) IDDMK1222- Ppol-ENV-U3 (c) HIV-Nef (d) Rabies virus-nucleoside protein
.
ACUTE INFLAMMATIONACUTE INFLAMMATION
AND AND
ACUTE-PHASE RESPONSEACUTE-PHASE RESPONSE
THE INFLAMMATORY RESPONSE THE INFLAMMATORY RESPONSE
A rapid response to an injurious agent that serves to deliver leukocytes and plasma proteins to the site of injury
ACUTE INFLAMMATIONACUTE INFLAMMATION
Infections Trauma Physical and Chemical agents (thermal injury, irradiation, chemicals) Tissue Necrosis Foreign bodies (splinters, dirt, sutures) Hypersensitivity or autoimmune reactions
1. Vascular response:
Increased vascular diameter Increased flood flow.
Endothelial cell activation increased permeability that permits plasma proteins and leukocytes to
leave the circulation and enter the tissue edema increased expression of cell adhesion molecules e.g. E-selectin, ICAM
2. Cellular response:
Migration of leukocytes (diapedesis/extravasation), accumulation, effector functions
MAJOR COMPONENTS OF INFLAMMATION:
TRIGGERS OF ACUTE INFLAMMATION:
• Redness (rubor) • Swelling (tumor) • Heat (calor) • Pain (dolor)• Loss of function (functio laesa)
CLASSICAL SYMPTOMES OF ACUTE INFLAMMATION:
NEUTROPHIL GRANULOCYTES
• 68% of circulating leukocytes, 99% of circulating
granulocytes• Phagocytic cells• Are not present in healthy tissues• Migration elimination of pathogens (enzymes, reactive
oxygen intermediates)
• Main participants of acute inflammatory processes
NEUTROPHIL CHEMOTAXIS
acPGP: N-acetyl Proline-Glycine-Proline – neutrophil chemoattractantMMP: matrix metalloproteinase
MIGRATION OF NEUTROPHILS MIGRATION OF NEUTROPHILS
Neutrophil Transendothelial Migration (Diapedesis)
Pus is a whitish-yellow, yellow, or yellow-brown exudate produced by vertebrates during inflammatory pyogenic bacterial infections. Pus consists of a thin, protein-rich fluid, known as liquor puris, and dead cells.
PUS PUS
CONSEQUENCECONSEQUENCESS OF OF MACROPHAGE AMACROPHAGE ACTIVATIONCTIVATIONSYNTHESIS OF SYNTHESIS OF CCYTOKINESYTOKINES
ACUTE-PHASE REACTIONACUTE-PHASE REACTION
proinflammatory cytokines
hypothalamic control of body temperature
increased ‚set-point’ value
fever
Liver
Mannose binding
lectin/proteinMBL/MBP
Fibrinogen
Serum amyloid protein (SAP)
C-reactive protein (CRP)
UNDER THE INFLUENCE OF IL-6 THE LIVER PRODUCES A BUNCH OF ACUTE-PHASE PROTEINS
ComplementIL-6
ACUTE PHASE REACTIONACUTE PHASE REACTION
ACUTE-PHASE RESPONSEACUTE-PHASE RESPONSEPentraxin family:CRP – opsonization, complement activationSAP – opsonization, complement activation, binding of mannose/galactose
Collectin family:MBL – part of the complement system(SP-A/D – collectins of lungs)
Complement proteins (C1-C9)
Fibrinogen blood clotting
Vasodilation– Prostaglandins (PG), nitric oxide (NO)
Increased vascular permeability– vasoactive amines (histamine, serotonin), C3a and C5a
(complement system), bradykinin, leukotrienes (LT), PAF Chemotactic leukocyte activation
– C3a, C5a, LTB4, chemokines (e.g. IL-8)
Fever• IL-1, IL-6, TNFα, PGE2
Pain• Prostaglandins, bradykinin
Tissue damage• Neutrophil and Macrophage products
–lysosomal enzymes–Reactive oxygen species (ROS)–NO
CHEMICAL MEDIATORS
NSAIDs and Paracetamol:inhibiting COX-1 and COX-2 preventing the synthesis of prostaglandins
NSAIDs and Paracetamol:inhibiting COX-1 and COX-2 preventing the synthesis of prostaglandins
RESOLUTION OF ACUTE INFLAMMATIONRESOLUTION OF ACUTE INFLAMMATION
SEPTIC SHOCKSEPTIC SHOCK
Triggering factors : • systemic infection (bacteraemia)• microbial cell wall products and/or
toxins released from the pathogens
Result: Systemic activation of
neutrophils and macrophages
High level of cytokine (TNF-alpha) production: „cytokine storm”
Excessive inflammatory response
SEPTIC SHOCKSEPTIC SHOCK
The key molecule of the process: TNF-alpha
TNF-alpha and other inflammatory cytokines
capillar permeability blood pressure
DIChigh fever multiorgan failure
Therapy: anti-TNF-alpha antibody
disseminated intravascular
coagulation
DICDICDDisseminated isseminated IIntravascular ntravascular CCoagulationoagulation
• pathologic activation of thrombotic process
• distress of thrombotic process, bleeding
• other causes: snake bite, septic abortion, acute obstetric complications, malignant tumors, leukemias
DIC: DIC: DDisseminated isseminated IIntravascular ntravascular CCoagulationoagulation