Activation-induced cytidine deaminase

Definition

Activation-induced cytidine deaminase (AID) is an enzyme crucial for the process of somatic hypermutation and class switch recombination in B cells. By converting cytidine residues in DNA to uracil, AID plays a vital role in enabling B cells to produce high-affinity antibodies and switch antibody classes, which are essential for a robust immune response.

5 Must Know Facts For Your Next Test

1. AID is primarily expressed in activated B cells during immune responses and is essential for generating high-affinity antibodies.
2. The action of AID leads to DNA breaks that initiate the class switch recombination process, allowing B cells to change the isotype of antibodies they produce.
3. Deficiencies in AID can result in immunodeficiencies, as B cells fail to undergo somatic hypermutation and class switching effectively.
4. AID targets regions of immunoglobulin genes known as switch regions for class switch recombination, which are rich in repetitive sequences.
5. The enzyme's activity is tightly regulated to prevent unwanted mutations that could lead to issues like autoimmunity or lymphomagenesis.

Review Questions

• How does activation-induced cytidine deaminase contribute to the generation of high-affinity antibodies in B cells?
  • Activation-induced cytidine deaminase facilitates somatic hypermutation by converting cytidine to uracil in the DNA of immunoglobulin genes. This introduces mutations in the variable regions of the genes, which leads to the production of antibodies with increased affinity for their target antigens. As a result, B cells can better adapt and respond to specific pathogens during an immune response.
• Discuss the implications of AID activity on class switch recombination and how it affects the immune response.
  • AID plays a critical role in class switch recombination by targeting switch regions of immunoglobulin genes, allowing B cells to change the type of antibody they produce. This ability to switch classes enhances the immune response by enabling the production of different antibody isotypes, which can engage various effector mechanisms more effectively. For instance, switching from IgM to IgG allows antibodies to better penetrate tissues and enhance opsonization.
• Evaluate the potential consequences of dysregulation of activation-induced cytidine deaminase activity in immune system function.
  • Dysregulation of AID activity can lead to severe consequences for immune system function, including autoimmune disorders due to excessive mutations or lymphomas caused by improper DNA repair mechanisms following AID's action. If AID introduces too many mutations without proper checks, it may result in self-reactive B cells that attack the body's own tissues. On the flip side, insufficient AID activity can compromise antibody diversity and effectiveness, leaving individuals vulnerable to infections.

Related terms

Somatic Hypermutation: A process that introduces mutations into the variable region of immunoglobulin genes in B cells, increasing the affinity of antibodies for their specific antigens.

Class Switch Recombination: A biological mechanism that changes a B cell's production of immunoglobulin from one class to another, allowing for diverse antibody functions.

Uracil-DNA Glycosylase: An enzyme that recognizes uracil in DNA and removes it, playing a role in DNA repair processes after AID acts on cytidine residues.