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Difference Between Somatic Hypermutation and Class Switching

Somatic hypermutation is when a genetic mutation happens in the variable region of antibodies. 

What is Somatic Hypermutation?


Somatic hypermutation can be defined as the process when mutations happen in some of the bases in the V region of B cell antibodies. The V region is known as the variable region of the antibody, and it is a particular section of the molecule. 


Somatic hypermutation happens because of the activity of a specific enzyme called activation-induced cytidine deaminase. This enzyme triggers the point mutations.


The benefit of somatic hypermutation is that it leads to affinity maturation. This all helps the immune response to function better since the response to antigens is stronger.


Although it is very rare, the point mutations of somatic hypermutation can end up producing oncogenes. If oncogenes become active, they can result in uncontrolled cell proliferation, which then can lead to malignant cancer.

What is Class Switching?


Class switching is when a B lymphocyte changes its function from making one antibody to making another antibody. In class switching, what happens is that the antibodies IgD and IgM are switched for a different class of antibodies, namely, the IgA, IgE, and IgG antibodies.


The immunoglobulins of the B cells can be switched in response to specific molecules binding to cytokine receptors and CD4 receptors. The receptors are proteins that occur on the membranes of cells and function as docking sites for molecules. While the process of class switching can happen naturally; this can also happen as a result of a person getting immunized against some pathogen. 


Class switching occurs by recombination and it is generally considered to be beneficial for the immune system because it improves the immune response to pathogens. 


If class switching does not progress correctly, there is a risk of cancer. For instance, Burkitt’s lymphoma has been associated with errors in class switching. 

Difference between Somatic Hypermutation and Class Switching?


Somatic hypermutation is when genetic changes occur in the V region of antibodies. Class switching is when there is a switch from one set of antibodies to another.


Enzyme activation-Induced cytidine deaminase is the trigger that causes somatic hypermutation to occur. It is the binding of specific binding molecules to cytokine receptors and CD4 receptors that trigger class switching.

Method involved 

In the case of somatic hypermutation, point mutations are involved that involve the G and C bases. In the case of class switching, recombination is involved.

Cells where it occurs

Somatic hypermutation occurs in germinal center B cells. Class switching occurs in mature B cells.

Region of antibody affected

It is the variable region (V region) that is affected in somatic hypermutation. It is the constant region (C region) of the antibody that is affected in class switching.


Somatic hypermutation allows for affinity maturation which helps the immune system to respond more strongly to foreign antigens. Class switching enables B cells to respond to different antigens, which also helps the immune response in responding to new pathogens.


Mistakes can occur during somatic hypermutation, although this is uncommon, these mistakes can end up producing oncogenes, that can form cancer malignancies. Mistakes can happen in class switching, which can also produce cancers, such as Burkitt’s lymphoma. 

Table comparing Somatic Hypermutation and Class Switching

Summary of Somatic Hypermutation and Class Switching

  • Both somatic hypermutation and class switching are important processes that enhance the immune response.
  • Somatic hypermutation occurs in the variable region and involves point mutations.
  • Class switching occurs in the constant region and involves recombination.
  • Both class switching and somatic hypermutation can, on the rare occasion, cause cancer.


Is somatic hypermutation class switching?

No, somatic hypermutation is not the same as class switching. Somatic hypermutation refers to genetic changes related to point mutations, while class switching refers to changes due to recombination.

What is the difference between somatic hypermutation and VDJ?

Somatic hypermutation is the process where point mutations occur in the V region of antibodies of the B cells. VDJ is a form of recombination, which leads to class switching.

Where do B cells undergo somatic hypermutation and class switching?

Somatic hypermutation occurs in the germinal B cells while class switching occurs in the mature B cells.

What is the purpose of somatic hypermutation?

Somatic hypermutation is a way for the body to improve on the immune response. It does this via this process of mutation, which then allows for affinity maturation of the B cells.

What do you mean by class switching?

Class switching is when antibodies on the B cell are switched to different antibodies.

Where does class switching occur?

Class switching occurs in the B lymphocytes.

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References :

[0]Chi, Xiying, Yue Li, and Xiaoyan Qiu. "V (D) J recombination, somatic hypermutation and class switch recombination of immunoglobulins: mechanism and regulation." Immunology 160.3 (2020): 233-247.

[1]Janeway Jr, Charles A., et al. "The generation of diversity in immunoglobulins." Immunobiology: The Immune System in Health and Disease. 5th edition. Garland Science, 2001.

[2]Pilzecker, Bas, and Heinz Jacobs. "Mutating for good: DNA damage responses during somatic hypermutation." Frontiers in immunology 10 (2019): 438.

[3]Image credit: https://www.canva.com/photos/MADBB3OqYUI-antibodies-in-the-blood/

[4]Image credit: https://www.canva.com/photos/MADDOeoAdn8-antibodies-and-a-cancer-cell/

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