Antibodies, also known as immunoglobulins, are proteins produced by the immune system in response to foreign substances, such as viruses, bacteria, or other antigens. These proteins play a crucial role in the immune response, helping the body to recognize and neutralize foreign invaders.
Antibodies are Y-shaped molecules composed of four polypeptide chains: two identical heavy chains and two identical light chains. Each chain consists of a variable region (which determines antigen specificity) and a constant region (which defines the antibody’s class and mediates effector functions). The tips of the Y-shaped structure form the antigen-binding sites, which are unique to each antibody and can specifically recognize and bind to a particular epitope on an antigen.
There are five main classes of antibodies (IgA, IgD, IgE, IgG, and IgM), each with distinct functions and properties. Some of the primary roles of antibodies include:
- Neutralization: Antibodies can bind to and neutralize pathogens or toxins, preventing them from entering cells or exerting their harmful effects.
- Opsonization: Antibodies can coat the surface of pathogens, making it easier for phagocytic cells (like macrophages) to recognize and engulf them.
- Complement activation: Antibodies can trigger the complement system, a cascade of proteins that enhances the immune response by promoting inflammation, pathogen lysis, and phagocytosis.
- Antibody-dependent cell-mediated cytotoxicity (ADCC): Antibodies can recruit immune cells, such as natural killer (NK) cells, to destroy target cells by binding to both the antigen on the target cell and a receptor on the effector cell.
In addition to their natural role in the immune system, antibodies have become valuable tools in research, diagnostics, and therapeutics. Monoclonal antibodies, which are identical antibodies produced by a single B cell clone, have been developed as targeted treatments for a variety of diseases, including cancer, autoimmune disorders, and infectious diseases.
