IgG

Definition

IgG, or Immunoglobulin G, is the most abundant type of antibody found in the human body. It is a critical component of the adaptive immune system, responsible for recognizing and neutralizing foreign pathogens, toxins, and infected cells to protect the body from disease.

5 Must Know Facts For Your Next Test

1. IgG is the most prevalent antibody isotype in the blood and extracellular fluid, accounting for approximately 75-80% of total antibody levels.
2. IgG is highly versatile, able to neutralize toxins, activate the complement system, and tag pathogens for phagocytosis by other immune cells.
3. IgG is the only antibody class that can cross the placenta, providing passive immunity to the developing fetus.
4. There are four subclasses of IgG (IgG1, IgG2, IgG3, IgG4) that have slightly different structures and functions.
5. IgG levels can be used as a diagnostic marker to assess immune system function and identify conditions like immunodeficiencies or autoimmune disorders.

Review Questions

• Explain the role of IgG in the adaptive immune response.
  • IgG plays a central role in the adaptive immune response by recognizing and binding to specific antigens, marking them for destruction or neutralization. IgG can neutralize toxins, activate the complement system to lyse pathogens, and tag microbes for phagocytosis by other immune cells. This versatility makes IgG a critical component of the body's defense against a wide range of foreign invaders and infected cells.
• Describe the significance of IgG's ability to cross the placenta.
  • The ability of IgG to cross the placental barrier is particularly important, as it allows for the passive transfer of maternal antibodies to the developing fetus. This provides the newborn with immediate protection against pathogens, as the infant's own immune system is still maturing. The transfer of IgG antibodies from mother to child helps to bridge the gap until the infant's adaptive immune system can fully develop and generate its own specific antibodies.
• Analyze how differences in IgG subclasses can impact their functional capabilities.
  • The four IgG subclasses (IgG1, IgG2, IgG3, IgG4) have slightly different structures and, as a result, exhibit distinct functional properties. For example, IgG1 and IgG3 are more effective at activating the complement system and promoting phagocytosis, while IgG4 is less inflammatory and may play a role in dampening immune responses. These subclass-specific differences allow the adaptive immune system to mount tailored responses to different types of pathogens and threats, highlighting the versatility and complexity of the IgG antibody class.

Related terms

Antibody: A protein produced by plasma B cells that recognizes and binds to specific antigens, marking them for destruction or neutralization by the immune system.

Adaptive Immune System: The part of the immune system that learns to recognize and respond to specific threats, developing targeted and long-lasting immunity.

Antigen: A molecule or substance that the immune system recognizes as foreign and potentially harmful, triggering an immune response.