Immunoglobulin g

Immunoglobulin G (IgG) is a type of antibody representing approximately 75% of serum antibodies in humans. IgG is the most common type of antibody found in blood circulation. It is created and released by plasma B cells. Each IgG has two antigen binding sites.

Structure

Immunoglobulin G antibodies are composed of two heavy chain–light chain pairs (half-molecules), which are connected via disulfide bonds located in the hinge region. The structural characteristics of the hinge region determine the isotype (subclass) of an IgG antibody.

Subclasses

There are four subclasses of IgG in humans, named in order of their abundance in serum (IgG1 being the most abundant):

• IgG1: Makes up approximately 60-65% of the total IgG antibodies.
• IgG2: Makes up approximately 20-30% of the total IgG antibodies.
• IgG3: Makes up approximately 5-10% of the total IgG antibodies.
• IgG4: Makes up approximately 4-6% of the total IgG antibodies.

Function

IgG antibodies are involved in the secondary immune response. They are responsible for the majority of antibody-dependent cellular cytotoxicity and are involved in fighting against viral and bacterial infections. IgG antibodies can pass through the human placenta, thereby providing protection to the fetus in utero.

Clinical significance

Abnormalities in IgG levels can occur in a number of health conditions, including immunodeficiency and autoimmune diseases. Measurement of specific IgG antibodies in patient serum is a common diagnostic tool for infectious disease determination.

See also

• Antibody
• Immunoglobulin A
• Immunoglobulin M
• Immunoglobulin E
• Immunoglobulin D

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