IgG Vs IgM: Understanding Antibodies in the Immune System

IgG Vs IgM: Introduction
When it comes to understanding the immune system and the role of antibodies in fighting off infections, IgG and IgM are two essential terms that are often mentioned. Antibodies are proteins that help your immune system fight off infections and diseases. They are also known as immunoglobulins (Igs) and they come in different types, such as IgG and IgM.
In this article, we will explore the differences between IgG and IgM antibodies, their functions in the immune system, their diagnostic and clinical significance, and the treatment options based on IgG and IgM levels.

A brief overview of the immune system

The immune system is the body’s defensive mechanism against infections and diseases. It is a complex system consisting of various cells, proteins, and tissues that work together to protect the body from harmful pathogens such as viruses and bacteria.

What are Antibodies or Immunoglobulins?

The immune system is the body’s defensive mechanism against infections and diseases. Antibodies, also known as immunoglobulins (Igs), are proteins produced by the immune system in response to foreign invaders such as viruses and bacteria. The two most abundant types are IgG and IgM antibodies.

What are IgG and IgM antibodies?

IgG vs IgM - Different Immunoglobulins Structures

IgG and IgM antibodies are two of the five classes of antibodies that are produced by B cells, a type of white blood cell that is responsible for the adaptive immune response. The other classes are IgA, IgE, and IgD. Each class of antibody has a different structure, function, and biological property.

IgG Antibodies

IgG antibodies are the most common and abundant type of antibody in the blood and other body fluids. They account for about 75-80% of the total serum antibodies in humans. They have a relatively small size and a long half-life, which means they can circulate in the body for a long time.

They are produced in the later stages of an infection or after vaccination or immunization. They provide long-term protection against pathogens by neutralizing them, opsonizing them (coating them for easier recognition by other immune cells), or activating the complement system (a group of proteins that enhance the immune response).

IgM Antibodies

IgM antibodies are the largest and first type of antibody to be produced in response to a new infection or antigen exposure. They account for about 5-10% of the total serum antibodies in humans. They have a relatively large size and a short half-life, which means they are quickly removed from the body. They are produced in the early stages of an infection or before vaccination or immunization.

They provide short-term protection against pathogens by agglutinating them (clumping them together), activating the complement system, or enhancing phagocytosis (the process of engulfing and destroying pathogens by other immune cells).

Differences Between IgG Vs IgM Antibodies

Antibody Type	IgG	IgM
Size	IgG is the smallest type of antibody in terms of molecular weight	IgM is the largest type of antibody in terms of molecular weight
Location	IgG is found in the blood and other body fluids such as saliva, tears, and breast milk	IgM is found mainly in the blood and lymph fluids
Percentage	IgG is the most abundant type of antibody in the blood, accounting for 75-80% of the total serum antibodies	IgM is the second most abundant type of antibody in the blood, accounting for 5-10% of the total serum antibodies
Production	IgG is produced later in the course of an infection or immune response, or after vaccination or immunization	IgM is produced earlier in the course of an infection or immune response, or before vaccination or immunization
Half-life	IgG is the longest-lasting type of antibody in the body, with a half-life of about 21 days	IgM is the shortest-lived type of antibody in the body, with a half-life of about 5 days
Occurrence	IgG is formed later than IgM antibodies and provides long-term protection against pathogens	IgM is formed earlier than IgG antibodies and provides short-term protection against pathogens
Subclasses	IgG is divided into four subclasses based on their structure and function: IgG1, IgG2, IgG3, and IgG4	IgM is not divided into subclasses
Number of antigen-binding sites	Each IgG molecule has two antigen-binding sites that can recognize and bind to specific antigens on pathogens	Each IgM molecule has ten antigen-binding sites that can recognize and bind to specific antigens on pathogens
Role	IgG is involved in various immune functions such as neutralizing pathogens, coating them for easier recognition by phagocytes (opsonization), activating a group of proteins that enhance the immune response (complement system), killing infected cells by attracting natural killer cells (antibody-dependent cellular cytotoxicity or ADCC), transferring from mother to fetus through the placenta to provide passive immunity, and inhibiting further production of antibodies by B cells (feedback inhibition)	IgM is involved in various immune functions such as clumping pathogens together (agglutination), activating the complement system, enhancing the engulfment and destruction of pathogens by phagocytes (phagocytosis)

IgG Vs IgM Differences

What do IgG Vs IgM antibodies do in the immune system?

IgG and IgM antibodies are important components of the immune system because they recognize and bind to specific antigens on the surfaces of pathogens such as viruses and bacteria. Antigens are substances that cause an immunological response when the immune system recognizes them as foreign. Antibodies designate antigens for destruction by other immune cells or processes by attaching to them.

The activation of the complement system is one of the primary processes by which antibodies kill pathogens. The complement system is a collection of proteins that circulate in the blood and boost the immune response through the production of pores on pathogen membranes, causing them to lyse (bust), or encouraging other immune cells to phagocytose (engulf) them. IgG and IgM antibodies can both activate the complement system by attaching to pathogen antigens and then to complement proteins.

Oponization is another process by which antibodies destroy microorganisms. The process of coating infections with antibodies or other chemicals to make them more recognizable and appealing to phagocytes is known as opsonization. (Immune cells that engulf and destroy pathogens).

Diagnostic Applications of IgG Vs IgM Testing

Screening for infectious diseases:

IgM and IgG tests are used to screen for various infectious diseases such as hepatitis, HIV, and Lyme disease. A positive IgM test indicates an acute or recent infection, while a positive IgG test suggests a past infection or vaccination.

Determining the course of infection:

Measuring IgM and IgG levels at different stages of an infection can help determine the course of the infection. Rising IgM levels indicate an active or recent infection while decreasing IgM levels and rising IgG levels suggest a resolving infection.

Monitoring treatment efficacy:

IgM and IgG tests can be used to monitor the efficacy of treatment for infectious diseases. A decrease in IgM levels and a rise in IgG levels over time suggest that the treatment is effective.

Identifying immune status:

IgG testing is used to determine the immune status of individuals for infectious diseases such as measles, mumps, and rubella. A positive IgG test indicates immunity to the pathogen, either from vaccination or previous infection.

Identifying autoimmune diseases:

Some autoimmune diseases such as lupus and rheumatoid arthritis can cause the production of autoantibodies, including IgG and IgM. Testing for these antibodies can aid in the diagnosis of autoimmune diseases.

IgG Vs IgM in Infectious Diseases

When our bodies come in contact with a foreign substance like a virus, bacteria, or parasite, it triggers our immune system to produce antibodies. Two of the most important antibodies produced by our immune system are Immunoglobulin G (IgG) and Immunoglobulin M (IgM).

Detection of IgG Vs IgM in viral infections

When our body detects a viral infection, it produces IgM antibodies initially. These antibodies are short-lived and are replaced by IgG antibodies, which last longer and provide long-term immunity. Therefore, the detection of IgM antibodies is indicative of a recent viral infection, whereas the presence of IgG antibodies suggests a past infection.

IgG Vs IgM in bacterial infections

IgM antibodies are also produced in response to bacterial infections, but their concentration in the blood is lower than that seen in viral infections. IgG antibodies are the primary type of antibodies produced in response to bacterial infections, and they remain in the bloodstream for an extended period of time, meaning that the detection of IgG antibodies can indicate both current and past bacterial infections.

IgG Vs IgM in parasitic infections

IgM antibodies are also produced in response to parasitic infections, but the concentration in the blood can vary depending on the type and severity of the infection. IgG antibodies may also be produced in response to parasitic infections, but their presence may not indicate active infection.

Clinical Significance of IgG and IgM Levels

Elevated IgG and IgM levels

Elevated levels of IgG and IgM antibodies can be seen in a variety of conditions, including infections, autoimmune diseases, and some types of cancer. Elevated IgM levels can also be seen in certain types of liver diseases.

Decreased IgG and IgM levels

Reduced levels of IgG and IgM antibodies can be seen in immunodeficiency disorders, where the body is unable to produce enough antibodies. This can lead to recurrent infections and an increased risk of infections.

Treatment Options Based on IgG and IgM Levels

Immunoglobulin Replacement Therapy

In patients with immunodeficiency disorders and reduced levels of IgG and IgM antibodies, immunoglobulin replacement therapy may be an option. This therapy involves the administration of IgG antibodies from pooled human blood or recombinant sources.

Targeted Therapies

In some autoimmune diseases and cancers where IgG and IgM levels are elevated, targeted therapies may be used to suppress the immune system and reduce antibody production. These therapies can improve symptoms and slow down the progression of the disease.

Conclusion

In conclusion, IgG and IgM are two crucial antibodies that serve as the primary line of defense against infections. Understanding the differences between these two antibodies can help in the diagnosis, management, and treatment of various infectious diseases. With continued research into the complexities of the immune system, we can continue to develop new treatment options and improve patient outcomes.

FAQ

What is the difference between IgG Vs IgM antibodies?

IgG is the most abundant antibody and is responsible for long-term immunity. It is smaller and more flexible than IgM and can cross the placenta, providing passive immunity to the fetus. IgM, on the other hand, is the first antibody produced during infection and is responsible for the immediate immune response. It is larger and more rigid than IgG but does not cross the placenta.

How are IgG and IgM antibodies used in diagnosing infections?

IgG Vs IgM antibodies can be detected in blood samples using serological testing. This process involves exposing the blood sample to an antigen related to the suspected infection and measuring the levels of IgG and IgM antibodies produced. Elevated levels of IgM antibodies indicate an acute infection, while elevated levels of IgG antibodies indicate previous exposure or long-term immunity.

What does it mean if someone has low levels of IgG or IgM antibodies?

Low levels of IgG or IgM antibodies can indicate an immunodeficiency disorder, which means that the immune system is unable to respond appropriately to infections. This can be caused by a genetic mutation or exposure to immunosuppressants such as chemotherapy. In some cases, low levels of IgG or IgM antibodies may also be seen in elderly individuals, but this is typically not a cause for concern.

Can IgG and IgM antibodies be used to develop vaccines?

Yes, IgG and IgM antibodies are often used as a basis for developing vaccines. Vaccines work by introducing an antigen that stimulates the production of IgG and IgM antibodies, providing immunity without the risk of infection. This approach has been successful in developing vaccines for diseases such as polio, measles, and hepatitis B.

References

Difference Between Antibody Test IgG and IgM. (n.d.). Retrieved from http://www.differencebetween.net/science/difference-between-antibody-test-igg-and-igm/
Immunoglobulin Test: High vs Low vs Normal Levels of (Ig) Antibodies. (2021, August 19). Retrieved from https://www.webmd.com/a-to-z-guides/immunoglobulin-test
What IgG & IgM Antibodies Mean for Lyme Disease | IGeneX. (2022, August 9). Retrieved from https://igenex.com/tick-talk/igg-vs-igm-antibodies-and-what-they-mean-for-lyme-disease-tests/

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