Module 3 - Antigens and Antibodies

Antigen / Immunogen

Molecule that generates an immune response

Foreign molecular structures.

Antigenicity

Ability of a molecule to be recognized by an antibody or lymphocyte.

Gram negative organism

The cell wall of this is largely composed of peptidoglycan that is thin covered by an outer membrane consisting of lipopolysaccharides, Phospholipid and lipoprotein.

The lipopolysaccharide of these organism are mostly associated to its antigenicity.

Endotoxin

The bacterial lipopolysaccharides in gram negative bacteria are called?

exotoxins

Highly immunogenic proteins and stimulate the production of antibodies called antitoxins.

Toxoids

When exotoxins are treated with formaldehyde, it will lose its toxicity but retains its antigenicity and thus it will modified.

Lipopolysaccharide

Phospholipid

Lipoprotein

These are components of cell wall of gram negative bacteria

Viral antigens

can grow only inside living cells, thus, are “Obligate”, intracellular parasites.

Capsid proteins

good antigens and are highly capable of provoking an antibody formation.

Proteins in the virions

act as antigens and trigger an acquired immune response.

Fungi, protozoan parasites, helminths

These are other microbial antigens, which many different structures composed of proteins, carbohydrates, lipids and nucleic acid.

Non-microbial antigens

Some food may contain foreign molecules which may trigger an immune response and cause allergic reaction.

Inhaled dust can contain fungal spores or pollen grains and enter the respiratory system.

Good antigen

Large proteins, more complex carbohydrates, not readily degraded, structurally stable, and a Greater difference in structure to the animal’s own antigens.

Poor antigen

Smaller proteins, simple polysaccharides, Rapidly degraded, and have no fixed shape.

Epitopes or antigenic determinants

these are sites on an antigen’s surface that stimulate a specific immune response.

Haptens

Small molecule that cannot initiate an immune response unless it is bound to an immunogenic carrier molecule.

Carrier

The antigenic molecule to which the haptens attached.

Penicilloyl group

When penicillin is degraded in the body it forms.

Cross-reactivity

There are instances in which identical or similar epitopes can be found on apparently unrelated molecules.

The antibodies directed against one antigen may react unexpectedly with an unrelated antigen.

Antibodies directed against a protein in one species may also react in a detectable manner with a homologous or similar protein in another species.

Antibodies

Once a B cell responses is triggered, the receptors are shed into the surrounding fluid, where they act as antibodies.

Heavy and light chain

Antibodies consist of two pairs of proteins that are linked together by a disulfide bond.

Antibody function

Primary binds to antigen

Neutralize bacterial toxin

Prevent viral attachments to cells by forming a bridge between the phagocyte and invader.

Immunoglobulin G

Highest concentration in serum.

Made and secreted by plasma cells in the spleen, lymph nodes, and bone marrow.

Plays a major role in antibody-mediated defense mechanisms

Consists of two identical light chains and two gamma heavy chains.

This is the smallest antibody (which can escape from blood vessels more easily.

This is the Major antibody of the secondary immune response.

Immunoglobulin M

Produced by plasma cells in the spleen, lymph nodes and bone marrow.

Second highest concentration in the serum.

The Major antibody produced during a primary immune response although it is also produced during secondary immune response

IgM

Considerably more efficient than IgG at complement activation, opsonization, neutralization of viruses and agglutination

Due to very large size, they rarely enter tissue fluids at sites of inflammation

Immunoglobulin A

Secreted by plasma cells located under body surfaces (In the walls of intestine, respiratory tract, urinary system, skin and mammary gland)

This is considered the main antibody in the Mucosal surfaces of the body.

They either pass through epithelial cells into external secretions or diffuse into the bloodstream

IgA

Prevents antigens from adhering to body surfaces (important in protecting the intestinal, respiratory, and urogenital tracts, mammary glands and the eyes against microbial invasion.

Does not opsonize antigens and does not activate the classical complement pathway.

This is secreted in milk of lactating dams.

Immunoglobulin E

Produced beneath the body surfaces.

Typical Y-shaped, four-chain immunoglobulin with four constant domains in its heavy chains.

Low concentrations in serum.

It cannot simply bind and coat antigens but triggers acute inflammation by acting as a signal transducing molecule (signaling molecule) and are found on the surface of mast cell and basophil

It has the shortest shelf life (2-3 days)

This is an important immune response to parasites.

Immunoglobulin D

This is unique because it has not been detected in all mammals.

This is present in primates, rodents, cattle, sheep, pigs and dogs.

Absent in horses, rabbits and chickens.

This os present in trace amounts.

can be destroyed in mild treatment like IgE

Allotypes

The inherited sequence variations in heavy chain genes of the immunoglobulin.

The immunoglobulin of one individual may differ from that of another individual of the same species.

Idiotypes

Results from the variations in the amino acid sequences within the variable domains of light and heavy chains.

Differences associated with the antigen-binding region of an antibody

Monoclonal antibodies

Antibodies specific for one antigen

produce by hybridoma (cell line derived by the fusion of a single normal B cell and an immortal B cell tumor line)

This is widely use in research.

Polyclonal antibodies

A collection of antibodies from different B cells that recognize multiple epitopes on the same antigen

Affinity

A measure of the binding strength between an antigenic determinant (epitope) and an antibody binding site (paratope)

Avidity

The total strength of all the interactions in an antibody-antigen complex which may have more than on bonding sites

It is influenced by affinity as well as structural arrangements of epitope and variable regions of antibody.

Antigen binding site

Part of an antibody that binds antigen.

Anti-serum

Serum that contains a detectable number of antibody molecules that bind to a particular antigen.

Diversity

Presence of large numbers of antibodies that bind different specificities.

Domain

A region found in molecules coded for by members of the immunoglobulin supergene family, which comprises approximately 110 amino acids.

Fab (Fragment antigen binding)

Part of an antibody that contains the antigen-binding site of the molecule, composed of the variable regions of one light chain and one heavy chain.

Fc (Fragment crystallizable

Fragment of an antibody molecule lacking the antigen binding sites caused by papain digestion.

it contains the constant regions of both the heavy shains from the hinge region to the carboxyl terminus of the molecules

Paratope

Part of an antibody molecule that makes contact with the antigenic determinant.

Serum

Residual fluid when blood forms clot and is where antibodies can be found.