OIA1010 ANTIGEN & IMMUNOGENECITY

What is the primary function of the immune system?

To recognize and eliminate invaders while discriminating between foreign and self.

What is an antigen?

A molecule, often a protein or polysaccharide, capable of generating an immune response by being recognized by B or T cells.

Define immunogenicity.

The ability of a substance (immunogen) to provoke a specific immune respons.

What is the difference between antigenicity and immunogenicity?

Antigenicity is the ability to bind components of the immune system, while immunogenicity is the ability to provoke an immune response.

What are epitopes?

Antigenic determinants, or the specific parts of an antigen that bind to antibodies or T-cell receptors.

What are haptens?

Small molecules that become immunogenic only when conjugated to a carrier.

What are the four characteristics required for immunogenicity?

Foreignness, high molecular weight, chemical complexity, and degradability.

Why are high molecular weight substances more immunogenic?

Larger molecules provide more structural variety for immune recognition, e.g., proteins > 6,000 Da are generally immunogenic.

How does chemical complexity affect immunogenicity?

More complex molecules (with varied chemical moieties) are better recognized and elicit stronger immune responses.

What are the two main types of immune responses?

Humoral (antibody-mediated) and cellular (T-cell-mediated) immune responses.

What role do plasma cells play in immunity?

They produce antibodies that neutralize antigens and attract phagocytes.

How do cytotoxic T cells (Tc) kill infected cells?

By releasing toxins that induce lysis or apoptosis in cells presenting antigens on Class I MHC molecules.

What are the three classifications of antigens based on origin?

Exogenous (outside the body), endogenous (inside the cell), and autoantigens (self-antigens).

What are tolerogens?

Antigens that induce immune non-responsiveness (tolerance), potentially becoming immunogenic if their molecular form changes.

What are allergens?

Specialized immunogens that induce hypersensitivity reactions (e.g., pollen, food molecules).

What is autoimmunity?

An aberrant immune response where the body attacks its own tissues, leading to diseases like systemic lupus erythematosus (SLE).

What is immunological tolerance?

The immune system's unresponsiveness to self-antigens or manipulated tolerance for external antigens (e.g., organ transplantation).

What is the role of antigen-presenting cells (APCs)?

To process antigens and present them to T cells using MHC molecules.

Differentiate between Class I and Class II MHC molecules.

Class I presents endogenous antigens to CD8+ T cells; Class II presents exogenous antigens to CD4+ T helper cells.

How do macrophages assist in antigen presentation?

By phagocytizing pathogens, breaking them down, and presenting fragments on Class II MHC molecules.

What are Th cells and their function?

Helper T cells (CD4+) activate and direct other immune cells, aiding in antibody class switching and cytotoxic T cell activation.

What are Tc cells?

Cytotoxic T cells (CD8+) that kill virus-infected or tumor cells.

How does HIV affect the immune system?

It infects and depletes CD4+ T helper cells, leading to immunodeficiency (AIDS).

Give an example of an immunogen and a hapten.

Immunogen: tetanus toxin; Hapten: penicillin when conjugated with proteins.

What is an example of an exogenous antigen?

Pollen or bacteria ingested by phagocytes.

Name an autoimmune disease involving autoantigens.

Rheumatoid arthritis (RA), where self-proteins are targeted by the immune system.

Compare humoral and cellular immune responses.

Humoral uses antibodies to neutralize pathogens; cellular targets infected cells through Tc cells.

How do endogenous and exogenous pathways differ?

Endogenous involves intracellular antigens (Class I MHC); Exogenous involves extracellular antigens (Class II MHC).

What is the distinction between immunogens and tolerogens?

Immunogens stimulate immune responses, while tolerogens induce non-responsiveness.

What structural features of proteins can antibodies recognize?

Primary (amino acid sequence), secondary (α-helix, β-sheet), and tertiary (3D configuration) structures.