Immunoglobulin class switching

Immunoglobulin Class Switching

File:Immunoglobulin class switching.png

Schematic representation of Immunoglobulin class switching

Immunoglobulin class switching, also known as isotype switching, class-switch recombination (CSR), or Ig class switching, is a biological mechanism that changes a B cell's production of immunoglobulin from one type to another, such as from the isotype IgM to the isotype IgG.

Overview

During an immune response, B cells are stimulated to produce antibodies of different classes, each with a unique effector function. This process is regulated by the cytokine environment and is initiated by the activation-induced cytidine deaminase (AID) enzyme.

Mechanism

File:Mechanism of Immunoglobulin class switching.png

Mechanism of Immunoglobulin class switching

The process of class switching involves a DNA recombination event that deletes the constant region genes for one isotype and brings a new constant region gene, corresponding to a different isotype, into proximity with the variable region gene. This process is mediated by AID, which deaminates cytosine residues in DNA to uracil. The resulting U:G mismatches are processed into DNA breaks, which are then repaired by non-homologous end joining (NHEJ), leading to the recombination event.

Role in Immunity

Class switching is crucial for the immune system's ability to fight off different types of infections. For example, IgG antibodies are effective against viral and bacterial infections, while IgE antibodies are involved in the response to parasitic infections and in allergic reactions.

Regulation

The cytokine environment during an immune response determines the class of antibody produced. For example, the cytokine Interleukin-4 (IL-4) induces class switching to IgE and IgG1 in humans.

Clinical Significance

Defects in the process of class switching can lead to immunodeficiency disorders, such as Hyper-IgM syndrome, where patients produce normal levels of IgM antibodies but reduced levels of other classes of antibodies.

See Also

• B cell
• Antibody
• Cytokines
• Hyper-IgM syndrome