Lecture 6:Antibodies Flashcards
Immunoglobulins are
Immunoglobulins are also called antibodies
Part of the humoral immune system
Antibodies are produced by
Produced by plasma cells
Derived from B cells.
Different types with different purposes
Importance of antibodies
Host defense (binding and neutralization)
Vaccination
Testing
Antibodies are used for diagnostics how
Used diagnostically to detect infections
Rising titers
Means higher serum antibody levels.
Recent infection
Antibodies are used for
Used to fight infections.
Vaccines boost antibody titers – often the basis for judging their effectiveness.
Hyperimmune sera may be prescribed to treat infections
Basic immunoglobin structure
All immunoglobulin molecules have the same basic flexible Y shape with a hinge region.
The stalk/tail of Y is the crystallizable fragment (Fc)
Top of Y is two antigen binding fragments (Fab)
The stalk of immunoglobulin does
Constant within an antibody class
Determines class of immunoglobulin
Responsible for effects of the Ig when the head binds an antigen.
Top of the Y in immunoglobulin is
Composed of both constant and variable regions
A given clone of plasma cells (daughters of a common B cell) produce an Ig that is specific for one particular antigen
Fc mediates binding to
Host tissue
Various cells of the immune system
First component of complement system
Fab binds antigen for
Marks antigen for immunological attack
Activates nonspecific defense mechanisms that can destroy antigen
e.g., opsonization for enhanced phagocytosis
Site of production of immunoglobulin
Ig are produced by B Cells and Plasma Cells
B cells put Ig on their surface
Plasma cells excrete Ig into the body fluids
Lymph- drains into vascular system
Four types of immunoglobulin
IgM
IgG
IgE
IgA
Each type can bind to the same antigen (Ag)
The distribution of antibody and the effects of binding vary with the type.
IgM come from and goes to
All B cells initially produce IgM
Then gradually switch to produce one of:
IgG
IgA
IgE
IgM looks like
IgM looks like 5 Ig molecules joined together.
IgM is a big molecule so is mainly restricted to blood
Lots of binding sites (each one is weak)
IgM does what
Protective actions
Efficient at agglutination (binding antigen together)
May precipitate antigens.
Functions of IgM
Neutralization
Complement activation
How does IgM neutralize
Binds to antigen making them ineffective
Pathogenic bacteria often have specialized structures so that they can attach to host cells.
Blocked by antibody.
How is IgM part of complement activation
Classical pathway
Results in:
Inflammation (attractants for nutrophils)
Opsonization
Membrane attack complex
IgG is produced when
As the immune response matures and becomes more efficient:
B cells switch from producing IgM to other Ig including IgG
In consequence, so do their plasma cells.
The major antibody of serum
Smaller than IgM so can reach sites of inflammation more easily
IgG is the principal antibody of tissue fluids.
Several sub-classes
Function of IgG
Antibody defense
Agglutination of antigens
Neutralization
Complement activation
Opsonisation by direct binding
Antibody-dependent cell-mediated cytotoxicity
How does IgG neutralize things
Binds much more tightly than IgM.
Blocks adhesion sites on pathogens
Bind and block toxins
How does IgG do complement activation
Classical pathway.
Requires 2 IgG molecules to be bound close together
How does IgG do opsonisation
Ig head binds to antigens e.g. on surface of bacteria
Ig tail changes shape
Can now bind to phagocytes.
Phagocytes engulf the antigen (e.g. bacteria) that the IgG is attached to
Antibody dependent cell mediated cytotoxicity is done by IgG by
Some pathogens are just too big to be engulfed
Cells infected with virus.
Instead, antigen-IgG complexes bind to NK cells.
NK cell kills infected cell
Antigen-antibody complexes may also bind to neutrophils and eosinophils and stimulate them to release oxidants.
Veterinary application of immunoglobulin
Serial measurements of Ig to determine if a pathogen is the underlying cause of clinical signs in the patient:
Serial Ig measurements
IgM will increase with acute infection, not if historically infected
IgG will increase during acute infection.
Titer testing for importation of animals- rabies
IgA is and secreted by
IgA is the major antibody of mucosal surfaces ex. Gut, respiratory tract
Gut lymphoid tissue is a major site of IgA production.
Secreted as a dimer with secretory piece.
Transport tag for epithelial cells.
Confers resistance to digestive enzyme
IgA works by
Works by neutralization
Viruses
Prevents microbes from binding to body surfaces
Agglutination
IgA cannot activate phagocytes (opsonize), does not bind complement.
How much IgA is produced and where is it located
More Ig A produced in a day than all others combined.
Only a small amount in serum
IgE is produced in
Produced by plasma cells just below body surfaces
IgE works by
Most binds to surface of basophils and mast cells in tissues before it binds to antigen.
IgE is the sentinel antibody
Antigen binding causes release of granules
Triggers acute inflammation
Important in parasite defense
Important in allergies
Immediate hypersensitivity
Free IgG is
Small amounts
Head of IgE binds to pathogens.
Parasites
Tail of IgE-Ag complex attracts and binds eosinophils.
Release enzymes that digest parasite
Another example of antibody dependent cell cytotoxicity
IgD is present in
Present in some, but not all domestic animals
Largely attached to B cells
Significant variations in structure between species
Function of IgD
Function unknown
Suspected of aiding in regulation of B cell response.
