Class switching

Class Switching is a biological process that occurs in the immune system of vertebrates. It is also known as Isotype Switching or Immunoglobulin Class Switching.

Overview

Class switching is a 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. During this process, the constant-region portion of the antibody heavy chain is changed, but the variable region of the heavy chain stays the same. This means that class switching changes the Fc region of the antibody, and thus its biological properties, but does not affect antigen specificity.

Mechanism

The process of class switching is mediated by a specific type of DNA recombination known as class switch recombination (CSR). This process is initiated by activation-induced cytidine deaminase (AID), which deaminates cytosine residues in DNA to uracil. This leads to DNA cleavage, followed by recombination and ligation, resulting in the replacement of one constant region gene by another.

Function

The main function of class switching is to allow the immune system to respond flexibly to a range of different antigens. Different classes of antibodies (IgM, IgG, IgA, IgE) have different roles in the immune response, and class switching allows a B cell to produce the type of antibody that is most effective against a particular antigen.

Clinical Significance

Defects in class switching can lead to immunodeficiency disorders, such as Hyper-IgM syndrome, where B cells can only produce IgM antibodies. On the other hand, inappropriate or excessive class switching can contribute to autoimmune diseases, allergies, and other pathological conditions.

See Also

• Antibody
• B cell
• Immunoglobulin
• DNA recombination
• Hyper-IgM syndrome