IgG

IgG or Immunoglobulin G is a type of antibody that plays a crucial role in the immune system. It is the most common type of antibody found in the circulation, making up between 75% to 85% of all antibodies in the human body.

Structure

IgG antibodies are composed of two heavy chains and two light chains, forming a Y-shaped structure. The two arms of the Y, known as the Fab region, contain the antigen-binding sites, while the stem, or Fc region, interacts with various cells and proteins of the immune system.

Function

IgG antibodies are involved in the secondary immune response, which is the immune system's reaction to re-exposure to an antigen. They can neutralize toxins, viruses, and bacteria by binding to them and preventing them from entering cells. IgG antibodies can also activate the complement system, a group of proteins that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promotes inflammation, and attacks the pathogen's cell membrane.

Subclasses

There are four subclasses of IgG in humans, named IgG1, IgG2, IgG3, and IgG4. Each subclass differs in its biological properties, and the distribution of these subclasses varies in different types of immune responses.

Clinical significance

Abnormal levels of IgG can indicate a problem with the immune system. High levels can be seen in chronic infections and autoimmune diseases, while low levels can indicate an immune deficiency. Measurement of specific IgG antibodies in the blood can also be used to determine immunity to specific infections, such as measles, mumps, and rubella.

See also

• Antibody
• Immune system
• Antigen
• Complement system
• Autoimmune disease
• Immune deficiency

IgG Resources
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