IgG, or Immunoglobulin G, is a type of antibody and is the most common antibody found in human blood and other body fluids, representing about 75% of the antibodies in human serum. It plays a crucial role in the body's immune response by identifying and neutralizing pathogens like bacteria, viruses, and fungi. IgG is produced by plasma B cells as part of the secondary immune response, meaning it is generated after the initial infection or vaccination to provide longer-term immunity. It is the only antibody type that can cross the placenta from mother to fetus, providing the newborn with protection during the first months of life. Functions of IgG include:
- Binding to pathogens to immobilize and clump them together (agglutination)
- Coating pathogens (opsonization) to enable immune cells to recognize and destroy them
- Activating the complement system, which helps eliminate pathogens
- Neutralizing toxins
- Participating in antibody-dependent cell-mediated cytotoxicity and other immune functions
IgG antibodies are small enough to diffuse easily into tissues and are the primary antibody used in clinical diagnostics and immunological research due to their abundance and specificity. Detection of IgG often indicates prior infection or successful vaccination. There are four subclasses of IgG, each with slightly different roles in the immune system. IgG contributes significantly to long-term immunity and immune memory, helping the body respond faster upon re-exposure to the same pathogen. In summary, IgG is the predominant antibody in blood and a key player in protecting the body from infections, as well as in providing newborns with passive immunity from the mother.
