What is the Difference Between Somatic Hypermutation and Affinity Maturation

The main difference between somatic hypermutation and affinity maturation is that somatic hypermutation is a component of affinity maturation, whereas affinity maturation is a cellular mechanism in which the immune system adapts to new foreign elements confronting it.

Somatic hypermutation and affinity maturation are mechanisms by which the immune system adapts to recognize better and neutralize pathogens.

Key Areas Covered

1. What is Somatic Hypermutation
– Definition, Features, Importance
2. What is Affinity Maturation
– Definition, Features, Importance
3. Similarities Between Somatic Hypermutation and Affinity Maturation
– Outline of Common Features
4. Difference Between Somatic Hypermutation and Affinity Maturation
– Comparison of Key Differences

Key Terms

Affinity Maturation, Somatic Hypermutation

What is Somatic Hypermutation

Somatic hypermutation is a cellular process in which the accumulation of point mutations occurs in the V-regions of both the heavy and the light chain of the antibody. Also, this mutation rate is 10⁶-fold higher than the background mutation rate. Additionally, it occurs in the centroblast stage of the B cell differentiation that occurs in the germinal centers of the secondary lymphoid organs. Notably, the overall goal of somatic hypermutation is to produce high-affinity antibodies. But, the process of somatic hypermutation is unable to distinguish favorable mutations from unfavorable mutations. Therefore, it produces non-functional antibodies that do not fold or can harbor premature stop codons.

Figure 1: Somatic Hypermutation

Furthermore, a selection process for new antibodies occurs in the light zone of the germinal center to select B cells that can produce high-affinity antibodies. Therefore, more mutations can be carried by the high-affinity antibodies. However, mutations accumulate in the complementarity-determining regions (CDRs) of the antibody V genes. Hence, CDRs regions are in direct contact with antigens.

What is Affinity Maturation

Affinity maturation is an essential process in antibody optimization. It generates antibodies for second-generation therapeutics. Repeated exposure to some antigens induces the host to produce antibodies with an increased affinity to antigens. Thus, during the secondary immune response, it generates antibodies with a several-fold greater affinity to antigens than the primary immune response. On the other hand, affinity maturation occurs in the germinal centers of the secondary lymphoid organs. The two main processes of affinity maturation are somatic hypermutation and clonal selection.

Figure 2: Affinity Maturation

Moreover, somatic hypermutation is the accumulation of a higher proportion of mutations in the V-regions of both light and heavy chains to bring variability to the antigen-binding regions of the antibody. In the clonal selection step, these mutations are selected to get the antibodies with a higher affinity to the exposed antigen. Both processes occur in the germinal centers of the secondary lymphoid organs.

Similarities Between Somatic Hypermutation and Affinity Maturation

• Somatic hypermutation and affinity maturation are two processes by which the immune system adapts to new foreign elements.
• It occurs during class switching.

Difference Between Somatic Hypermutation and Affinity Maturation

Definition

Somatic hypermutation refers to a process in which point mutations accumulate in the antibody V-regions of both the heavy and light chains, while affinity maturation refers to the process by which B cells increase their affinity for a particular antigen.

Type of Process

Somatic hypermutation is a genetic process, while affinity maturation is a cellular process.

Importance

Somatic hypermutation is a component of affinity maturation, while affinity maturation is the primary process of adapting to foreign elements.

Conclusion

In brief, somatic hypermutation and affinity maturation are two processes of adapting antibodies to foreign antigens. Somatic hypermutation is a process of accumulating point mutations in the V-regions of both heavy and light chains. It is a genetic process and also a component of affinity maturation. In comparison, affinity maturation is the primary process of adapting antibodies to foreign antigens. However, it is a cellular process. Therefore, the main difference between somatic hypermutation and affinity maturation is the type of process.

References:

1. Somatic hypermutation. Somatic Hypermutation – an overview | ScienceDirect Topics. (n.d.). 
2. Affinity maturation. Affinity Maturation – an overview | ScienceDirect Topics. (n.d.). 

Image Courtesy:

1. “Somatic hypermutation v5” By Rashedul Islam Rony – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Germinal center” By Billy10drs – Own Work (CC-BY SA 3.0) via Commons Wikimedia