IgG
The most abundant in blood- Most abundant antibody in circulation
- Long-lasting protection
- Crosses the placenta (protects newborns)
- Important in responses to infections and vaccines
Immunoglobulins
The Body’s Targeted Defense
Antibodies recognize, neutralize and help eliminate threats.Immuno
What are Immunoglobulins ?
A family of antibodies with specialized functions.
Immuno
Structure of an antibody (Ig)
- 1Antigen-binding site
The tip binds a specific antigen.
- 2Variable region
Variable domains at the arm tips determine antigen specificity.
- 3Light chain
The shorter outer chain includes a variable domain and a constant domain.
- 4Heavy chain
The longer chain forms the inner arms and stem of the antibody.
- 5Constant region
Constant domains contribute to antibody class and function; the lower stem is the Fc region.
Antigen-binding site(recognizes a specific antigen)
Variable region(determines specificity)
Light chain
Heavy chain
Constant region(defines antibody class and function)
Key Functions
Neutralize pathogens and toxins
Mark targets for elimination
Activate the immune system (complement, Fc receptors)
Support lasting antibody protection
Maintain immune homeostasis
The Five Antibody Classes
Each immuno
IgM
The first responder- First antibody produced during a new infection
- Very effective at activating complement
- Often appears early in a response; persistence varies
- Secreted IgM is predominantly pentameric; membrane IgM is monomeric
IgA
Protection at body surfaces- Found in mucosal secretions (saliva, tears, gut, respiratory tract, breast milk)
- Helps prevent pathogen entry
- Exists as a dimer in secretions
- Important for mucosal immunity
IgE
Defense and allergy- Involved in defense against parasites (e.g. helminths)
- Binds to mast cells and basophils
- Mediates allergic reactions
- Present at low levels in blood
IgD
Still being discovered- Mainly found on the surface of naïve B cells
- May play a role in B-cell activation and regulation
- Present at very low levels in blood
- Functions are still under investigation
How Antibodies Work
Multiple mechanisms, working together.
Neutralization
Block viruses, bacteria or toxins from entering cells.
Opsonization
Coat pathogens to make them easier to engulf by immune cells (e.g. macrophages).
Complement activation
Trigger a cascade of proteins that help destroy pathogens.
Antibody-dependent cellular cytotoxicity (ADCC)
Recruit natural killer (NK) cells and other immune cells to eliminate infected or abnormal cells.
Antibodies and Vaccines
Vaccines train your immune system to make better antibodies.
B cells are activated
Plasma cells produce antibodies
Memory B cells provide long-term protection
Vaccines expose the immune system to antigens or instructions for producing an antigen, helping the body produce high-affinity antibodies and long-lived memory B cells. This prepares the immune system for a faster and stronger response upon future exposure.
Learn more about vaccinesAntibodies Change With Age
Aging can affect the quantity, quality and diversity of antibodies.
- Reduced B-cell diversity and function
- Lower responses to some vaccines
- Changes in class switching and affinity maturation
- Altered regulation of antibody-producing cells
- Greater variability between individuals
Key Takeaways
Antibodies are essential for a healthy, well-functioning immune system.
- Immuno
globulins are specialized proteins produced by B cells. - Each antibody class has unique functions and locations.
- Long-lived plasma cells sustain antibodies; memory B cells enable rapid recall.
- Vaccines stimulate the production of high-quality, long-lasting antibodies.
- Antibody responses can change with age, but remain modifiable.
Selected sources and references
Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.