Ige class change

In immunology, "class change" refers to a change of isotype in B lymphocytes.

Naive (immunologically not yet imprinted) B cells produce exclusively the immunoglobulins IgM and IgD. At the first contact with an antigen, the still naive B-cell will therefore only generate IgM antibodies. In the course of a necessary, effective immune response, different isotypes of the immunoglobulins (IgG, IgA, IgE) or their subclasses (IgG1-4; IgA1-2) are required. These are only created during the secondary (or memory) immune response. The class change takes place mainly in the germinal centres of the lymph nodes. In addition to the differences in isotypes, the secondary immune response is much more effective because the already existing memory B cells proliferate faster after reactivation and can differentiate into plasma cells.

The class change from IgM to e.g. IgG or IgE is irreversible, since certain DNA sequences are irreversibly lost. However, a class change from one isotype to another is possible. Between the genes for the heavy chains are switch (S) sequences with the consensus (GAGCT)n (GGGGT) where "n" is usually 2-5, but can also go up to 17. When the switch mechanism is activated by different cytokines and other cosignals, chromosomal recombination occurs.

Switching (e.g. to IgE) means that the DNA sections in between are cut out chromosomally. This results in a ring-shaped DNA product which is degraded. A B cell can switch several times, but never back. If a cell produces IgE, it cannot transfer back to IgG. The relevant DNA sections are no longer present.