Antigens: Types and Features

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Questions and Answers

What distinguishes superantigens from T-dependent antigens?

Superantigens activate specific lymphocytes only.

Superantigens cannot bind to T cell receptors.

Superantigens induce a monoclonal response.

Superantigens activate a large number of lymphocytes non-specifically. (correct)

What is the primary consequence of polyclonal activation by superantigens?

Increased production of monoclonal antibodies.

Enhanced production of immune suppressive factors.

Excessive release of pro-inflammatory cytokines. (correct)

Activation of B cells only.

What defines haptens in the context of immune response?

They are non-immunogenic but can activate immunity when conjugated to a carrier. (correct)

They are derived only from viruses.

They are fully immunogenic substances.

They can induce an immune response independently.

Which statement is true regarding autoantigens?

They are natural constituents of the body involved in autoimmunity. Signup and view all the answers

What characterizes exogenous antigens?

They originate from outside the body. Signup and view all the answers

Which age group typically has a better immune response to the same antigen?

Middle-aged individuals Signup and view all the answers

What type of antigens engage B lymphocytes without requiring helper T cells?

T-independent antigens Signup and view all the answers

Which of the following antigen types is predominantly formed by proteins?

T-dependent antigens Signup and view all the answers

What factor can enhance the body's immune response to an antigen?

Adjuvant Signup and view all the answers

Which of the following statements about nucleic acids as antigens is accurate?

Nucleic acids are generally weak antigens. Signup and view all the answers

Which antimicrobial route of administration is commonly used for most vaccines?

Intramuscular Signup and view all the answers

Which type of antigen is described as being resistant to degradation and having a polymeric structure?

T-independent antigens Signup and view all the answers

Which of the following is NOT a common route of vaccine administration?

Inhalation Signup and view all the answers

What are the two cardinal features of antigens?

Immunogenicity and antigenicity Signup and view all the answers

Which type of antigen is capable of stimulating an immune response on its own?

Immunogen Signup and view all the answers

What term refers to the specific part of an antigen responsible for inducing an immune response?

Antigenic determinant Signup and view all the answers

Which factor does NOT affect the immunogenicity of an antigen?

Lifespan of the host organism Signup and view all the answers

What type of antigens are produced by infectious agents like bacteria and viruses?

Microbial antigens Signup and view all the answers

Which type of antigen requires a carrier molecule to induce an immune response?

Hapten Signup and view all the answers

Which molecules are primarily involved in the binding of antigens?

Antibodies, MHC molecules, and lymphocyte receptors Signup and view all the answers

What characteristic of particulate antigens makes them more immunogenic compared to soluble antigens?

More efficient presentation by antigen-presenting cells Signup and view all the answers

What happens to antigens that are denatured compared to their native forms?

They are more immunogenic Signup and view all the answers

Which of the following is an example of a non-microbial antigen?

Tumor antigens Signup and view all the answers

Study Notes

Antigens

Antigens are molecules that trigger an immune response when introduced into the body.
They bind to antibodies, MHC molecules, or lymphocyte receptors (TCRs and BCRs).
There are two main types: immunogens and haptens.

Immunogens and Haptens

Immunogens: Substances that stimulate an immune response on their own.
Haptens: Substances that cannot induce an immune response by themselves but can do so when combined with a larger molecule, such as a host protein.

Cardinal Features of Antigens

Immunogenicity: The ability of an antigen to induce an immune response (T cells, B cells, antibodies).
Antigenicity: The ability of an antigen to bind to the products of the immune response it triggered (lymphocytes or antibodies).

Epitope or Antigenic Determinant

The specific part of an antigen responsible for inducing the immune response and binding to immune response products (lymphocyte receptors and antibodies).

Sources of Antigens

Infectious agents (microbial antigens): Bacteria, viruses, parasites, fungi.
Altered self-antigens: Tumor cells.

Challenges of Parasitic Antigens

Parasites often have complex life cycles, which can present challenges in developing effective vaccines.
Example: Malaria parasites have multiple stages in their life cycle, making it difficult to target a single antigen for vaccination.

Non-microbial Antigens

Cell Surface Antigens:
- Blood group antigens (A, B, AB, O)
- Rh Factor
- MHC class I (found on all nucleated cells)
- MHC class II (primarily found on antigen-presenting cells).

Factors Affecting Immunogenicity

Foreignness: The immune system primarily recognizes and targets non-self substances.
Size: Larger antigens tend to be more immunogenic.
Chemical composition: Complex molecules with diverse antigenic determinants are often more immunogenic.
Physical properties: Particulate antigens are generally more immunogenic than soluble antigens, and denatured antigens tend to be more immunogenic than native forms.
Degradability: Easily phagocytosed and degraded antigens are typically highly immunogenic.
Genetic factors: Variations in antigen receptor genes can influence an individual's immune response against a specific antigen.
Age: Young and elderly individuals may have a weaker immune response compared to middle-aged individuals.

Chemical Nature of Antigens

Proteins: The most common and potent antigens.
Polysaccharides: Can be strong immunogens.
Nucleic acids: Weak antigens, but can become highly immunogenic when combined with proteins.
Lipids: Generally not immunogenic, but some can act as haptens.

Routes of Administration (Vaccine Antigens)

Per os (oral): Polio vaccine
Intranasal: FluMist
Intramuscular: Most vaccines
Intravenous: Rarely used
Intradermal: BCG for tuberculosis vaccine
Subcutaneous: Most vaccines

Adjuvants

Substances that enhance the immune response to an antigen.

Types of Antigens

T-independent antigens: Directly stimulate B lymphocytes to produce antibodies without the need for helper T cells.
- Examples: Lipopolysaccharides
T-dependent antigens: Indirectly stimulate B lymphocytes to produce antibodies.
- Helper T cells are required.
- Examples: Proteins
Superantigens: Activate a large number of T cells non-specifically.
- Primarily derived from bacteria or viruses.
- Can lead to excessive cytokine production and systemic toxicity.
Haptens: Small, non-immunogenic substances that require conjugation to a carrier molecule to elicit an immune response.
Autoantigens: Self-antigens that the immune system normally does not recognize. They play a role in autoimmune diseases.
Exogenous antigens: Enter the body from external sources.
Endogenous antigens: Generated inside cells, often due to viral or bacterial infection.

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Description

This quiz covers the fundamentals of antigens, including their role in the immune response, types such as immunogens and haptens, and key concepts like immunogenicity and antigenicity. Test your understanding of how these molecules interact with the immune system and the importance of epitopes.