LECTURE 3: Antigens, Immunogens and Vaccines

ANTIGEN

Substance with the ability to combine or recognized with an antibody

IMMUNOGEN

Substance that is capable of inducing an immune response

False, not all antigens are strong enough to cause a full immune response.

TRUE OR FALSE:

All antigens are strong enough to cause a full immune response.

SPECIFIC REACTIVITY

Antigenicity is also known as?

ANTIGENICITY / SPECIFIC REACTIVITY

The ability of the antigen to react specifically with the antibodies or cells it provoked

IMMUNOGENICITY

The ability to provoke an immune response by stimulating the production of antibodies, proliferation of specific T cells, or both

• stimulating the production of antibodies

• proliferation of specific T cells

Immunogenicity is the ability to provoke an immune response by _____, _____, or both

immunogens

An immune response is triggered by ______.

TRUE

TRUE OR FALSE:

All immunogens are antigens but not all antigens are immunogens.

blood groups; red blood cells (RBCs)

Seen in the context of_____, where certain molecules on the surface of ____ act as antigens, but not all of them are strong enough to trigger an immune response.

ALL IMMUNOGENS ARE ANTIGENS BUT NOT ALL ANTIGENS ARE IMMUNOGENS

Blood group antigens; ABO system; Rh factor

______ like those in the _____ are strong immunogens, while some other antigens, like the ____, might not always cause a robust immune response in everyone.

ABO system

Example of strong immunogens

Rh factor

Example of weaker immunogens

immunogenic; antigenic

Foreign substances can be _______ or ______ if their membrane or molecular components contain structures recognized as foreign by the immune system.

FOREIGN SUBSTANCES

Can be immunogenic or antigenic if their membrane or molecular components contain structures recognized as foreign by the immune system.

TRUE

TRUE OR FALSE:

Not all surface act as antigenic determinants.

surface

Not all _____ act as antigenic determinants

Prominent

____ —> normally recognized by the immune system

EPITOPE

Part of an antigen that reacts specifically with an antibody or T-lymphocyte receptor.

antibody; T-lymphocyte receptor

Epitope is part of an antigen that reacts specifically with an ____ or ____.

EPITOPE

Precise molecular shapes or configurations recognized by B cells, or the peptide sequences detected by T cells.

B cells

Epitope are precise molecular shapes or configurations recognized by _____, or the peptide sequences detected by T cells.

T cells

Epitope are precise molecular shapes or configurations recognized by B cells, or the peptide sequences detected by ____.

EPITOPE

Known as the antigenic determinant.

ANTIGENIC DETERMINANT

Epitope are also known as the?

EPITOPE

Dictates the shape of the ANTIBODY

ANTIBODY

Epitope dictates the shape of the _____.

1. Linear Epitope

2. Conformational Epitope

TWO TYPES OF EPITOPE:

LINEAR EPITOPE

Sequential amino acids on a single polypeptide chain

(TWO TYPES OF EPITOPE)

CONFORMATIONAL EPITOPE

Folding of one or more polypeptide chains, bringing together amino acids that may be distant from each other.

1. Foreignness

2. Size

3. Chemical Composition and Complexity

4. Route, Dosage and Timing

5. Degradability

6. Adjuvants

FACTORS AFFECTING IMMUNOGENICITY:

FOREIGNNESS

↑ difference = ↑ immune response

FOREIGNNESS

Is the degree to which antigenic determinants are recognized as nonself by an individual’s immune system.

FOREIGNNESS

The immunogenicity of a molecule depends to a great extent on its degree of foreignness.

FOREIGNNESS

The immunogenicity of a molecule depends to a great extent on its degree of _____.

SIZE

↑ molecular weight = ↑ immune response

<5,000 daltons

______ can not trigger antibody production

(SIZE)

>10,000 daltons

Potential AG → MW: __________

(SIZE)

Potential AG

____ → MW: >10,000 daltons

(SIZE)

40,000 daltons (albumin)

Good Immunogen → MW: __________

(SIZE)

Good Immunogen

____ → MW: 40,000 daltons (albumin)

(SIZE)

albumin

An example of a good immunogen which has a MW of 40,000 daltons

(SIZE)

1 million daltons (hemocyanin)

Excellent Immunogen: MW: _______

(SIZE)

Excellent immunogen

_____ MW: 1 million daltons (hemocyanin)

(SIZE)

hemocyanin

An example of an excellent immunogen which has a MW of 1 million daltons

(SIZE)

SIZE

The number of antigenic determinants on a molecule is directly related to its ____.

PROTEINS

Example of effective antigens because of a large molecular weight.

(SIZE)

• Structural stability

• Complexity

CHEMICAL COMPOSITION, COMPLEXITY:

CHEMICAL COMPOSITION, COMPLEXITY

↑ Complexity = ↑ immune response

PROTEINS

Most immunogenic (heavy), ↑MW and structural complexity

(CHEMICAL COMPOSITION, COMPLEXITY)

POLYSACCHARIDE

Second; too small to function as antigen; rapidly degraded

(CHEMICAL COMPOSITION, COMPLEXITY)

LIPIDS

Least immunogenic; ↓ MW; ↓ stability; relatively simple

(CHEMICAL COMPOSITION, COMPLEXITY)

NUCLEIC ACID

Single stranded; can become immunogenic; molecular flexibility

(CHEMICAL COMPOSITION, COMPLEXITY)

STRUCTURAL STABILITY

If structure is not stable → poor antigen

• Totally inert molecules are poor antigen

(CHEMICAL COMPOSITION, COMPLEXITY)

STRUCTURAL STABILITY

Important in cases where the goal is to elicit a patient antibody response when administering a vaccine.

(CHEMICAL COMPOSITION, COMPLEXITY)

poor antigen

If structure is not stable → _______

(CHEMICAL COMPOSITION, COMPLEXITY)

COMPLEXITY

Complex proteins are better antigens than large repeating polymers such as lipids, carbohydrates, and nucleic acids

(CHEMICAL COMPOSITION, COMPLEXITY)

Complex proteins

____ are better antigens than large repeating polymers such as lipids, carbohydrates, and nucleic acids

(CHEMICAL COMPOSITION, COMPLEXITY)

ROUTE

This include intravenous (into a vein), intradermal (into the skin), subcutaneous (beneath the skin), intramuscular, and oral.

• intravenous (into a vein)

• intradermal (into the skin)

• subcutaneous (beneath the skin)

• intramuscular

• oral

Route includes:

ROUTE

Oral tolerance

• phenomenon where antigens delivered via the gastrointestinal tract are ignored by the cells of the adaptive immune system.

ORAL TOLERANCE

Phenomenon where antigens delivered via the gastrointestinal tract are ignored by the cells of the adaptive immune system

DOSAGE

_____ response may be partially dependent on the nature of immunogen processing

nature of immunogen processing

Dose response may be partially dependent on the _____

smaller

The (larger/smaller) the dose → less likely the response

OPTIMAL DOSE

• Too low → might not provide sufficient stimulus

OPTIMAL DOSE

• Too high → can lead to excessive inflammation or tolerance

Too low

_____ → might not provide sufficient stimulus

(OPTIMAL DOSE)

might not provide sufficient stimulus

Too low → ____

(OPTIMAL DOSE)

Too high

______ → can lead to excessive inflammation or tolerance

(OPTIMAL DOSE)

can lead to excessive inflammation or tolerance

Too high → _____

(OPTIMAL DOSE)

DOSE-RESPONSE RELATIONSHIP

As the dose of antigen increases, the immune response also increases up to a certain point.

increases

As the dose of antigen increases, the immune response also (increases/decreases) up to a certain point.

(DOSE-RESPONSE RELATIONSHIP)

DOSE-RESPONSE RELATIONSHIP

Beyond this point, the response might plateau or decline due to immune saturation or adverse effects.

plateau or decline

• As the dose of antigen increases, the immune response also increases up to a certain point.

• Beyond this point, the response might _____ due to immune saturation or adverse effects.

(DOSE-RESPONSE RELATIONSHIP)

immune saturation or adverse effects

Beyond this point (As the dose of antigen increases, the immune response also increases up to a certain point), the response might plateau or decline due to _____.

(DOSE-RESPONSE RELATIONSHIP)

TIMING

Primary and secondary responses

Primary immune response

Initial reaction to Ag + production of Ab and immune cells

(TIMING)

Secondary immune response

Re-exposure to the same Ag and is stronger and faster due to memory cells

(TIMING)

Proper timing

______ between doses, especially for booster shots, can enhance the strength and longevity of the immune response

(TIMING)

WINDOW OF OPPORTUNITY

Time when immune response is most effective

(TIMING)

WINDOW OF OPPORTUNITY

Administering booster doses or additional exposures within this window can maximize the immune response.

(TIMING)

DEGRADABILITY

The _____ of an immunogen refers to its ability to be broken down into smaller fragments that can be recognized and presented by cells of the immune system, primarily antigenpresenting cells (APCs).

DEGRADABILITY

These smaller fragments are then presented on the cell surface using major histocompatibility complex (MHC) molecules to activate T cells and initiate an immune response.

ANTIGENPRESENTING CELLS (APCs)

The degradability of an immunogen refers to its ability to be broken down into smaller fragments that can be recognized and presented by cells of the immune system, primarily _____.

major histocompatibility complex (MHC)

These smaller fragments are then presented on the cell surface using ________ molecules to activate T cells and initiate an immune response.

(DEGRADABILITY)

activate T cells and initiate an immune response

These smaller fragments are then presented on the cell surface using major histocompatibility complex (MHC) molecules to ________.

(DEGRADABILITY)

DEGRADABILITY

Failure will lead to defective immune response

• Chediak Higashi Syndrome

(DEGRADABILITY)

Chediak Higashi Syndrome

Failure will lead to defective immune response

• _______

(DEGRADABILITY)

ADJUVANTS

Known as antigen delivery systems / immunopotentiators

• antigen delivery systems

• immunopotentiators

Adjuvants are also known as?

ADJUVANTS

Are substances added to vaccines to enhance/boost the body’s immune response to the vaccine antigen.

vaccines

Adjuvants are substances added to _____to enhance/boost the body’s immune response to the ____ antigen.

ADJUVANTS

Stimulate T, B and phagocytic cells

T, B and phagocytic cells

Adjuvants stimulate what cells?

ADJUVANTS

They are especially important when the antigen itself is weakly immunogenic (doesn’t trigger a strong immune response).

weakly immunogenic

They are especially important when the antigen itself is ________.

(ADJUVANTS)

• Antigen presentation

• Inflammation and cytokine release

• Enhanced T cell activation

• Memory cell formation

• Stimulation of innate immunity

How adjuvants enhance the immune response:

• Aluminum Salts

• Oil-in-water emulsions

• Microparticles

EXAMPLES OF ADJUVANTS:

Aluminum Salts

Most commonly used adjuvants in vaccine