10. Antigens and Immunogens

What are the 5 types of antigens

• Proteins: best type of molecule that elicits a response

  • The bigger, more complex and more visible the better

• Polysaccharides: their repetitive structure elicits a response

  • Typically need to be bound to a protein

  • Typically T-cell independent B cell activation

• Nucleic acids: Fairl poor activators unless bound to proteins

  • Lupus is an example where patients produce antibodies against native dsDNA

• Lipids: Rarely elicit a response unless bound to protein or polysaccharide

  • LPS is one of the most potent stimulators of the immune system

• Superantigens: activate T cells regarding of specificity

  • Creates uncontrollable activation of T cells

  • Binds to MHC Class II outside of peptide groove

  • Binds to outer surface of TCR

  • Ex. Staph aureus

Antigen vs. Immunogen

• Antigen: Any molecules that can be bound by an antibody and or T cell

• Immunogen: an antigen that can elicit an immune response

• Anything can be an antigen but not all antigens are immunogens

What are Adjuvants?

What is the relationship in solution when adjuvants are added?

• Added to immunogenic antigens in order to maximize an immune response

  • Making the antigen bigger

  • Making antigen precipitate

• Adjuvants are added to a solution with Immunogen but they do not form stable linkages to each other

What are haptens?

What is one instance in which they CAN elicit an immune response?

• They are antigens that can be bound by antibodies, but do not elicit an immune response

• ANTIGENIC, NOT IMMUNOGENIC due to small size and simplicity

• They can elicit an immune response if bound to an immunogenic carrier protein

Explain the antibody production in relation to the following situations

• Hapten

• Carrier Immunogen

• Hapten + carrier

• Hapten → No antibodies

• Carrier immunogen → antibodies against carrier

• Hapten + Carrier → antibodies against Hapten, carrier AND hapten and carrier at the same time

Example of drug-induced haptenation

• IV Pen G acts as hapten and binds to RBC surface proteins (acts as carrier) and induces hemolytic anemia

• ______ molecular structures do not elicit much of an immune response

• Maximum stimulation occurs with ____ molecules because they are ___ soluble and more _____ for APCs to phagocytose

• _______ molecules are more easy to distinguish as foreign

• Homopolymers are ____ immunogens, while Heteropolymers are ___ immunogens

• Charge counts, charged molecules are ____ than uncharged neutral molecules

• HYdrophilic is ___ than hydrophobic

• Immunogens must be __________ so they can be processed and presented to T cells, this is why prosthetic devices are not immunogenic

• Small molecular structures do not elicit much of an immune response

• Maximum stimulation occurs with larger molecules because they are less soluble and more visible for APCs to phagocytose

• Complex molecules are more easy to distinguish as foreign

• Homopolymers are bad immunogens, while Heteropolymers are good immunogens

• Charge counts, charged molecules are better than uncharged neutral molecules

• Hydrophilic better than hydrophobic (bc we are hydrophobic)

• Immunogens must be degradable so they can be processed and presented to T cells, this is why prosthetic devices are not immunogenic

• The more ______, the more antibodies that can bind, the more immunogenic

• The more unlike ____ molecules, the better

• Dosage is important (goldilocks effect) because too low ____ ___ elicit a response and too high may elicit _____

• Route of administration determines which _____ and ______ will activate and ____ of antibody produced

• Some ______ defects confer non-responsiveness or decreased responsiveness

• Age also affects responsiveness as _____ have a still developing immune system and immunity ____ with age

• The more epitopes, the more antibodies that can bind, the more immunogenic

• The more unlike our molecules, the better

• Dosage is important (goldilocks effect) because too low will not elicit a response and too high may elicit anergy

• Route of administration determines which cells and organs will activate and isotype of antibody produced

• Some genetic defects confer non-responsiveness or decreased responsiveness

• Age also affects responsiveness as infants have a still developing immune system and immunity wanes with age

• BCR binds native molecules that are _______ around _____ of cells

• TCR binds to ____ that are presented on _____ complexes

• TCR and BCR can have the same _____ but not always the same _____

• BCR binds native molecules that are floating around outside of cells

• TCR binds to peptides that are presented on MHC complexes

• TCR and BCR can have the same antigen but not always the same epitope

Characteristics of BCR

• Binds proteins or peptides?

• Sequential or discontinuous binding?

• Epitope must be outside or inside?

• Recognizes what kinds of antigens?

• Binds anything, proteins, peptides

• Binding may be sequential or discontinuous

• Epitope must be on antigen external surface

• Recognizes nucleic acids, proteins, lipids and polysaccharides

Characteristics of TCR

• Binds proteins or peptides?

• Sequential or discontinuous binding?

• Epitope must be outside or inside?

• Recognizes what kinds of antigens?

• Binds peptides presented on MHC only

• Binding is sequential

• Epitope can be inside or outside, it doesn’t matter bc it will be broken down into peptides

• Recognizes almost always proteins