Antigen Part I

Immunogenicity: The capacity of antigens to generate

an immunological response

Foreignness: Antigens usually contain molecules or

substances that aren't usually found in the host organism.

Antigenic determinants (epitopes): interact with

antigen-specific receptors on immune cells

Diversity: The chemical makeup, origin, and structure of

antigens vary greatly.

Self- awareness: Differentiate between non-self

antigens obtained from outside invaders and self-

antigens, which are parts of the host organism's own

cells and tissues.

Processing and Presentation of Antigens: Specialized

antigen-presenting cells (APCs), such as dendritic cells,

macrophages, and B cells, process and present antigens

to immune cells.

Immunological memory : ability of the immune system

to remember previous interactions with particular

antigens as a result of exposure to those antigens.

✓ Bacterial

✓ Viral

✓ Fungal

✓ Parasitic

✓ Food

✓ Dust

✓ Pollen grains

✓ Snake/Mosquite bite

Most of the antigenicity of gram- negative bacteria

is associate with the lipopolysaccharide.

consist of an oligosaccharide attached to a lipid

(lipid A) and to a series of repeating trisaccharides-

determines the antigenicity of the organism.

Genus Salmonella – 250 serovars based on

antigenicity.

Polysaccharide antigens – O antigens

Bind to TLRs and PRRS

Example of endotoxins

Capsule / K antigens- protect bacteria against

phagocytosis and intracellular destruction

Short projections

Role in bacterial conjugation and movement

Contains flagellin

Used for bacterial movement

Porins – proteins that form pores on the surface of gram-negative organisms.

Heat shock proteins – large amount in stressed bacteria. Response to stressful conditions

(temperature, toxins and infections).

Exotoxins- highly immunogenic proteins and stimulate the production of antibodies called

antitoxins.

Bacterial nuclei acid rich in unmethylated CpG dinucleotides serve both as effective antigens for

adaptive and innate immunity.

Capsid consist of multiple capsomeres– good

antigen and capable of stimulating antibody

responses.

Envelope containing lipoproteins and

glycoproteins.

Gene code for new proteins- some are expressed

on the surface of infected cells.

Synthesized inside an animal’s own cells can still

bind to antigen receptors and provoke adaptive

immunity. – Endogenous antigens.

Synthesized inside an animal’s own cells can still

bind to antigen receptors and provoke adaptive

immunity. – Endogenous antigens.

Food contain many foreign molecules

Inhaled dusts can contain antigenic particles such as pollen grains

Organ grafts are foreign to animal

Outer membrane of every mammalian cell consists of a fluid lipid bilayer with a

complex mixture of protein molecules embedded to it.

Glycoprotein known as blood group antigens are found on the surface of RBCs.

Nucleated cells such as leukocytes possess hundreds of different protein molecules on

their surface.

The cell surface proteins that trigger graft rejection are called histocompatibility

antigens

Autoimmune response- an animal may mount immune responses against normal body

components.

Autoantigens- induces autoimmune response.

Hormones such as thyroglobulin

Structural component such as basement membrane

Complex lipid (myelin)

Intracellular components (mitochondrial components, nucleic acid, or nucleoproteins).

Cell surface proteins such as hormone receptors

size , stability , complexity, foreigness

what makes a good antigen

Ability of the molecules to be antigen.

Varies from one molecule to another.

Influenced by factors such as stability, route of administration,

antigens due to rapid degradation.

Foreign proteins especially large ones (1000 Da).

Large proteins; antigens of microorganisms

clostridial toxin, bacterial flagella, virus capsids, protozoan cell

membranes.

Snake venoms, serum proteins, cell surface proteins, milk and food

proteins, hormones, antibody molecules.

More complex carbohydrates may be

effective especially if bound to proteins.

Mammalian nucleic acids – relative

simplicity and flexibility, vert rapidly

degraded.

Proteins- most effective antigens

Complex bacterial lipopolysaccharide

Complex proteins- many different amino

acids

Structural stability

Simple polysaccharides (starch and glycogen)-

easy degradation

Lipids – wide distribution, relative simplicity,

structural instability and rapid metabolism.

Starch and other simple repeating polymers

Highly flexible molecules that have no fixed

shape

Immune responses are antigen driven, foreign

molecules that are unstable and destroyed very rapidly may not persist for a

sufficient time to stimulate an immune response