IgG

Definition

IgG, or Immunoglobulin G, is the most abundant type of antibody found in the human body. It plays a crucial role in the adaptive immune response, contributing to pathogen recognition, phagocytosis, and the regulation of humoral immunity.

5 Must Know Facts For Your Next Test

1. IgG is the most prevalent antibody in the blood and extracellular fluid, accounting for approximately 75-80% of total antibody content.
2. IgG is the only antibody class that can cross the placenta, providing passive immunity to the fetus during pregnancy.
3. IgG plays a crucial role in the secondary immune response, as it is produced in large quantities upon re-exposure to a pathogen.
4. IgG can activate the complement system, a cascade of proteins that aids in the destruction of pathogens.
5. IgG can bind to Fc receptors on phagocytic cells, such as macrophages and neutrophils, to facilitate the clearance of pathogens.

Review Questions

• Explain the role of IgG in pathogen recognition and phagocytosis.
  • IgG antibodies bind to specific antigens on the surface of pathogens, marking them for destruction. This process is known as opsonization. The Fc region of the IgG molecule can then interact with Fc receptors on phagocytic cells, such as macrophages and neutrophils, triggering the engulfment and digestion of the pathogen through the process of phagocytosis. This enhances the efficiency of the immune response by facilitating the clearance of invading microorganisms.
• Describe how IgG contributes to the regulation of humoral immunity.
  • IgG plays a crucial role in the regulation of humoral immunity, which involves the production of antibodies by B cells. Upon exposure to a pathogen, B cells differentiate into plasma cells that secrete IgG antibodies. These IgG antibodies can then bind to the same pathogen, neutralizing it or marking it for destruction by other immune cells. Additionally, IgG can provide feedback inhibition to B cells, regulating the production of antibodies and preventing an excessive immune response.
• Analyze the significance of IgG in the context of hypersensitivity reactions.
  • IgG antibodies can contribute to the development of certain types of hypersensitivity reactions, such as type II and type III hypersensitivities. In type II hypersensitivity, IgG antibodies bind to self-antigens or foreign antigens on the surface of cells, leading to their destruction. In type III hypersensitivity, IgG antibodies form immune complexes with antigens, which can deposit in tissues and trigger an inflammatory response. Understanding the role of IgG in these hypersensitivity reactions is crucial for the diagnosis and management of autoimmune disorders and other immune-mediated diseases.

Related terms

Antibody: A protein produced by B cells that binds to specific antigens, marking them for destruction or neutralization.

Phagocytosis: The process by which a cell engulfs and digests foreign particles, pathogens, or dead cells.

Humoral Immunity: The branch of the adaptive immune system that involves the production of antibodies by B cells to neutralize or destroy pathogens.