IgM vs IgG: Difference and Comparison

In the human body, the immune system produces many antibodies in return for any foreign material entering it. These antibodies are specified to their binding site and binding molecule.

Also, these antibodies are classified into many different types: IgE, IgA, IgM, IgD, and IgG. All the above antibodies consist of the heavy and light chain and differ in shape, size, function, etc.

Key Takeaways

  1. IgM antibodies are the first to respond to infections, providing short-term immunity.
  2. IgG antibodies develop later in the immune response, offering long-lasting protection.
  3. IgM antibodies exist as pentamers, while IgG antibodies are monomeric in structure.

IgM vs IgG

IgM is the first antibody produced by the immune system when it encounters a new infection and is effective in neutralizing pathogens and triggering an immune response. IgG is the most common antibody produced by the immune system and is effective in neutralizing pathogens and providing long-term immunity.

IgM vs IgG

IgM belongs to the class of antibodies with a pentamer structure formed by five molecules of IgM. The occupancy of the antibody in the blood and lymph is around 10%.


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Among every other antibody present in the body, IgM is the biggest. When any foreign particle, virus, bacteria, etc., enters the body, it is the first of them that is released.

IgG is also one of the types of antibody released within the human body after any immune response made by the immune system of the human body.

It is considered the most abundant one in the blood and the only one that can travel through the placenta of the mother to the unborn child.

Comparison Table

Parameters of ComparisonIgMIgG
DefinitionThe structure of the molecule is in pentameric form and contains a primary antibodyA class comprising with ample type of antibody
SizeBig (970kDa)Small and is 150kDa
Stands forImmunoglobulin MImmunoglobulin G
SubclassesNoFour – IgG1, IgG2, IgG3, IgG4
Abundance LessMore
ReleasedEarly stageLater stage
Placenta CrossingNoYes
UnitFrom five unitsSingle
LocationLymph and bloodBody fluids
Antigen binding sites102
RoleAgglutination and cytosolic reactionsActivates the complement system of the body
Life spanTemporary or short-termLong lasting
ProtectionNew pathogensViral and bacteria

What is IgM?

IgM is the acronym that is used for the term immunoglobulin M. It is one of the classes present as the antibody in the human body. In general, there are five different classes of antibodies, and IgM is one of them.

And the approximate abundance of the antibody in the body is about 10%. These antibodies are released in the body just immediately after any foreign body in an individual body.

The antibody’s size and weight are big and approximately 970kDa. The structure of the molecules is made with five units with a primary antibody.

Unlike IgG, they can not cross the placenta from mother to child. These are generally found in the lymph and blood and are responsible for agglutination and cytosolic reactions. On the antibody, approximately ten different paratopes are present.

What is IgG?

IgG antibody is the acronym for the term Immunoglobulin G. It is one of the other five different classes of the antibody found in the human body.

The basic definition states that it is a molecule with copious antibodies in the body. Approximately in number, the blood or the other body fluid combination has had about 75 % of them.

The structure of the antibody is made with a single unit which is why the size of the antibody is less and is approximately about 150kDa. This antibody gives a later response to any foreign material entering the individual body.

The key role of the antibody is that it is the only immunoglobulin that can cross the placenta, attaching the mother and the unborn child. On further classification, it can be subdivided into four classes, and they are – IgG1, IgG2, IgG3, and IgG4.

They are found in the blood and the body fluids present. Unlike IgM, they have only two paratopes on their molecule.

Main Differences Between IgM and IgG

  1. IgM antibody is said to be a molecule having a structure of pentameric form and has a primary antibody, whereas comparatively, on the other hand, IgG antibody is said to be a class with abundant antibodies.
  2. The size of the antibody IgM is big and is about 970 kDa, whereas comparatively, on the other hand, the size of the IgG is small and is 150 kDa.
  3. The IgM is used as the acronym for Immunoglobulin M, while comparatively, on the other hand, the IgG is used for the acronym Immunoglobulin G.
  4. IgM has no other subclasses further, while comparatively, on the other hand, the IgG has further subclassification and is divided into four classes – IgG1, IgG2, IgG3, and IgG4.
  5. The amount of antibody IgM is ample in the human body, whereas comparatively, on the other hand, the amount of IgG antibody is less.
  6. IgM is the first antibody that is released, while on another side, IgG is released in the body with later responses. 
  7. IgM can’t cross the placenta, while IgG is the only antibody present in the human body that can cross the placenta.
  8. The structure of the IgM is made up of a single unit, while the structure of IgG is made up of a single unit.
  9. The antibody IgM is found to be in lymph and blood, while IgG is found to be in body fluids. 
  10. IgM has a total of 10 antigen-binding sites, while IgG has a total number of 2 antigen-binding sites. 
  11. The antibody IgM function is to perform cytosolic reactions and to do agglutinations, while the antibody IgG functions to activate the complement system.
  12. The life span of the IgM is small, while the life span of the IgG is large.
  13. IgM protects majorly from new pathogens, while IgG protects from virus and bacteria.
Difference Between X and Y 2023 06 07T092311.385
  1. https://www.sciencedirect.com/science/article/pii/S1567576920338285
  2. https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-131-2-377?crawler=true
  3. https://europepmc.org/article/med/8586880
  4. https://www.sciencedirect.com/science/article/abs/pii/016158909390044C
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