Antigen Structure and Immunogenicity

Folder Title: Antigens (With TP Slides)

Updated: September 17, 2013

Antigen Recognition by the Specific Immune System: Recognition by B-cell and T-cell Receptors

Antigen (Ag): Binds specifically to an antibody binding site (Ab), or to a T-cell receptor (TCR) Immunogen: Binds specifically to an antibody binding site or to a T-cell receptor,

and generates a humoral or cellular immune response.

All immunogens must be antigens, Not all antigens can generate a response.

Haptens and Epitopes

Haptens: Small organic molecule (e.g. 1-Fluoro-2,4-dinitrobenzene) Not Immunogenic by themselves Can be immunogenic when attached to an immunogenic macromolecular carrier The Anti-hapten antibody so generated will bind the Hapten Epitope: A region of a macromolecular antigen that is actually an antigenic determinant, a molecular sub-region that is actually recognized and bound by an Antibody or T-Cell Receptor

Fig.

4-6b Kuby 3rd Ed

Antigen-Antibody Complementarity

Antibody Light Chain Variable Region AgAb Sep Influenza Virus Antigen Antibody Heavy ChainVariable Region

Fig.

4-6a Kuby 3rd Ed

Antigen - Antibody Binding

Antibody Light Chain Variable Region AgAb Kiss Influenza Virus Antigen Antibody Heavy Chain Variable Region

Prot2nd

Primary sequential epitopes in sperm whale myoglobin

Conformational (non-sequential) Epitope in Hen Egg White Lysozyme.

(Colors show amino acid side chains contacting the two different chains of the antibody, or contacting both chains. Antibody structure to be covered later)

What Determines Immunogenicity of an Antigen?

1. Properties of the immunogen (See detailed breakdown next slide) 2. Properties of the Host (Slides 12 and 18) a. Genetic b. Physiological 3. Mode of Antigen Exposure

ImGenFx1

ImGenFx2

Ag&MHCa

Ag&MHCb

Ag&MHCc

Ag&MHCd

Ag&MHC

ImGenFx3

ImAdmin

Conformational Properties of Epitopes for Antibodies

80 64

Hen Egg-White Lysozyme: Conformations of Sequence 62 to 80

Anti-hapten Antibodies

See Figure 4-1 p. 77 Kuby, 6 th Edition

AbHapten

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Fill-in-the Blank” Question:

When a small organic molecule is made immunogenic by attaching it to a macromolecule it is called a

__ __ __ __ __ __

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What is this molecular model showing?

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Ran k

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Immunogenicity of Antigens is Controlled by the Nature of the Antigen, the Genetics of the Host, and the Mode of Immunogen Exposure. Give an example of what is meant by “Mode of Immunogen or Antigen Exposure”

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AgByB&Ta

AgByB&Tb

AgByB&T

Conformational (non sequential) Epitope in Hen Egg White Lysozyme.

Antigens in Immunologically-Based Clinical Diagnosis and Pathology

Cancer Antigens in Diagnosis of Cancer Carcino-Embryonic Antigen (CEA) Prostate Specific Antigen (PSA) Ovarian Cancer Antigen (CA 125) Whole-body Imaging of Metastatic Colon Carcinoma A33 Antigen Anti-Human Chorionic Gonadotropin Pregnancy Test (Early Home Pregnancy Test) Type II Allergic Hypersensitivity Blood Group Antigens in Transfusions Hemolytic Disease of New-Borns: Rh Antigen incompatibility Super-Antigens in Toxic Shock Syndrome

Med&Ags

Antigens in Immunologically-Based Treatment of Cancers and Other Pathologies: (Specifics Later)

Cancer Antigens as

Targets for Therapy Radioactively-labeled Antibodies Cytolytic Antibodies Specifically Activated Antigen-presenting Cells.

Imaging with Antibodies Carrying “Reporter Groups”

Radioactive Isotopes Fluorescent Groups (“Chromophores”) Metals Antigen-Antibody Interactions in Research and Clinical Medicine e.g. Radioactively labeled monoclonal antibody reacting with tumor cell antigens in detection of metastatic colon cancer

Imaging on Metastatic Colon Carcinoma with Radioactive-Iodine-Labelled Monoclonal Ab to A33 Ag Lloyd Old, Scientific American, August, 1996, p. 138)

SeeMets Arm Head

Antihapten Antibodies in the Detection and Measurement of Small Molecules

For example: Anti-HCG (Human chorionic gonadotrophin) antibody in the detection of soluble HCG in urine

AntiHCG

What will happen when concentration of Anti-HCG-Ab is about equal to Hapten carrier conjugate?

What will happen when you put excess soluble hapten in the way of the anti-HCG-Ab?

PregTest

Antibodies in Blood Transfusions

Antibodies to A, B, O Blood Group Antigens Pre-existing Antibodies to Non-tolerated (Unmatched) Blood Group Antigens : “Isohemagglutinins”

ABOTypes

ABOAb

See Figure 15-13 (b), p. 389, Kuby, 6 th Edition

Not a hexasaccharide (No terminal sugar)

ABOSugar

See Figure 15-13 (a), p. 389, Kuby, 6 th

Galactose

Edition

Antibodies in Hemolytic Disease of the New-born (HNDB) (Rh-Factor Sensitization)

Rh-Factor positive baby – Rh Negative Mother

HDNB

See Figure 15-14 p. 390, Kuby 6 th Edition

HDNBPhoto

AntiRhAb

Following are three Turning Point short answer questions.

Please put all notes on the floor.

Do not have any electronic devices other than your NXT transmitter.

No consulting with other students.

If you have a problem with your device, I can provide you with a loaner NXT device. If you have a problem using your NXT device, please ask Elisabeth for help.

It is imperative that the integrity of these in-class Turning Point quizzes be maintained at the same level as we will do with the three written exams.

“Fill-in-the Blank” Question:

Hemolytic disease of the new-born is caused by maternal __ __ __ __ __ __ __ __ __ __ attacking the fetus in utero.

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“Fill-in-the Blank” Question:

RhoGam is an antibody that prevents sensitization of the Rh- mother by cells from her fetus. Why does that work?

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“Fill-in-the Blank” Question:

The antibody to Human Chorionic Gonadotrophin fails to cross link the HCG-hapten carrier conjugate and fails to make a precipitate if urine from a pregnant woman is added to the mixture. What is in the urine that is preventing the formation of the precipitate? Abbreviations are OK ______________________________________

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Immunopathology of Bacterial Septic Shock

Caused by Gram Negative Bacterial Endotoxins: Examples E. coli Pseudomonas aeruginosa Neisseria meningitidis Meningococcus 70,000 Deaths per year Diarrhea, Fever, Blood Clotting, Blood Pressure Drop Macrophage Activation by Endotoxin: Generates systemic cytokine production IL1 and TNF-alpha (Tumor necrosis factor) SepticShock

Immunopathology of Bacterial Toxic Shock

Exotoxins Secreted or Present Membrane Bound: Act as "Superantigens" Examples Staphylococcus aureus: TSST1 (Toxic Shock Syndrome Toxin) Streptococcus pyrogenes - Rheumatic fever and shock Staphylococcus enterotoxins: Food poisoning Superantigens cross-link TCR with Antigen-presenting Cell MHC Class II Proteins Generates systemic cytokine production - IL1 and TNF alpha (Tumor necrosis factor) ToxicShock

SuperAg

Staphylococcal enterotoxins (food poisoning) Streptococcal pyrogenes exotoxins (rheumatic fever, toxic shock) See Table 11-2, p. 367 See Figure 11-6 7 th Edition p. 367

Mitogens and Lectins Mitogens: Stimulate mitosis and cell division non-specifically (non-specific therefore stimulate polyclonally) Lectins: Proteins that bind to carbohydrate in glycoproteins (Can be potent mitogens) Glycoproteins: Conjugated protein with covalently attached carbohydrate residues

Examples of Mitogens Concanavalin A (Con A) : Non-specific T-cell mitogen Phytohemaglutinin (PHA): Non-specific T-cell mitogen Pokeweed Mitogen (PWM): Non-specific T- and B-cell Mitogen Lipopolysaccharide (LPS): Gram negative bacterial cell wall component Potent Polyclonal (non-specific) B-Cell Mitogen

Immune Adjuvants and the Immunogenicity of Vaccines (See Scientific American, October, 2009) Boosting Vaccine Power, pp 72 to 79 Activating Antigen-presentation by Cells of the Innate Natural Immune Response e.g. Purified derivatives of bacterial lipo-polysaccharides Bacterial DNA derivatives Bacterial flagellin protein

Specific Activation of Antigen-presenting Cells Extra-corporeally

(outside of the body)

Dendritic Cell Vaccines See Dendreon

Innate Natural Immunity and Systemic Sepsis: NOVA Video on Meningitis (Meningococcal Meningitis, Endotoxin, and Systemic Sepsis) http://www.pbs.org/wgbh/nova/meningitis/ Has video links to steps in meningococcal sepsis “Amy’s Story” and related NOVA Stories

tpfondy.mysite.syr.edu

The Story of the Oakwood Children See “Song of the Oakwood Children” as a self-running presentation

“Fill-in-the Blank” Question:

Human chorionic gonadotrophin (HCG) is a small peptide made immunogenic by being conjugated with a large molecular weight carrier molecule. Thus HCG is a special kind of antigen and is an example of a __ ___ ___ ___ ___ ___

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We watched the first part of a NOVA video called “Killer Disease on Campus”

What is the “Killer Disease”

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5 4 3 2 1 5. No problem. Please get moving!

4. Maybe a bit too fast, but mostly OK.

3. I’m following OK, I can catch up with what I miss.

4. I’m struggling to keep up. It’s too much too fast.

5. I’m lost (This slide is anonymous. I won’t know who you are) Duration: 0 Seconds

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Testing doing a “Fill-in-the Blank” Question:

Please send in your last name up to the first five letters:

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Fill-in-the Blank” Question:

A small organic molecule such as fluoro-dinitro benzene can be made immunogenic by attaching it to a

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