Antibodies: Definition, Types & Function

Overview

What are antibodies?

• Antibodies are proteins produced by the immune system to protect the body from foreign substances (antigens).
• Also known as immunoglobulins.

Antigen vs Antibody

• Antigens: Foreign substances like bacteria, viruses, fungi, allergens, and toxins.
• Antibodies: Proteins that attack and neutralize antigens.

How do antibodies work?

• Antibodies recognize antigens by their surface molecules.
• Produced by B cells (a type of white blood cell) upon contact with antigens.

Where are antibodies produced?

• Produced by B cells, which clone to release antibodies into the bloodstream and lymph system.
• Found in skin, lungs, tears, saliva, breast milk, and colostrum.

Monoclonal Antibodies

• Created in labs to mimic natural antibodies.
• Used in immunotherapy for fighting infections.

Function

Types of Antibodies

Antibodies are categorized into five classes, each with specific functions:

1. IgA

   • Location: Saliva, tears, mucus, breast milk, intestinal fluid.
   • Function: Protects against ingested and inhaled pathogens.

2. IgD

   • Location: Surface of B cells.
   • Function: Possible role in B cell maturation and activation.

3. IgE

   • Location: Skin, lungs, mucus membranes.
   • Function: Triggers allergic reactions through histamine release.

4. IgG

   • Location: Blood and tissue fluids.
   • Function: Protects against viral and bacterial infections.
   • Most common antibody type.

5. IgM

   • Location: Blood and lymph system.
   • Function: First line of defense; regulates immune response.

Anatomy

Structure of Antibodies

• Composed of proteins with four polypeptides (two heavy and two light chains).
• Y-shaped structure, differing in amino acid sequences.

Conditions and Disorders

Monoclonal Antibody Treatments

• Target specific antigens to treat various conditions:
  • Cancer
  • Rheumatoid arthritis
  • Heart disease
  • Multiple sclerosis
  • Ulcerative colitis
  • Lupus
  • Crohn's disease
  • Psoriasis
  • Organ transplant rejection

COVID-19 Antibodies

• Present in those recovered from COVID-19 or vaccinated.
• Antibody tests can determine presence.
• Duration: At least 5-6 months, potentially longer with memory B cells.

Thyroglobulin Antibodies

• Found in thyroid issues like hyperthyroidism and hypothyroidism.
• Test for thyroid problems or monitor post-cancer treatment.

Autoantibodies

• Also known as antinuclear antibodies (ANAs).
• Target normal proteins, potentially leading to autoimmune diseases.
• Tested via fluorescent antinuclear antibody test.

Conclusion

• Antibodies are crucial for immune defense against pathogens.
• Monoclonal antibodies are a therapeutic tool for a variety of diseases.

Note

• Seek advice from healthcare providers for more information on antibodies and related health conditions.

Cleveland Clinic Services

• Offers primary care, preventive screening, and specialized treatments.