I G

Immunoglobulin G (IgG) is a type of antibody that plays a critical role in the immune system's ability to fight off infections and diseases. It is the most abundant type of antibody found in human blood and extracellular fluid, allowing it to control infection of body tissues. By recognizing and binding to specific antigens, such as bacteria and viruses, IgG can neutralize their pathogenic effect. This article provides an overview of the structure, function, and clinical significance of IgG.

Structure

Immunoglobulin G is a glycoprotein molecule that consists of two identical heavy chains and two identical light chains, linked by disulfide bonds, forming a Y-shaped structure. Each IgG molecule has two antigen-binding sites, which are specific to the antigen it targets. The variability of these sites allows for the immune system to recognize an extensive range of antigens.

Function

The primary function of IgG is to protect the body against bacterial and viral infections. IgG antibodies can neutralize toxins, opsonize pathogens for phagocytosis, and activate the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens. Furthermore, IgG is the only antibody isotype that can cross the placenta, providing passive immunity to the fetus.

Classes

There are four subclasses of IgG in humans, named IgG1, IgG2, IgG3, and IgG4. These subclasses differ in their biological properties, functional locations, and ability to interact with other components of the immune system. For example, IgG1 and IgG3 are most effective in complement activation, while IgG4 is known for its anti-inflammatory properties.

Clinical Significance

Abnormal levels of IgG can indicate an underlying disease. High levels may suggest a chronic infection, autoimmune disease, or certain types of cancer. Low levels, on the other hand, may indicate an immunodeficiency disorder, increasing the risk of infections. Measurement of specific IgG antibodies in the blood can be used to diagnose infections and monitor the immune response to vaccines or to determine previous exposure to pathogens.

IgG antibodies are also used in various therapeutic applications, including the treatment of immune deficiencies and autoimmune diseases, as well as in the prevention of infections in individuals with high risk.

See Also

• Immunoglobulin A (IgA)
• Immunoglobulin M (IgM)
• Immunoglobulin E (IgE)
• Immune system
• Antibody
• Vaccine