IgG

Definition

IgG, or Immunoglobulin G, is the most abundant type of antibody found in the blood and extracellular fluid, playing a crucial role in the body's immune response against viruses. This antibody is essential for neutralizing pathogens, opsonization, and activating the complement system, making it vital for long-term immunity. IgG's ability to cross the placenta also provides passive immunity to the fetus, highlighting its importance in protecting newborns during early life.

5 Must Know Facts For Your Next Test

1. IgG constitutes about 75-80% of the total antibodies in serum, making it the most prevalent antibody type in the bloodstream.
2. It can bind to and neutralize a wide variety of pathogens including bacteria and viruses, making it essential for effective immune defense.
3. IgG is divided into four subclasses (IgG1, IgG2, IgG3, and IgG4), each with distinct functions and properties, tailored to different types of infections.
4. This antibody plays a significant role in the secondary immune response, being produced after re-exposure to an antigen for faster and stronger protection.
5. IgG's ability to cross the placenta allows it to provide passive immunity to infants during pregnancy, giving them protection against infections in their early months.

Review Questions

• How does IgG contribute to long-term immunity compared to other antibody types?
  • IgG is crucial for long-term immunity because it remains in circulation for extended periods after an initial exposure to an antigen. Unlike IgM, which is produced during the primary immune response, IgG is generated during the secondary response when the body encounters the same pathogen again. This allows for a quicker and more effective response due to its memory function, as well as higher affinity binding to the antigen compared to other antibodies.
• What role does IgG play in activating the complement system and enhancing pathogen clearance?
  • IgG can activate the complement system through its Fc region when it binds to antigens on pathogens. This activation leads to a cascade of reactions that enhance opsonization, where pathogens are marked for destruction by phagocytes. Additionally, complement activation can result in direct lysis of pathogens through the formation of membrane attack complexes, improving clearance from the body and contributing to a robust immune response against viral infections.
• Evaluate the significance of IgG's ability to cross the placenta and its implications for maternal-fetal immunity.
  • The ability of IgG to cross the placenta is significant as it allows for the transfer of maternal antibodies to the developing fetus, providing passive immunity during a critical period. This immunity helps protect infants from infections they might encounter in their early months before their own immune systems are fully developed. The presence of maternal IgG can be a lifesaver in preventing severe infections until the infant can mount its own immune responses through vaccination and exposure to pathogens post-birth.

Related terms

Antibody: A protein produced by B cells that binds specifically to antigens, helping to neutralize pathogens and mark them for destruction.

B Cells: A type of white blood cell that produces antibodies; they play a key role in the adaptive immune response.

Complement System: A group of proteins in the blood that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism.