Select the statements that accurately describe antigens. Antigens are molecules that trigger an immune response when recognized by the immune system. They can be exogenous, originating from outside the body, or endogenous, produced within the body. Antigens play a crucial role in the immune system’s ability to recognize and neutralize foreign invaders, such as bacteria, viruses, and toxins.

Antigens are highly diverse, varying in their chemical composition and structure. Some common types of antigens include proteins, carbohydrates, lipids, and nucleic acids. The immune system relies on specialized cells called antigen-presenting cells (APCs) to capture and display antigens to immune cells, such as T cells and B cells.

These immune cells recognize and bind to specific antigens, initiating an immune response tailored to eliminate the foreign invader.

Antigen Characteristics

Antigens are substances that trigger an immune response in the body. They are typically foreign substances, such as bacteria, viruses, or toxins, but can also be self-antigens, which are components of the body’s own cells.

Antigens are composed of a wide variety of molecules, including proteins, carbohydrates, lipids, and nucleic acids. The chemical composition of an antigen determines its specificity, which is the ability of the antigen to bind to a specific antibody or T cell receptor.

Types of Antigens

• Exogenous antigensare antigens that enter the body from outside sources, such as bacteria, viruses, or toxins.
• Endogenous antigensare antigens that are produced within the body, such as self-antigens or tumor antigens.

Examples of Antigens

• Bacteria: The lipopolysaccharide (LPS) component of bacterial cell walls is a common antigen.
• Viruses: The glycoproteins on the surface of viruses are antigens.
• Toxins: The exotoxins produced by bacteria are antigens.

Antigen Recognition

Antigen recognition is the process by which the immune system identifies and responds to antigens. The first step in antigen recognition is the capture and processing of antigens by antigen-presenting cells (APCs).

APCs are cells that express MHC molecules on their surface. MHC molecules are proteins that bind to peptides, which are short fragments of proteins. When an APC captures an antigen, it breaks it down into peptides and binds the peptides to its MHC molecules.

T Cell and B Cell Recognition

T cells and B cells are two types of lymphocytes that play a role in antigen recognition. T cells recognize antigens that are presented on MHC class I molecules, while B cells recognize antigens that are presented on MHC class II molecules.

When a T cell or B cell recognizes an antigen-MHC complex, it becomes activated. Activated T cells can kill infected cells or help B cells produce antibodies.

Antigen Specificity, Select the statements that accurately describe antigens

Antigen specificity is the ability of an antibody or T cell receptor to bind to a specific antigen. The specificity of an antibody or T cell receptor is determined by its variable region.

Antigen specificity is important in immune surveillance because it allows the immune system to distinguish between self and non-self antigens.

Antigen-Antibody Interactions

Antibodies are proteins that are produced by B cells in response to an antigen. Antibodies bind to antigens and neutralize them, preventing them from infecting cells.

There are different types of antibody-antigen interactions, including:

• Agglutination: Antibodies can cause antigens to clump together, making them easier for phagocytes to engulf.
• Precipitation: Antibodies can cause antigens to precipitate out of solution, forming a visible precipitate.
• Neutralization: Antibodies can bind to antigens and block their ability to infect cells.

Antibody-antigen interactions are used in a variety of diagnostic tests, such as the ELISA and Western blot.

Antigen Processing and Presentation

Antigen processing and presentation is the process by which APCs capture, break down, and present antigens to T cells and B cells.

The first step in antigen processing is the capture of antigens by APCs. APCs can capture antigens through a variety of mechanisms, including phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Once an APC has captured an antigen, it breaks it down into peptides and binds the peptides to its MHC molecules.

Role of MHC

MHC molecules are proteins that are expressed on the surface of all nucleated cells. MHC molecules bind to peptides and present them to T cells and B cells.

There are two types of MHC molecules: MHC class I and MHC class II.

• MHC class Imolecules are expressed on all nucleated cells. They present peptides to CD8+ T cells.
• MHC class IImolecules are expressed on APCs. They present peptides to CD4+ T cells.

Antigen processing and presentation is essential for the immune system to recognize and respond to antigens.

Antigen Tolerance

Antigen tolerance is the ability of the immune system to distinguish between self and non-self antigens. This is important to prevent the immune system from attacking the body’s own tissues.

There are two main mechanisms of antigen tolerance:

• Central toleranceoccurs in the thymus. During central tolerance, T cells that react to self-antigens are deleted.
• Peripheral toleranceoccurs in the periphery. During peripheral tolerance, T cells that react to self-antigens are suppressed or anergic.

Antigen tolerance is essential for the immune system to function properly. If antigen tolerance is broken, it can lead to autoimmune diseases.

Essential Questionnaire: Select The Statements That Accurately Describe Antigens

What are the characteristics of antigens?

Antigens are molecules that trigger an immune response when recognized by the immune system. They can be exogenous, originating from outside the body, or endogenous, produced within the body. Antigens vary widely in their chemical composition and structure, including proteins, carbohydrates, lipids, and nucleic acids.

How do antigens interact with the immune system?

Antigens are captured and displayed by antigen-presenting cells (APCs) to immune cells, such as T cells and B cells. These immune cells recognize and bind to specific antigens, initiating an immune response tailored to eliminate the foreign invader.

What is the role of antibodies in the immune response?

Antibodies are proteins produced by B cells that bind to specific antigens. They play a crucial role in neutralizing foreign invaders, such as bacteria and viruses, and facilitating their removal from the body.