Classes of Antibodies:
There are five main classes of antibodies (also known as immunoglobulins), each with distinct characteristics and functions:
1. IgG (Immunoglobulin G):
- Most abundant: Makes up about 70-80% of all antibodies in the bloodstream.
- Long half-life:
Can circulate in the blood for weeks or months, providing long-term immunity.
- Neutralizes pathogens:
Can directly bind to and neutralize viruses and bacteria.
- Activates complement system:
Triggers a cascade of immune proteins that further attack and destroy pathogens.
- Crosses placenta:
Can provide passive immunity to a developing fetus.
2. IgM (Immunoglobulin M):
- First-line defense:
First antibody produced in response to a new infection, offering immediate but short-lived immunity.
- Large molecule:
Efficiently binds to pathogens but cannot easily enter tissues.
- Agglutination:
Causes pathogens to clump together, making them easier for phagocytes to engulf.
3. IgA (Immunoglobulin A):
- Present in mucosal secretions:
Found in tears, saliva, breast milk, and respiratory and gastrointestinal secretions, providing protection against mucosal infections.
- Neutralizes toxins and viruses:
Prevents them from attaching to mucosal surfaces.
- Dimers and monomers:
Exists in two forms, monomers for mucosal secretions and dimers for blood circulation.
4. IgD (Immunoglobulin D):
- Least abundant:
Makes up less than 1% of antibodies.
- Role unclear:
Its exact function is not fully understood, but it may be involved in B cell activation and immune memory.
5. IgE (Immunoglobulin E):
- Mediates allergic reactions:
Binds to mast cells and basophils, triggering the release of histamine and other inflammatory chemicals that cause allergic symptoms.
- Defense against parasites:
Also plays a role in defense against certain parasites.
Understanding the different classes of antibodies helps us appreciate the diverse ways our immune system protects us from various types of threats.
