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 immune response. It is primarily responsible for identifying and neutralizing pathogens like bacteria and viruses. IgG is unique among antibodies due to its ability to cross the placenta, providing passive immunity to the fetus, and its involvement in activating other immune components.

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 in circulation.
2. There are four subclasses of IgG (IgG1, IgG2, IgG3, and IgG4), each with slightly different roles in immune response.
3. IgG plays a vital role in opsonization, marking pathogens for destruction by phagocytes.
4. This antibody can activate the complement system, enhancing the ability to clear pathogens from the body.
5. IgG levels can be measured clinically to assess immune function or diagnose various diseases and infections.

Review Questions

• How does IgG contribute to the immune response against pathogens?
  • IgG contributes to the immune response by binding specifically to pathogens, marking them for destruction through processes like opsonization. When IgG binds to a pathogen, it can enhance phagocytosis by immune cells such as macrophages and neutrophils. Additionally, IgG can activate the complement system, leading to further recruitment of immune cells and lysis of the pathogen.
• Discuss the significance of IgG crossing the placenta and what implications this has for fetal immunity.
  • The ability of IgG to cross the placenta is significant because it provides passive immunity to the fetus during pregnancy. This transfer protects the unborn child from infections by allowing maternal antibodies to circulate in the fetal bloodstream. This maternal immunity is particularly crucial during the first few months of life before the infant's own immune system becomes fully functional.
• Evaluate the role of IgG subclasses in modulating immune responses and their clinical relevance.
  • The four subclasses of IgG (IgG1, IgG2, IgG3, and IgG4) play distinct roles in modulating immune responses based on their structure and function. For instance, IgG1 is particularly effective against protein antigens and can activate complement efficiently. Understanding these subclasses is clinically relevant because variations in their levels can indicate specific immune deficiencies or allergic responses, influencing treatment strategies for various diseases.

Related terms

Antibody: A protein produced by B cells that can specifically bind to antigens, helping to identify and neutralize foreign objects in the body.

Humoral Immunity: The aspect of immunity that involves the production of antibodies by B cells, which target pathogens in body fluids.

Plasma Cell: A type of white blood cell that produces large amounts of antibodies, including IgG, following activation by an antigen.