1. Definition
An antibody, or immunoglobulin (Ig), is a Y-shaped glycoprotein produced by B-cells in response to the presence of foreign molecules called antigens. Antibodies specifically bind to these antigens to neutralize them or mark them for elimination by other immune cells.
2. Structure
Each antibody consists of
- Two heavy chains and two light chains linked by disulfide bonds.
- The variable region at the tips of the Y-arms binds specifically to antigens, giving the antibody its unique specificity.
- The constant region determines the class of the antibody and its interactions with other components of the immune system (e.g., macrophages, complement proteins).
This Y-shaped structure allows antibodies to simultaneously bind antigens and recruit other immune system components to eliminate the pathogen.
3. Classification (Isotypes)
There are five primary antibody isotypes, each with a different role in immunity:
4. Role
Antibodies are critical to the adaptive immune system, which provides long-term, specific immunity against pathogens. They serve several functions:
- Neutralization: Antibodies can block the harmful effects of pathogens by binding to their surface antigens, preventing them from infecting cells.
- Opsonization: By coating pathogens, antibodies make them more recognizable to phagocytic cells (such as macrophages), thereby enhancing their elimination.
- Complement activation: Certain antibodies trigger the complement cascade, leading to pathogen lysis (destruction).
5. Therapeutic applications
Monoclonal antibodies (mAbs) are laboratory-made antibodies designed to target specific antigens with high precision. They have revolutionized the treatment of several diseases, including:
- Cancer: Monoclonal antibodies can target cancer cells by blocking growth signals or delivering cytotoxic agents directly to the tumor.
- Autoimmune diseases: In diseases such as rheumatoid arthritis and lupus, antibodies are used to inhibit specific immune pathways that cause inflammation and tissue damage.
- Infectious diseases: Antibodies neutralize pathogens such as viruses (e.g., COVID-19) by binding to their surface proteins, preventing them from infecting host cells.