Module 5 Antigens

Antigens

are substances that are capable of stimulating an immune response. They activate lymphocytes, which are the body's infection-fighting white blood cells.

Vaccines

are intentionally administered antigens in an immunogenic form.

Vaccines

They are designed to induce a memory function in the adaptive immune system, allowing it to quickly recognize and respond to specific pathogens upon future exposure.

Foreign Antigens (Heteroantigens)

Origin: Originate from outside the body.

Foreign Antigens (Heteroantigens)

Examples:

Parts of or substances produced by viruses, bacteria, and protozoa.

Substances in snake venom.

Certain proteins in foods.

Components of serum and red blood cells from other individuals.

Allergens.

Proteins from transplanted tissues and organs.

Substances on the surface of foreign cells.

Toxins.

Other foreign particles.

Autoantigens (Self-Antigens)

Origin: Normally produced by the cells of the body ("self-protein"). They are special type of endogenous antigen

Autoantigens (Self-Antigens)

Mechanism: The immune system mistakenly identifies these antigens as foreign and attacks the body's own cells. This occurs in autoimmune diseases.

Autoantigens (Self-Antigens)

Examples: Nucleoproteins, nucleic acids.

Endogenous Antigens

Origin: Produced from within a normal cell and then presented outside of the cell on the cell surface.

Endogenous Antigens

Examples:

Antigens presented by cells infected by bacteria or viruses.

Blood group antigens on the surface of erythrocytes (red blood cells), such as the H antigen, A antigens, and B antigens.

HLA (Human Leukocyte Antigen) or histocompatibility leukocyte antigens.

Exogenous Antigens

Origin: Non-self antigens that are not cellular constituents of the body but have gained entry from the external environment (e.g., by inhalation or ingestion).

Exogenous Antigens

Mechanism: When recognized, they can be taken up by antigen-presenting cells (APCs) like macrophages and dendritic cells.

Exogenous Antigens

Examples: Allergens, proteins from transplanted tissues and organs, substances on the surface of foreign cells, toxins, and other foreign particles.

Proteins

Peptides (amino acid chains)

Polysaccharides (chains of monosaccharides/simple sugars)

Antigens are typically composed of:

Lipids and nucleic acids

generally become antigenic only when they are combined with proteins and polysaccharides.

Epitopes

Definition: Are the specific, immunologically active regions on an antigen that bind to antigen-specific membrane receptors on lymphocytes or to secreted antibodies.

Epitopes

Also known as: Antigenic determinants.

Epitopes

Significance: An antigen can have multiple epitopes, and different antibodies may bind to different epitopes on the same antigen.

Haptens

Definition: Are molecules with a low molecular weight, typically less than 10,000 Daltons.

Haptens

Antigenicity: Are usually not antigenic on their own. However, they can become antigenic when they are attached to a larger carrier molecule.

Complete Antigen

is a molecule that can elicit an immune response on its own and also contains epitopes.

Viral Antigens

are composed of:

Capsid: Made up of capsomers.

Nucleic acid: Genetic material (DNA or RNA).

Envelope: An outer membrane (not present in all virus species).

proteins in the capsid, envelope

The components of a virus, such as _____ or _____ , can act as antigens.

Red Blood Cells

have specific antigens on their surface that determine blood type. These antigens can elicit an immune response if transfused into an individual with different blood group antigens.

Group A Blood Antigen

Has A antigens on red blood cells and Anti-B antibodies in plasma.

Group B Blood Antigen

Has B antigens on red blood cells and Anti-A antibodies in plasma.

Group AB Blood Antigen

Has both A and B antigens on red blood cells and no antibodies in plasma.

Group O Blood Antigen

Has no A or B antigens on red blood cells and both Anti-A and Anti-B antibodies in plasma.