Antigens, haptens and immunogens
<ul><li>Definitions: </li></ul><ul><li>An antigen  is any substance that react with T or B lymphocytes </li></ul><ul><ul><...
<ul><li>Immunogens  are substances that generate immune response </li></ul>
<ul><li>Haptens  are small molecules which could never induce an immune response unless coupled to a carrier molecule (for...
Antibody-Antigen Interactions <ul><li>Binding of antibody to antigen is dependent on  </li></ul><ul><ul><li>hydrogen bonds...
What is an Epitope <ul><li>An epitope is the small site on the antigen which is recognized by the antibody. </li></ul><ul>...
<ul><li>Antigenic determinant is a cluster of epitopes  on the surface of an antigen. </li></ul><ul><li>Antigen has  sever...
 
 
 
<ul><li>The affinity  or strength of binding of antigen and antibody depends on  closeness of fitting . </li></ul><ul><li>...
<ul><li>Avidity  is the strength of binding two molecules or cells to one another at multiple sites. </li></ul><ul><li>It ...
<ul><li>The specificity of antigen recognition by an antibody is not  absolute   </li></ul><ul><li>Cross-reactivity  is du...
Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreignness </li></ul><ul><li>Size </li></ul><ul>...
Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreigness </li></ul><ul><li>Size </li></ul><ul><...
Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreigness </li></ul><ul><li>Size </li></ul><ul><...
Factors Influencing Immunogenicity Contribution of the Biological System <ul><li>Genetics </li></ul><ul><ul><li>Species </...
Factors Influencing Immunogenicity Method of Administration <ul><li>Dose </li></ul><ul><li>Route </li></ul><ul><ul><li>Sub...
Chemical Nature of Immunogens <ul><li>Proteins </li></ul><ul><li>Polysaccharides </li></ul><ul><li>Nucleic Acids </li></ul...
Types of Antigens T-independent <ul><li>Polysaccharides </li></ul><ul><li>Properties </li></ul><ul><ul><li>Polymeric struc...
Types of Antigens T-dependent <ul><li>Proteins </li></ul><ul><li>Structure </li></ul><ul><li>Examples </li></ul><ul><ul><l...
What Does The B Cell  Immunoglobulin (Ig) Receptor Recognize? <ul><li>Proteins (conformational determinants, denatured or ...
What Does the  αβ T Cell Receptor (TCR) Recognize? <ul><li>Only  fragments  of proteins (peptides) associated with MHC mol...
Antigenic Determinants  Recognized by B cells and Ab <ul><li>Composition </li></ul><ul><ul><li>Proteins, polysaccharides, ...
Antigenic Determinants  Recognized by B cells and Ab <ul><li>Composition </li></ul><ul><li>Size </li></ul><ul><li>Number <...
Antigenic Determinants Recognized by T cells <ul><li>Composition </li></ul><ul><ul><li>Proteins (some lipids) </li></ul></...
Conventional Antigen  Superantigen αC βC CHO CHO CHO CHO βV αV α2 β2 β1 α1 CHO CHO CHO αC βC CHO CHO CHO CHO βV αV α2 β2 β...
Superantigens <ul><li>Proteins produced by pathogens </li></ul><ul><li>Not  processed by antigen presenting cells </li></u...
Superantigens <ul><li>Definition </li></ul><ul><li>Examples </li></ul><ul><ul><li>Staphylococcal enterotoxins </li></ul></...
Antigen presenting cells (APC) <ul><li>Cells with the capacity to capture, process  and present antigenic peptides to T ce...
Pathway of Antigen Presentation  by Antigen-Presenting Cells
CD4+ T cells <ul><li>T cells with CD4 marker (glycoprotein) </li></ul><ul><li>70% of T cells in the periphery  </li></ul><...
Differences b/w Th1 and Th2 cells <ul><li>Produces type 1 cytokines </li></ul><ul><ul><li>IL-2, IFN-  , TNF-  , TNF-  <...
T cells <ul><li>T cell receptors (TCR) – Ag specific </li></ul><ul><li>Glycoproteins CD4 (helper T cells) or CD8 (cytotoxi...
CD4+  T cells <ul><li>Helper T cells     involved in Ab production </li></ul><ul><li>Recognition of  “exogenous Ag” </li>...
CD8+ T cells <ul><li>Cytotoxic T cells    cell killing </li></ul><ul><li>Recognition of “endogenous Ag” </li></ul><ul><ul...
All T cells are “Antigen specific” <ul><li>Mediated by “T cell receptor”    TCR </li></ul><ul><ul><li>Surface molecule an...
T cell Membrane   T Cell Receptor Antigen Recognition
Antibody Structure Figure 13.3, p. 251 TCR like this portion of Ab Complement Binding Site Phagocyte Receptor Binding Site
TCR Recognizes its Epitope Only in the Context of MHC <ul><li>CD4 TCR – peptide/MHC Class II </li></ul><ul><li>CD8 TCR – p...
APC = e.g., Macrophage TCR Peptide Antigen CD4 CD4 T Cell MHC Class II
MHC Class I and Class II <ul><li>MHC I on all cells      MHC II on APC </li></ul><ul><li>Bind Ag    only small  peptides...
Cytotoxic T cells <ul><li>T cells that express CD8 molecule on their surface </li></ul><ul><li>30% of T cells in the perip...
Humoral response:  B cells <ul><li>Stimulated by  T-dependent antigens  (help from TH cells) </li></ul><ul><li>APCs with c...
Antibody-mediated effector mechanisms
Points Concerning Antigen Processing and Presentation <ul><li>1. Location of pathogen  </li></ul><ul><li>viruses in cytoso...
<ul><li>Thank you </li></ul>
Upcoming SlideShare
Loading in …5
×

Antigens, hapteins, immunogens lectures 10.1.06

8,480 views

Published on

Published in: Technology
2 Comments
16 Likes
Statistics
Notes
No Downloads
Views
Total views
8,480
On SlideShare
0
From Embeds
0
Number of Embeds
84
Actions
Shares
0
Downloads
1,073
Comments
2
Likes
16
Embeds 0
No embeds

No notes for slide
  • Antibody-antigen Interactions Antibodies and antigens can both be multivalent.
  • The flexibility of the hinge region improves the efficiency of antigen binding and cross-linking.
  • Schematic Drawing of a typical antibody molecule. There are two identical light chains and two identical heavy chains. The heavy chain determines the antibody subclass. We will use the IgG molecule in lab.
  • Antigens, hapteins, immunogens lectures 10.1.06

    1. 1. Antigens, haptens and immunogens
    2. 2. <ul><li>Definitions: </li></ul><ul><li>An antigen is any substance that react with T or B lymphocytes </li></ul><ul><ul><li>simple to macromolecules e .g. carbohydrates, phospholiplids, nucleic acids and proteins . </li></ul></ul>
    3. 3. <ul><li>Immunogens are substances that generate immune response </li></ul>
    4. 4. <ul><li>Haptens are small molecules which could never induce an immune response unless coupled to a carrier molecule (foreign protein) </li></ul><ul><ul><li>e.g. dinitrophenyl , aminobenzene sulphonate , arsonate </li></ul></ul><ul><li>Haptein-carrier molecule , unlike free haptein, can acts as an immunogen. </li></ul>
    5. 5. Antibody-Antigen Interactions <ul><li>Binding of antibody to antigen is dependent on </li></ul><ul><ul><li>hydrogen bonds, electrostatic attractions and Van der Waals attractions. </li></ul></ul><ul><li>These bonds are weak compared to covalent bonds but the large number of weak bonds result in a stable complex. </li></ul><ul><li>Antibody-antigen binding is reversible. </li></ul>
    6. 6. What is an Epitope <ul><li>An epitope is the small site on the antigen which is recognized by the antibody. </li></ul><ul><li>Usually between one and six sugars or amino acids on the surface of the antigen. </li></ul><ul><li>Antibody Uniqueness: </li></ul><ul><li>B-cells produce somewhere between 1 x 10 8 </li></ul><ul><li>and 1 x 10 10 IgG antibodies with different binding sites. </li></ul>
    7. 7. <ul><li>Antigenic determinant is a cluster of epitopes on the surface of an antigen. </li></ul><ul><li>Antigen has several determinants each structurally different from each other. </li></ul><ul><li>A monoclonal antibody reacts with only one determinant on the same antigen. </li></ul>
    8. 11. <ul><li>The affinity or strength of binding of antigen and antibody depends on closeness of fitting . </li></ul><ul><li>It refers to strength of association between an individual epitope and a paratope high affinity antibodies bind strongly to antigen. </li></ul>
    9. 12. <ul><li>Avidity is the strength of binding two molecules or cells to one another at multiple sites. </li></ul><ul><li>It is determined by </li></ul><ul><li> heterogeneity of antibodies in serum </li></ul><ul><li> heterogeneity of antigenic determinants </li></ul><ul><li> ‘bonus effect’ = k avid = k1 x k2 </li></ul><ul><li>Avidity – measure of the functional affinity of an antiserum for the whole antigen. </li></ul>
    10. 13. <ul><li>The specificity of antigen recognition by an antibody is not absolute </li></ul><ul><li>Cross-reactivity is due to antiserum reacting with a partially related antigen. </li></ul><ul><li>Monoclonal antibodies are directed towards a single epitope  less cross – reactivity. </li></ul>
    11. 14. Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreignness </li></ul><ul><li>Size </li></ul><ul><li>Chemical Composition </li></ul><ul><ul><li>Primary Structure </li></ul></ul><ul><ul><li>Secondary Structure </li></ul></ul><ul><ul><li>Tertiary Structure </li></ul></ul><ul><ul><li>Quarternary Structure </li></ul></ul>Conformational determinants Sequence determinants
    12. 15. Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreigness </li></ul><ul><li>Size </li></ul><ul><li>Chemical Composition </li></ul><ul><li>Physical Form </li></ul><ul><ul><li>Particulate > Soluble </li></ul></ul><ul><ul><li>Denatured > Native </li></ul></ul>
    13. 16. Factors Influencing Immunogenicity Contribution of the Immunogen <ul><li>Foreigness </li></ul><ul><li>Size </li></ul><ul><li>Chemical Composition </li></ul><ul><li>Physical Form </li></ul><ul><li>Degradability </li></ul><ul><ul><li>Ag processing by Ag Presenting Cells (APC) </li></ul></ul>
    14. 17. Factors Influencing Immunogenicity Contribution of the Biological System <ul><li>Genetics </li></ul><ul><ul><li>Species </li></ul></ul><ul><ul><li>Individual </li></ul></ul><ul><ul><ul><li>Responders vs Non-responders </li></ul></ul></ul><ul><li>Age </li></ul>
    15. 18. Factors Influencing Immunogenicity Method of Administration <ul><li>Dose </li></ul><ul><li>Route </li></ul><ul><ul><li>Subcutaneous > Intravenous > Intragastric </li></ul></ul><ul><li>Adjuvant </li></ul><ul><ul><li>Substances that enhance an immune response to an Ag </li></ul></ul>
    16. 19. Chemical Nature of Immunogens <ul><li>Proteins </li></ul><ul><li>Polysaccharides </li></ul><ul><li>Nucleic Acids </li></ul><ul><li>Lipids </li></ul><ul><ul><li>Some glycolipids and phosopholipids can be immunogenic for T cells and illicit a cell mediated immune response </li></ul></ul>
    17. 20. Types of Antigens T-independent <ul><li>Polysaccharides </li></ul><ul><li>Properties </li></ul><ul><ul><li>Polymeric structure </li></ul></ul><ul><ul><li>Polyclonal B cell activation </li></ul></ul><ul><ul><ul><li>Yes -Type 1 (TI-1) </li></ul></ul></ul><ul><ul><ul><li>No - Type 2 (TI-2) </li></ul></ul></ul><ul><ul><li>Resistance to degradation </li></ul></ul><ul><li>Examples </li></ul><ul><ul><li>Pneumococcal polysaccharide, lipopolysaccharide </li></ul></ul><ul><ul><li>Flagella </li></ul></ul>
    18. 21. Types of Antigens T-dependent <ul><li>Proteins </li></ul><ul><li>Structure </li></ul><ul><li>Examples </li></ul><ul><ul><li>Microbial proteins </li></ul></ul><ul><ul><li>Non-self or Altered-self proteins </li></ul></ul>
    19. 22. What Does The B Cell Immunoglobulin (Ig) Receptor Recognize? <ul><li>Proteins (conformational determinants, denatured or proteolyzed determinants) </li></ul><ul><li>Nucleic acids </li></ul><ul><li>Polysaccharides </li></ul><ul><li>Some lipids </li></ul><ul><li>Small chemicals (haptens) </li></ul>
    20. 23. What Does the αβ T Cell Receptor (TCR) Recognize? <ul><li>Only fragments of proteins (peptides) associated with MHC molecules on surface of cells </li></ul><ul><li>Helper T cells (Th) recognize peptide associated with MHC class II molecules </li></ul><ul><li>Cytotoxic T cells (Tc) recognize peptide associated with MHC class I molecules </li></ul>
    21. 24. Antigenic Determinants Recognized by B cells and Ab <ul><li>Composition </li></ul><ul><ul><li>Proteins, polysaccharides, nucleic acids </li></ul></ul><ul><ul><li>Sequence (linear) determinants </li></ul></ul><ul><ul><li>Conformational determinants </li></ul></ul><ul><li>Size </li></ul><ul><ul><li>4-8 residues </li></ul></ul>
    22. 25. Antigenic Determinants Recognized by B cells and Ab <ul><li>Composition </li></ul><ul><li>Size </li></ul><ul><li>Number </li></ul><ul><ul><li>Limited (immunodominant epitopes) </li></ul></ul><ul><ul><li>Located on the external surfaces of the Ag </li></ul></ul>Fe
    23. 26. Antigenic Determinants Recognized by T cells <ul><li>Composition </li></ul><ul><ul><li>Proteins (some lipids) </li></ul></ul><ul><ul><li>Sequence determinants </li></ul></ul><ul><ul><ul><li>Processed </li></ul></ul></ul><ul><ul><ul><li>MHC presentation (lipid presentation by MHC-like CD1) </li></ul></ul></ul><ul><li>Size </li></ul><ul><ul><li>8 -15 residues </li></ul></ul><ul><li>Number </li></ul><ul><ul><li>Limited to those that can bind to MHC </li></ul></ul>
    24. 27. Conventional Antigen Superantigen αC βC CHO CHO CHO CHO βV αV α2 β2 β1 α1 CHO CHO CHO αC βC CHO CHO CHO CHO βV αV α2 β2 β1 α1 CHO CHO CHO MHC Class II T cell receptor Antigen Super antigen T lymphocyte Antigen presenting cell
    25. 28. Superantigens <ul><li>Proteins produced by pathogens </li></ul><ul><li>Not processed by antigen presenting cells </li></ul><ul><li>Intact protein binds to variable region of β chain on TCR of T cells and to MHC class II on antigen presenting cells (APC) </li></ul><ul><li>Large numbers of activated T cells release cytokines having pathological effects </li></ul>
    26. 29. Superantigens <ul><li>Definition </li></ul><ul><li>Examples </li></ul><ul><ul><li>Staphylococcal enterotoxins </li></ul></ul><ul><ul><li>Staphylococcal toxic shock toxin </li></ul></ul><ul><ul><li>Staphylococcal exfoliating toxin </li></ul></ul><ul><ul><li>Streptococcal pyrogenic exotoxins </li></ul></ul>
    27. 30. Antigen presenting cells (APC) <ul><li>Cells with the capacity to capture, process and present antigenic peptides to T cells </li></ul><ul><li>Antigens are presented in the context of MHC class I or II </li></ul><ul><li>Also deliver co-stimulatory signal (signal II) to T cells leading to proper activation </li></ul><ul><li>Only APCs can activate a naïve T cell </li></ul><ul><ul><li>Dendritic cells, Macrophages, B cells </li></ul></ul>
    28. 31. Pathway of Antigen Presentation by Antigen-Presenting Cells
    29. 32. CD4+ T cells <ul><li>T cells with CD4 marker (glycoprotein) </li></ul><ul><li>70% of T cells in the periphery </li></ul><ul><li>T helper cells </li></ul><ul><li>Play central role in modulating cellular immunity via secretion of cytokines that modulate: </li></ul><ul><ul><li>B cell activation </li></ul></ul><ul><ul><li>Immunoglobulin secretion (quality) </li></ul></ul><ul><ul><li>Macrophage and dendritic cell activation </li></ul></ul><ul><ul><li>Cellular chemotaxis and inflammation </li></ul></ul><ul><li>Th1 versus Th2 cells </li></ul>
    30. 33. Differences b/w Th1 and Th2 cells <ul><li>Produces type 1 cytokines </li></ul><ul><ul><li>IL-2, IFN-  , TNF-  , TNF-  </li></ul></ul><ul><li>Activates macrophages and DCs for intracellular killing of pathogens </li></ul><ul><li>Mediates CMI </li></ul><ul><li>Produces type 2 cytokines </li></ul><ul><ul><li>IL-4, IL-5, IL-10, IL-13 </li></ul></ul><ul><li>Provides help to B cells in antibody response </li></ul><ul><li>Mediates allergy and immunity to extracellular pathogens, including parasites </li></ul>Th1 cell Th2 cell
    31. 34. T cells <ul><li>T cell receptors (TCR) – Ag specific </li></ul><ul><li>Glycoproteins CD4 (helper T cells) or CD8 (cytotoxic T cells) </li></ul>CD4 T cell or helper T cell CD8 T cell or cytotoxic T cell CD4 CD8 TCR TCR
    32. 35. CD4+ T cells <ul><li>Helper T cells  involved in Ab production </li></ul><ul><li>Recognition of “exogenous Ag” </li></ul><ul><ul><li>Bacteria </li></ul></ul><ul><ul><li>Extracellular Ag </li></ul></ul><ul><li>Recognize MHC class II molecule </li></ul><ul><ul><li>Present on “ antigen presenting cells ” = APC </li></ul></ul><ul><ul><li>e.g. Macrophages, Dendritic Cells, B cells </li></ul></ul>
    33. 36. CD8+ T cells <ul><li>Cytotoxic T cells  cell killing </li></ul><ul><li>Recognition of “endogenous Ag” </li></ul><ul><ul><li>Virus infected cells </li></ul></ul><ul><ul><li>Cancerous cells </li></ul></ul><ul><li>Recognize MHC class I molecule </li></ul><ul><ul><li>Present on all cells </li></ul></ul>
    34. 37. All T cells are “Antigen specific” <ul><li>Mediated by “T cell receptor”  TCR </li></ul><ul><ul><li>Surface molecule analogous to part of Ab </li></ul></ul><ul><li>Diversity is generated by rearrangement of TCR gene locus </li></ul>
    35. 38. T cell Membrane   T Cell Receptor Antigen Recognition
    36. 39. Antibody Structure Figure 13.3, p. 251 TCR like this portion of Ab Complement Binding Site Phagocyte Receptor Binding Site
    37. 40. TCR Recognizes its Epitope Only in the Context of MHC <ul><li>CD4 TCR – peptide/MHC Class II </li></ul><ul><li>CD8 TCR – peptide/MHC Class I </li></ul>
    38. 41. APC = e.g., Macrophage TCR Peptide Antigen CD4 CD4 T Cell MHC Class II
    39. 42. MHC Class I and Class II <ul><li>MHC I on all cells  MHC II on APC </li></ul><ul><li>Bind Ag  only small peptides </li></ul><ul><li>As an individual you make a small number of different kinds of MHC I and MHC II </li></ul><ul><li>Encoded by stable genes inherited ; NOT generated by rearrangements </li></ul><ul><li>But in the population there are lots of genetic variants of MHC I and MHC II </li></ul><ul><ul><li>Important in transplants </li></ul></ul><ul><ul><li>Hence the name  “Major Histocompatability Complex” </li></ul></ul>
    40. 43. Cytotoxic T cells <ul><li>T cells that express CD8 molecule on their surface </li></ul><ul><li>30% of T cells in the periphery </li></ul><ul><li>Destroy cells infected by intracellular pathogens and cancer cells </li></ul><ul><li>Class I MHC molecules (nucleated body cells) expose foreign proteins </li></ul><ul><li>T C cell releases perforin and granzymes , proteins that form pores in the target cell membrane; causing cell lysis and/or apoptosis </li></ul>
    41. 44. Humoral response: B cells <ul><li>Stimulated by T-dependent antigens (help from TH cells) </li></ul><ul><li>APCs with class II MHC proteins process and present antigen to CD4+ T cells (helper cells) </li></ul><ul><li>Helper T cell become activated </li></ul><ul><li>Activated T cell secretes cytokines that in turn activate B cell </li></ul><ul><li>B cell differentiates into effector and memory (plasma) cells and produce antibodies </li></ul>
    42. 45. Antibody-mediated effector mechanisms
    43. 46. Points Concerning Antigen Processing and Presentation <ul><li>1. Location of pathogen </li></ul><ul><li>viruses in cytosol, MHC class I pathway, Tc response </li></ul><ul><li>extracellular bacteria, MHC class II pathway, Th2 response, Ab formation </li></ul><ul><li>intracellular bacteria, MHC class II pathway, Th1 response </li></ul>
    44. 47. <ul><li>Thank you </li></ul>

    ×