What are immunoglobulins and what do they do?

Immunoglobulins are specialized proteins that defend the body against infections and play a vital role in the immune system. They are important in medicine for diagnosing diseases, treating immune disorders and developing targeted therapies. So how do immunoglobulins work and why are they so vital? In this article, we will cover the different types, functions and wide-ranging uses of immunoglobulins in modern medicine.

What are immunoglobulins?

Immunoglobulins also known as antibodies, are specialized proteins produced by immune cells called B cells, that play an important role defending the body against infections caused by bacteria, viruses, and the toxins produced by these agents. They work like a precise lock-and-key, where each antibody is uniquely shaped to bind to a specific substance, called an antigen, and tag it for destruction. Specialized white blood cells, for example, macrophages, can then recognize and destroy the bacteria and viruses, preventing infections.

The discovery of immunoglobulins dates to the late 19th century, a revolutionary era in the study of the immune system, when bacteria and viruses were identified as the cause of many diseases – the germ theory of diseases. 

Over time, scientists have discovered the structure and functions of immunoglobulins, leading to a better understanding of the immune system and improving the treatment of diseases. Today, immunoglobulins are recognized as a very important part of the immune response, essential for maintaining good health and fighting infections.

Why are immunoglobulins important in health?

Immunoglobulins are essential in modern medicine. They are important in treating and diagnosing many diseases, particularly in these areas:

• Treatment of immune deficiencies: People with primary and secondary immunodeficiencies cannot produce enough antibodies. They depend on receiving medicines containing immunoglobulins to replenish their antibody levels so they can prevent infections more effectively and live longer lives. 
• Treatment of autoimmune diseases: With these conditions, the immune system attacks healthy cells by mistake. High doses of immunoglobulins are used to treat autoimmune conditions affecting the nervous system such as Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP) and myasthenia gravis. Immunoglobulins work in these diseases by turning down the activity of the autoimmune response and reducing the inflammation caused by overactivity.
• Infection prevention: Immunoglobulins can also help prevent infectious diseases in people who are exposed to viruses and bacteria such as hepatitis, tetanus and rabies. By providing antibodies specifically made to fight these bacteria and viruses, they help to prevent the development of the diseases.

What are the different types of immunoglobulins?

There are several types of immunoglobulins. Humans have five classes, or isotypes, of immunoglobulins, each one playing a different protective role in the immune system:

IgG  

• IgG is the most abundant immunoglobulin by far, making up 70% to 80% of antibodies in the blood and the fluid that surrounds cells in the body. It provides long-lasting protection after infections and vaccinations, neutralizing bacteria and viruses and aiding in their removal.
• IgG is the only immunoglobulin that crosses the placenta, allowing the mother’s antibodies to pass to the baby in the womb.

IgA

• IgA acts as the first line of defense against infections at entry points like the surfaces inside the nose, mouth and throat.
• It’s found in the trachea and lungs and also in the stomach and intestines where it provides local protection. IgA is also found in saliva, tears and breast milk.

IgM

• IgM is the first antibody the body produces when an infection starts, launching an immediate but short-lived defense. 
• It circulates in blood and lymphatic fluid, where it forms large complexes with antigens to neutralize bacteria and viruses.
• Its rapid response is crucial for combating infections while the immune system builds up its defense for a long time.

IgE

• IgE plays a key role in allergic reactions, binding to the substances causing allergies and triggering the release of histamine, causing itching, swelling and other allergic responses. It also defends against parasitic infections, especially worms.

IgD

• IgD is the least understood immunoglobulin, but it is believed to help activate and regulate B cells, which produce antibodies.
• It is found in small amounts in the blood and is mainly located on the surface of immature B cells.

How do immunoglobulins work?

Immunoglobulins protect the body from harmful bacteria, viruses, and parasites through a series of steps:

Step 1: Recognition of threats  

Immunoglobulins recognize and bind to specific substances called antigens, located on the surface of bacteria, viruses or parasites. This lock-and-key targeting ensures a narrowly aimed response.

Step 2: Neutralization of pathogens

Once attached, immunoglobulins block the ability of the bacteria or virus to infect healthy cells, preventing the spread of infection.

Step 3: Activating the immune response

Immunoglobulins help trigger the body’s defenses by targeting the bacteria and viruses and signaling immune cells such as macrophages to destroy the pathogens. 

Step 4: Building long-term immunity

After encountering pathogens, the immune system develops long-lasting immune memory, enabling B cells to produce immunoglobulin (IgG) faster and more robustly if the same bacteria or virus reappears. 

Applications

Immunoglobulins have a wide range of uses in immunology, healthcare and research settings, including:

Therapeutics

• Immunoglobulins are used in immunology to treat people with immune systems that do not function as they should (immune deficiencies), people whose immune systems have attacked their own bodies (autoimmune disorders) and people with overactive immune systems causing inflammation in parts of the body (inflammatory conditions).
• They are administered through the vein, intravenously (IVIG), or under the skin, subcutaneously (SCIG), to boost the immune system. 
• Immunoglobulin therapy contains primarily IgG.

Diagnostics

• Immunoglobulins are needed for antibody-based diagnostic tests, such as ELISA (enzyme-linked immunosorbent assay), which detect illnesses caused by germs, such as human immunodeficiency virus (HIV) and COVID-19.

Research and development

• They are crucial for studying immune responses, developing vaccines and for targeted therapies in cancer and other diseases.

Immunoglobulins are an essential tool in modern medicine, playing a key role in immune protection, and diagnosis and treatments for a variety of conditions. Understanding their benefits helps patients, researchers and healthcare professionals appreciate their impact on global health. Want to learn more about related topics? Explore our medical glossary here.