When the body detects a threat from pathogens such as bacteria, germs, and viruses, the plasma cells produce a special kind of protein called immunoglobulins (also called antibodies). Â The smallest and also the most common type of immunoglobulins is the IgG antibodies. These antibodies make up around 75%-80% of all the immunoglobulins in the body. They can be found in body fluids such as the blood, peritoneal fluid, lymph fluid, and cerebrospinal fluid.
IgG antibodies play an important role in warding off viral and bacterial infections. They also reproduce and defend the body from harmful foreign substances and toxins that enter the body. Moreover, this type of antibodies is the only one which can pass through the placenta to help pregnant women protect the fetus.
There are four subclasses under IgG called IgG1, IgG2, IgG3, and IgG4. The total IgG is comprised of 60% to 65% IgG1, 20% to 25% IgG2, 5% to 10% IgG3, and less than 4% IgG4. IgG1 is the type which is responsible for the immune response mediated by the thymus. This subclass of IgG counters polypeptides and protein antigens. Moreover, the normal concentration of IgG1 is achieved during infancy, and a low level is considered a symptom of Hypogammaglobulinemia.
On the other hand, IgG2 is the subclass which is responsible for the immune response against polysaccharide or carbohydrate antigens. The typical concentration is reached when the person is around 6 to 7 years old. Furthermore, IgG2 deficiency is normally associated with respiratory infections that are recurrent.
Just like IgG1, IgG3 also plays an integral part in fighting polypeptides and protein antigens. The specific role of IgG4, on the other hand, is still unknown. However, high levels of IgG4 are associated with interstitial pneumonia, sclerosing pancreatitis, cholangitis, and food allergies.
The body produces IgG, in general, as a delayed reaction to infections. Because this type of antibodies can last in the body for extended periods of time, it is useful for passive immunity.