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ANTIGENS
an antigen (the generator) when
introduced into a host induces the
formation of specific antibodies and
sensitize...
Definitions
TWO IMPORTANT CHARACTERISTICS 0F AN ANTIGEN
1) IMMUNOGENICITY: The ability of a substance to
stimulate a speci...
Factors Influencing
Immunogenicity
• Foreignness
• Size- Macromolcule
• Chemical Composition
Complexity of structure
• Phy...
CLASSIFICATION OF ANTIGEN
• FOREIGN (OUTSIDE THE HOST)
MICROBE COMPONENTS/ PRODUCTS,
DRUGS
ENVIRONMENTAL ANTIGENS
• AUTOAN...
ANTIGEN EPITOPES ON BACTERIAL CELL
EPITOPES /
ANTIGENIC DETERMINANTS:
Chemical groups on
the antigenic molecule
against wh...
Chemical Nature of
Immunogens
• Proteins– pure or glycoproteins or lipoproteins
• Polysaccharides– pure or lipopolysac
• N...
Types of Antigens
1)T-independent Antigens
(directly stimulates B cells to produce antibodies without
help of T cells)
• P...
Types of Antigens
2) T-dependent antigens
(do not directly stimulate Ab formation without
the help of T cells)
• PROTEINS
...
ANTIGENS
HEPTENS--- small molecules that cannot
induce an immune response unless complexed with
a large carrier molecule l...
Hapten-carrier conjugates
Definition:
Are immunogenic molecules to which
heptans become attached
Native determinants
Hapt...
SUPER ANTIGENS
• Definition:
T-dependent antigens
cause massive activation
of large fraction (25%) of
T cells (polyclonal
...
IMMUNOGLOBULINS:
Structure and Function
Immunoglobulins:Structure and
Function
• DEFINITION: Glycoprotein molecules that are
produced by plasma cells in response ...
Immunoglobulin Structure
• Identical : 2-
Heavy(H) & 2
Light Chains-L
• Disulfide
bonds
Inter-chain
Intra-chain
CH1
VL
C...
Immunoglobulin Structure: on
basis of their A. acid sequence.
• DOMAINS
• Variable (V)
• Constant (C)
Regions
 VL & CL
 ...
Immunoglobulin Fragments:
Structure/Function Relationships
• Fab
Ag binding
Valence = 1
Specificty
determined by VH
and...
Immunoglobulin Fragments:
Structure/Function
Relationships
Ag Binding
Complement Binding Site
Placental Transfer
Binding t...
Human Immunoglobulin Classes
• ON BASIS OF DIFFERENCE IN A.ACID
SEQUENCE IN CONSTANT REGION OF
HEAVY CHAINS:
• IgG - Gamma...
Human Immunoglobulin
Subclasses
• IgG Subclasses
IgG1 - Gamma 1 (1) heavy chains
IgG2 - Gamma 2 (2) heavy chains
IgG3...
Human Immunoglobulin
Light Chain Types
• Kappa ()
• Lambda ()
• Subtypes Lambda light chain:
Lambda 1 (1)
Lambda 2 (...
IgG
• Structure
Monomer (7S)
Subclasses differ in number of disulfide bonds
and length of hinge region
IgG1, IgG2 and Ig...
IgG
• Properties
• Most versatile immunoglobulin
Major serum Ig- 75% of serum Ig
Major Ig in extravascular spaces
Place...
IgM
• Structure
Pentamer
mu chains
Extra domain (CH4)
J chain
C4
J Chain
IgM
Properties
3rd highest serum Ig
First Ig made by
fetus and B cells
Fixes complement
Agglutinating
antibody
Binds ...
IgA
• Structure
Serum - monomer
Secretions (sIgA)
 Dimer –
 J chain
 Secretory
component-
recruited from
serous epith...
Origin of Secretory Component of
sIgA
IgA
Properties
2nd highest serum Ig
1ST
line of defense in mucous membrane
pathogen
Major secretory Ig (Mucosal or Loca...
IgD
• Structure
Monomer
Tail piece
Tail Piece
IgD
Properties
4th highest serum Ig
B cell surface Ig
Does not bind complement
Increased levels in AIDS
IgE
• Structure
Monomer
Extra domain (CH4)
C4
IgE
Properties
Least common serum Ig
 Binds to basophils and mast cells (does not require
Ag binding)
Allergic reaction...
Antibodies eliminate foreign agents in 3 ways
Characteristics of Various Classes of
Immunoglobins
Properties of Antibiotics
MHC COMPLEX
MAJOR HISTOCOMPATIBLE -MHC
COMPLEX
• MHC complex defines uniqueness of the individual
• Part of the genome encoding for MH...
MHC COMPLEX
• MHC 1 ANTIGENS MHC II ANTIGENS
1.Present on the surface Present on the B cell,
of all nucleated cells Macrop...
CYTOKINES
CYTOKINES
• Short acting soluble mediators released during
interaction between lymphocytes, monocytes,
macrophages, inflam...
Important Cytokines
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Antigen

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  1. 1. ANTIGENS an antigen (the generator) when introduced into a host induces the formation of specific antibodies and sensitize T lymphocytes that are reactive against that specific antigen
  2. 2. Definitions TWO IMPORTANT CHARACTERISTICS 0F AN ANTIGEN 1) IMMUNOGENICITY: The ability of a substance to stimulate a specific immune response 2) ANTIGENICITY : The ability of a substance to react specifically with antibodies/ sensitized T cells • HAPTEN: are small molecules that cannot induce an immune response by themselves unless complexed with a large carrier molecule like protein/ polysaccharide • EPITOPE or Antigenic Determinant: that portion of an antigen that combines with the product of a specific Immune response • ANTIBODY (Ab): a specific protein produced in response to an immunogen
  3. 3. Factors Influencing Immunogenicity • Foreignness • Size- Macromolcule • Chemical Composition Complexity of structure • Physical Form Particulate / Soluble Denatured / Native Biodegradability Ag processing by Ag Presenting Cells (APC)
  4. 4. CLASSIFICATION OF ANTIGEN • FOREIGN (OUTSIDE THE HOST) MICROBE COMPONENTS/ PRODUCTS, DRUGS ENVIRONMENTAL ANTIGENS • AUTOANTIGENS THYROGLOBULIN, NUCLEIC ACID, CORNEA COMPONENTS • ISOANTIGENS HISTCOMPATIBILITY TISSUE ANTIGENS BLOOD GROUP ANTIGENS • HETROANTIGENS HETROPHILE ANTIGENS CROSS REACTING MICROBIAL ANTIGENS eg. Streptococcal cell wall antigen cross react with human cardiac and glomerular tissue
  5. 5. ANTIGEN EPITOPES ON BACTERIAL CELL EPITOPES / ANTIGENIC DETERMINANTS: Chemical groups on the antigenic molecule against which antibodies are produced. Eg: bacterial cell– have 100 or more epitopes
  6. 6. Chemical Nature of Immunogens • Proteins– pure or glycoproteins or lipoproteins • Polysaccharides– pure or lipopolysac • Nucleic Acids- poor immunogens or become immunogen when single stranded or complexed with proteins • Lipids– generally non immunogens Some glycolipids and phosopholipids can be immunogenic for T cells and illicit a cell mediated immune response
  7. 7. Types of Antigens 1)T-independent Antigens (directly stimulates B cells to produce antibodies without help of T cells) • POLYSACCHARIDES • Examples Pneumococcal polysaccharide  lipopolysaccharide Flagella
  8. 8. Types of Antigens 2) T-dependent antigens (do not directly stimulate Ab formation without the help of T cells) • PROTEINS • Examples Microbial proteins Non-self or Altered-self proteins
  9. 9. ANTIGENS HEPTENS--- small molecules that cannot induce an immune response unless complexed with a large carrier molecule like protein/ polysac then the hepten alone can react specifically with the antibodies or immune cells produced in response to the hepten-carrier complex. Two types: simple- one antigenic determinant complex- many antigenic determinants Native determinants Haptenic determinants Are immunogenic molecules to which heptans become attached Hapten-carrier conjugates:
  10. 10. Hapten-carrier conjugates Definition: Are immunogenic molecules to which heptans become attached Native determinants Haptenic determinants • Structure native determinants haptenic determinants (created by Heptans)
  11. 11. SUPER ANTIGENS • Definition: T-dependent antigens cause massive activation of large fraction (25%) of T cells (polyclonal response) ---uncontrolled release of cytokines • Examples  Staphylococcal enterotoxins  Staphylococcal toxic shock toxin  Staphylococcal exfoliating toxin  Streptococcal pyrogenic exotoxins
  12. 12. IMMUNOGLOBULINS: Structure and Function
  13. 13. Immunoglobulins:Structure and Function • DEFINITION: Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies • FUNCTIONS: • Recognizing and binding to foreign substances and facilitating their removal • Binding to various cells– phagocytic, lymphocytes mast cells, basophils, placental trophoblast • Increase phagocytosis • Neutralizing toxins and viruses • Activating complement
  14. 14. Immunoglobulin Structure • Identical : 2- Heavy(H) & 2 Light Chains-L • Disulfide bonds Inter-chain Intra-chain CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond
  15. 15. Immunoglobulin Structure: on basis of their A. acid sequence. • DOMAINS • Variable (V) • Constant (C) Regions  VL & CL  VH & CH • Hinge Region • CL 110 A.Acid • VL 110 • VH 11O • CH 33O—44O CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond
  16. 16. Immunoglobulin Fragments: Structure/Function Relationships • Fab Ag binding Valence = 1 Specificty determined by VH and VL Papain Fc Fab • Fc CH2 __CH3 Effector functions
  17. 17. Immunoglobulin Fragments: Structure/Function Relationships Ag Binding Complement Binding Site Placental Transfer Binding to Fc Receptors- M*, Polymorps
  18. 18. Human Immunoglobulin Classes • ON BASIS OF DIFFERENCE IN A.ACID SEQUENCE IN CONSTANT REGION OF HEAVY CHAINS: • IgG - Gamma () heavy chains • IgM - Mu () heavy chains • IgA - Alpha () heavy chains • IgD - Delta () heavy chains • IgE - Epsilon () heavy chains
  19. 19. Human Immunoglobulin Subclasses • IgG Subclasses IgG1 - Gamma 1 (1) heavy chains IgG2 - Gamma 2 (2) heavy chains IgG3 - Gamma 3 (3) heavy chains IgG4 - Gamma 4 (4) heavy chains • IgA subclasses IgA1 - Alpha 1 (1) heavy chains IgA2 - Alpha 2 (2) heavy chains
  20. 20. Human Immunoglobulin Light Chain Types • Kappa () • Lambda () • Subtypes Lambda light chain: Lambda 1 (1) Lambda 2 (2) Lambda 3 (3) Lambda 4 (4)
  21. 21. IgG • Structure Monomer (7S) Subclasses differ in number of disulfide bonds and length of hinge region IgG1, IgG2 and IgG4 IgG3
  22. 22. IgG • Properties • Most versatile immunoglobulin Major serum Ig- 75% of serum Ig Major Ig in extravascular spaces Placental transfer – Does not require Ag binding ( IgG2) Fixes complement ( IgG4) Binds to Fc receptors ( IgG2, IgG4)  Phagocytes - opsonization  K cells - ADCC
  23. 23. IgM • Structure Pentamer mu chains Extra domain (CH4) J chain C4 J Chain
  24. 24. IgM Properties 3rd highest serum Ig First Ig made by fetus and B cells Fixes complement Agglutinating antibody Binds to Fc receptors
  25. 25. IgA • Structure Serum - monomer Secretions (sIgA)  Dimer –  J chain  Secretory component- recruited from serous epith. J ChainSecretory Piece
  26. 26. Origin of Secretory Component of sIgA
  27. 27. IgA Properties 2nd highest serum Ig 1ST line of defense in mucous membrane pathogen Major secretory Ig (Mucosal or Local Immunity)  Tears, saliva, gastric and pulmonary secretions Does not fix complement (unless aggregated) Binds to Fc receptors on some cells Neutralizes viruses and toxins
  28. 28. IgD • Structure Monomer Tail piece Tail Piece
  29. 29. IgD Properties 4th highest serum Ig B cell surface Ig Does not bind complement Increased levels in AIDS
  30. 30. IgE • Structure Monomer Extra domain (CH4) C4
  31. 31. IgE Properties Least common serum Ig  Binds to basophils and mast cells (does not require Ag binding) Allergic reactions Parasitic infections (Helminths)  Binds to Fc receptor on Eosinophils  Activation of macrophages--- ADCC Does not fix complement
  32. 32. Antibodies eliminate foreign agents in 3 ways
  33. 33. Characteristics of Various Classes of Immunoglobins
  34. 34. Properties of Antibiotics
  35. 35. MHC COMPLEX
  36. 36. MAJOR HISTOCOMPATIBLE -MHC COMPLEX • MHC complex defines uniqueness of the individual • Part of the genome encoding for MHC antigens– clustered on a small segment of chromosome 6– CONSTITUTE HLA COMPLEX • At least 20 different genes encode for MHC PROTEINS • Variety of MHC proteins exist in humans • Identical twins have same MHC molecules • All family members have a mixture of similar and different MHC molecules • Functions: • The principle function is to bind peptide fragments of foreign proteins and present it to antigen specific T cell. • Immune recognition • Interaction between B and T and other cells • Rejection of allograft
  37. 37. MHC COMPLEX • MHC 1 ANTIGENS MHC II ANTIGENS 1.Present on the surface Present on the B cell, of all nucleated cells Macrophages and of the body, platelets activated T cells 2. Bind Ag/ peptide Bind Ag/ peptides endogenously produce exogenously produced eg. viral proteins then processed within cell after phagocytosis 3. Present Ag to CD8 - Present Ag to CD4 cells- TC cells TH Cells CLASS1 AND 11 GENES ENCODE CELL SURFACE GLYCOPROTEINS AND CLASS III GENES FOR COMPONENTS OF COMPLEMENT SYSTEM
  38. 38. CYTOKINES
  39. 39. CYTOKINES • Short acting soluble mediators released during interaction between lymphocytes, monocytes, macrophages, inflammatory cells and endothelial cells • Concerned with induction and regulation of immune response • Hormone like peptides or glycopeptides with wide spectrum of effects • PROPERTIES • Individual cytokines produced by different cell types eg. IL-I,TNF -- PRODUCED BY VIRTUALLY ALL CELLS • Cytokines have PLEOTROPIC effect– act on many cell types—IL2 ---T cells, B, NK CELLS • Cytokines produce their effect by combining with high affinity receptors on the target cell eg:IL2 activate T cells by binding to IL2 receptor • They can act on the same cell that produces it eg IL 2 produced by activated T cell promote T cell growth
  40. 40. Important Cytokines

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