1 Antigens Hugh B Fackrell 6142021 2 Assigned
1 Antigens Hugh B. Fackrell 6/14/2021
2 ä Assigned Reading ä Content Outline ä Performance Objectives ä Key terms ä Key Concepts ä Short Answer Questions 6/14/2021
3 ASSIGNED READING ä Chapter 4 pp 87 -106 6/14/2021
4 OUTLINE ä ä Immunogenicity vs antigenicity Factors that influence immunogenicity ä immunogen contributions biological system contributions ä ä ä Epitopes ä ä ä B cell epitopes T cell epitopes Haptens Mitogens 6/14/2021
5 Definitions ä Antigen - a substance recognized by T and B cell receptors ä Immunogen - a substance capable of eliciting immune response ä Hapten - a substance of low molecular weight, that can bind antibodies but induce response only if covalently attached to large carrier Klein, 1992 6/14/2021
6 Definitions (cont) ä Antigenic Determinant: Specific sequence of amino acids that combine with receptor ä Epitope: an antigenic determinant on the surface of a molecule ä Cryotope: An antigenic determinant that is buried within a molecule and thus is unavailable in the intact molecule 6/14/2021
7 Immunogen vs Antigen ä Immunogen ä Any compound that triggers the immune response ä Antigen ä Any compound that combines with the products of an immune response 6/14/2021
8 Factors Influencing Immunogenicity ä immunogen contributions ä biological system contributions 6/14/2021
9 Immunogen Contributions ä Chemical nature ä Chemical complexity ä Molecular size ä Conformation ä Foreigness 6/14/2021
10 Effects of Biological System on Immunogenicity ä Genotype ä Dose of Immunogen ä Route of Injection ä Adjuvants 6/14/2021
11 Genotypic Influences ä Immune Responsiveness ä Some strains of inbred mice respond to specific immunogen (high responders) ä Other strains do not (low responders) ä Hybrids of above have intermediate response ä Structure of MHC receptors on cell membrane 6/14/2021
12 MHC Receptors 6/14/2021
13 Dose of Immunogen ä Tolerance: Specific non response to an immunogen ä Dose dependent ä Too low- no effect ä Low dose: Tolerize T cell ä High dose: Tolerize B cells 6/14/2021
14 Mitcheson Tolerance Exp 200 - % 100 - Response Immunity Low Zone Tolerance High Zone Tolerance 0 - log [antigen injected] 6/14/2021
15 Tolerogenic vs Immunogenic ä Immunogenicity ä antigens first processed by APC ä APC reacts with lymphocyte ä response ä Tolerogenicity ä antigens react directly with lymphocyte ä NO response Immunogenicity requires co stimulation 6/14/2021
16 Route of Injection ä Parenteral injection ä other than digestive tract ä intravenous, intradermal, sucutaneous, intramuscular, intraperitioneal ä Exposure to different lymphocyte populations ä intravenous - spleen ä subcutaneous- lymph nodes 6/14/2021
17 Adjuvants ä Substances that enhance immunogenicity of an antigen ä alum ä Freund’s ( contains Mycobacterium) ä Mechanisms ä prolong life of antigen ä enhance co-stimulatory signals ä nonspecific multiplication of lymphocyte ä granuloma formation 6/14/2021
18 Haptens ä Antigenic but not immunogenic ä small molecules eg Di. Nitro. Phenol ä Flexible molecules eg gelatin ä When linked to a carrier molecule becomes immunogenic ä Hapten- Carrier conjugates ä Hapten immunodominant determinant 6/14/2021
19 Epitopes ä Size ä Specificity ä Affinity 6/14/2021
20 Construction of Epitope ä Continuous ä stretch of contiguous residues endowed with distinctive conformational features ä Discontinous ä group of residues that are non contiguous in the sequence but are brought together by the folding of the polypeptide chain ä Klein 1992 6/14/2021
21 B cell Epitopes 6/14/2021
22 Immunoglobulin: B cell receptor 6/14/2021
23 Antigen - Antibody binding ä Hydrogen bonds ä Electrostatic forces ä Van der Walls interactions ä Hydrophobic interactions 6/14/2021
24 6/14/2021
25 T cell Epitopes 6/14/2021
26 Mitogens 6/14/2021
27 The End 6/14/2021
28 Molecular Dissection of Proteinaceous Antigens Created Maria Sawicki Updated Hugh B. Fackrell Dec 1997 6/14/2021
29 X - Ray Crystallography ä Crystallized Antigen or Antigen - Antibody Complex ä Electron Density Map of the Molecule ä Three Dimensional Images 6/14/2021
30 Construction of Epitope ä Continuous ä stretch of contiguous residues endowed with distinctive conformational features ä Discontinous ä group of residues that are non contiguous in the sequence but are brought together by the folding of the polypeptide chain ä Klein 1992 6/14/2021
31 ANTIGEN RECOGNITION SYSTEMS ä Immunoglobulins ä intact antigen is presented conformational epitopes with several ä T cell receptors ä “processed antigen” is presented and can be recognized only in complex with Major HIstocompability Complex. 6/14/2021
32 Synthetic Peptides ä Overlapping Epitopes ä Immunodominance Benjamini , 1984 6/14/2021
33 Prediction of antigenicity ä Region accesibility ä Novotny 1988 ä Segmental mobility ä Westhof et al 1984, Tainer et al 1985 ä Relative hydrophilicity ä Hoop and Woods 1983, Hoop 1986 ä Chain termination ä Thorton and Sibanda 1983 ä Segmental variability ä Jemmerson and Parerson 1985 6/14/2021
34 Epitope Mapping Cross-reactivity studies Native Protein and Peptide Fragments Synthetic Peptides Closely Related Proteins ä Van Renmortel, 1988 6/14/2021
35 Studies of Native Proteins and Peptide Fragments ä Conformational influences ä Native protein derivatives ä Overlapping peptide sequences ä Derivatives of active peptides ä Synthetic peptides Atassi, 1978 6/14/2021
36 The End 6/14/2021
37 Performance Objectives Key terms, concepts short answers 6/14/2021
38 KEY TERMS ä Accessibility, antigenic determinants, antigenic site mobility, ä antigenicity, continous (linear) determinants), discontinous (conformational) determinants ä epitopes, agreotopes, haptens, immunodominance, immunogenicity 6/14/2021
39 KEY CONCEPTS ä Differentiate between and antigen's inductive and reactive abilities. ä Explain the factors that bestow immunogenicity on molecules ä Describe the discrete and distinctive sites on and antigen that are recognized by a B cell Immunoglobulin 6/14/2021
40 KEY CONCEPTS ä Describe the discrete and distinctive sites on and antigen that are recognized by a T cell receptor ä Describe the discrete and distinctive sites on and antigen that are recognized by the Major Histocompatability Complex ä Discuss some important characteristics of protein antigenic determinants 6/14/2021
41 SHORT ANSWER QUESTIONS 6/14/2021
42 ä Differentiate between immunogenicity and antigenicity. ä All immunogens are antigens but all antigens are not immunogens. Explain with the use of specific examples. ä An entire microbe or molecule does not induce and immune response. Explain. ä Irrespective of the number of epitopes that a molecule has, the immune response is biased and sees what it wants to see. Explain. 6/14/2021
43 ä Haptens are usually coupled to a carrier molecule before they are immunogenic. How can you demonstrate that the selected immunoglobulins are specific for the hapten and not for the carrier? ä As a corollory, would you expect ALL of the antibodies to be specific for the hapten? explain. 6/14/2021
44 ä Why is the definition of an antigen considered to be an operational definition. ä Differentiate between epitopes and agreotopes. ä Differentiate between epitopes recognized by B cell receptor and epitopes recognized by T cell receptors. 6/14/2021
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