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Immunoglobulin G (IgG) - Functions and Deficiency

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IgG is the principal antibody the body produces as a part of the secondary immune response to an antigen. Read the article below to know more.

Medically reviewed by

Dr. Mohammad Rajja

Published At November 1, 2022
Reviewed AtNovember 1, 2022

Introduction

When a foreign substance or organism enters the body, the immune system identifies the attack and produces special proteins called immunoglobulins. These are made and released by plasma cells. Having fewer immunoglobulins in the body makes one susceptible to infections. Too many immunoglobulins in the body could indicate allergies or an overactive immune system.

What Are the Types of Immunoglobulins?

The body produces different types of immunoglobulins:

  • Immunoglobulin A (IgA).

  • Immunoglobulin G (IgG).

  • Immunoglobulin M (IgM).

  • Immunoglobulin D (IgD).

  • Immunoglobulin E (IgE).

What Are IgG Antibodies?

Immunoglobulin G is the most common type of antibody, representing almost 75 % of the total serum antibodies. It is the main antibody in the blood and extracellular fluid and protects the body from infections by binding to bacteria, viruses, and fungi. Immunoglobulin G is the only immunoglobulin that can cross the placenta in mothers and is responsible for protecting the newborn during the first months of life. These are often used in immunological research and clinical diagnostics because of their relative abundance. IgG has four subclasses: IgG1, IgG2, IgG3, and IgG4, named in order of their abundance in the serum.

What Are the Functions of IgG?

Immunoglobulin G antibodies are the smallest but the most abundant in the body. They help in providing secondary immune responses in the body. Functions of IgG include:

  • IgG binds to the pathogen and causes their immobilization.

  • IgG coating on the pathogen surface helps the phagocytic cells recognize and ingest them.

  • IgG activates a pathway for a cascade of immune protein production that helps in pathogen elimination.

  • IgG helps neutralize toxins.

  • IgG is the only antibody that passes through the human placenta and helps protect the fetus in utero.

  • IgG is secreted in the breast milk, and the IgG that passes through the placenta helps provide the infant with humoral immunity before the immune system develops.

What Are IgG Deficiencies?

IgG deficiency refers to a condition in which the body does not produce enough IgG (immunoglobulin G) antibodies. IgG protects the body against infections by binding to microorganisms, immobilizing and eliminating them. Hence, IgG deficiency makes the body more susceptible to infections, as the immune response against microorganisms like bacteria, viruses, and fungi gets impaired. The most common deficiency of IgG subclasses in early childhood is IgG2 deficiency, whereas, in adults, IgG1 and IgG3 deficiencies are more common. In addition, the development of IgG2 and IgG4 is slower in children compared to IgG1 and IgG3 levels. However, in some children, the complete development of the whole range of IgG subclasses can be delayed until the teenage years.

What Causes IgG Deficiencies?

The cause of primary immunoglobulin G deficiency is not apparent, but genetics may play a role.

IgG deficiency can be caused by:

What Are the Symptoms of IgG Deficiency?

IgG deficiency affects both children and adults. Infections that can affect people with the condition include:

  • Gastrointestinal infections.

  • Ear infections.

  • Pneumonia.

  • Sinus infections.

  • Respiratory problems.

  • Sore throat.

  • Bronchitis.

  • Severe and life-threatening infections.

How Is IgG Deficiency Diagnosed?

The level of immunoglobulins in the body is diagnosed through a blood test. An immunoglobulin test helps measure the levels of different types of immunoglobulins in the body. An individual may have an optimum total IgG level; hence it is crucial to test the concentration of the subclasses of IgG as well. Children lower than 24 months of age cannot make IgG2 antibodies; therefore, measuring levels of IgG2 before this age is not recommended.

What Is an Immunoglobulin Test?

It is a test that measures the level of different types of antibodies or immunoglobulin in the blood. The body produces antibodies to protect against bacteria, viruses, and allergens. The immunoglobulin produced for each type of infection is different; for example, the antibodies against measles are not the same as the antibodies for mononucleosis. Hence diagnosing the antibody produced helps identify an infection in the body. Sometimes the body may produce antibodies against its cells and organs, which is an autoimmune disorder.

How Is IgG Deficiency Treated?

The treatment for IgG deficiency depends upon the time of onset of symptoms and their severity. Symptoms that appear later in life are harder to manage, and the person will also be susceptible to further infections. The primary objective of treatment includes the appropriate use of antibiotics to treat and prevent infections. The type of antibiotic used and the duration of treatment would depend on the type and severity of the infection. Intravenous administration of 300 - 600 mg/kg of IgG once every three to four weeks, or 100 - 200 mg/kg/wk subcutaneously, is the currently recommended therapy. In patients with chronic sinopulmonary infections, higher doses are more effective. Although IgG replacement therapy has shown to be effective in appropriate patients, intravenous IgG may have infusion-related adverse effects. For example, three to 12 % of the treated patients developed myalgia, headache, fever, chills, and mild nausea. However, subcutaneous IgG replacement therapy was associated with local infusion site reactions and free from systemic reactions. Patients with persistent IgG deficiencies and frequent infections with optimum anti-polysaccharide antibodies must also be treated using adequate prevention, vaccine, and antibiotic therapy.

Conclusion

IgG is the smallest and the most abundant antibody in the serum and constitutes 75 % of the total serum. It helps in protecting the body from infections by binding to the microorganism, immobilizing, and eliminating the pathogen. It also helps neutralize toxins. Immunoglobulin G is the only antibody that can pass through the placenta; hence they play an essential role in the humoral immunity of the fetus in utero and during the first few months after birth. The deficiency of IgG antibodies makes a person more susceptible to infections, and an abundance than required of IgG develops allergies and an overactive immune response. IgG deficiency can be treated with IgG replacement therapy. If one is diagnosed with IgG deficiency, consult the healthcare provider whenever there is a sign of infection, including a minor cold.

Frequently Asked Questions

1.

What Are the Functions of Immunoglobulin G?

Immunoglobulin G (IgG) is the most common type and constitutes about 75 % of human antibodies. It helps prevent infections, so their decrease can lead to increased susceptibility to infections. They multiply among themselves and destroy any foreign substances entering the human body.

2.

What Does a High IgG Level Indicate?

High levels of immunoglobulin G indicate an existence of a chronic infection, inflammation, autoimmune disorders, or plasma cell disorders. For example, the levels are higher in conditions such as multiple myeloma, multiple sclerosis, and long-term hepatitis.

3.

What Does an IgG Test Determine?

The immunoglobulin G test determines the level of IgG antibodies present in the blood. This indicates if a person is immune to a condition or if their immune system is not working. In addition, immunoglobulin tests are used to determine allergies or autoimmune disorders.

4.

What Does a Low IgG Level Indicate?

Immunoglobulins or antibodies are proteins produced by the plasma cells against a pathogenic attack. Therefore, IgG deficiency is considered a significant health concern where the body cannot produce enough IgG, possibly due to aging, malnutrition, chemotherapy, and infections. Hence, individuals with low IgG levels are prone to infections.

5.

Is Stress a Factor Causing High IgG?

Studies reveal that individuals with high-stress perception show increased IgG, IgA, and IgM levels, but not under low-stress conditions. In addition, acute stress increases humoral and cellular-mediated immunity, thereby causing the resolution of infections.

6.

What Is an Ideal IgG Level?

The immunoglobulin G levels vary in different age groups. They are between 688 and 1251 mg per 100 ml in males and from 720 to 1038 mg per ml in females. If IgG levels are less than 400 mg/ml, they are low, and if they are greater than 16 g/L, they indicate high levels of IgG.

7.

Can IgG Cause Inflammation?

Immunoglobulin G has two opposite functions. One is to induce proinflammatory responses and establish immune cells when any infectious pathogen enters the body. The other one is to produce an anti-inflammatory treatment response when administered intravenously. However, the proinflammatory response is the advanced function of the two.

8.

How Common Is IgG Deficiency?

IgG deficiency contributes to 10% to 15% of the world population and has a non-specific clinical significance. However, studies have shown that many patients with low levels of IgG are often asymptomatic, and only a few patients with selective IgG deficiency can be identified with severe infections.

9.

Is Age a Risk Factor for IgG Deficiency?

A significant drop in immunoglobulin G levels can be noted in older individuals, whereas IgA levels show no major decline with aging. Like many other physiological functions, immune activity also decreases with age.
Dr. Mohammad Rajja
Dr. Mohammad Rajja

General Practitioner

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