IgG

Definition

IgG, or Immunoglobulin G, is the most abundant type of antibody in the bloodstream, playing a critical role in the immune response. It is known for its ability to neutralize toxins and pathogens, opsonize bacteria for easier phagocytosis, and activate complement pathways. IgG is a key player in forming a diverse range of antibodies and is involved in various immune interactions, highlighting its significance in immunity and disease processes.

5 Must Know Facts For Your Next Test

1. IgG is the only antibody class that can cross the placenta, providing passive immunity to the fetus during pregnancy.
2. There are four subclasses of IgG (IgG1, IgG2, IgG3, and IgG4), each with different functions and properties.
3. IgG has a high affinity for antigens due to affinity maturation, which enhances its effectiveness during subsequent exposures to the same pathogen.
4. Unlike other antibody classes, IgG can efficiently activate the complement system, leading to enhanced opsonization and lysis of pathogens.
5. IgG levels are commonly measured in clinical settings to assess immune function and diagnose various diseases.

Review Questions

• How does IgG contribute to antibody diversity and generation within the immune system?
  • IgG contributes to antibody diversity through the processes of somatic hypermutation and class switching. As B cells encounter antigens, they undergo these processes, allowing them to produce high-affinity IgG antibodies specific to those antigens. This means that over time, as B cells mature and proliferate, they generate a wide variety of IgG molecules that can recognize and neutralize a diverse range of pathogens effectively.
• What are the unique structural features of IgG that facilitate its function in immune responses?
  • IgG is structured with two heavy chains and two light chains forming a Y-shaped molecule, which allows it to bind specifically to antigens through its variable regions. The constant region of IgG interacts with other components of the immune system, such as complement proteins and Fc receptors on phagocytes. This structure not only enables effective binding but also ensures efficient signaling for immune responses like opsonization and activation of complement pathways.
• Evaluate the role of IgG in allergic responses and how it differs from IgE-mediated immunity.
  • While IgE is primarily associated with allergic responses by binding to allergens and triggering mast cell degranulation, IgG plays a more protective role against infections. In some cases, IgG can also bind allergens but typically does not induce an immediate hypersensitivity reaction like IgE does. Understanding this distinction highlights how IgG can help modulate immune responses without triggering excessive reactions, making it vital in maintaining balance within the immune system during allergenic challenges.

Related terms

Antibody: A protein produced by B cells that specifically binds to antigens, helping to neutralize or eliminate pathogens.

Class Switching:

The process by which a B cell changes the class of antibody it produces without altering the specificity for the antigen.

Opsonization:

The process by which antibodies tag pathogens for destruction by phagocytic cells, enhancing their clearance from the body.