Class switching

Immunoglobulin class switching (or isotype switching or Isotypic Commutation) is a biological mechanism that changes an antibody from one class to another, for example, from an isotype called IgM to an isotype called 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. Since the variable region does not change, class switching does not effect the antigens that are bound by the antibody. Instead, the antibody retains avidity for the same antigens, but can interact with different effector molecules.
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The process by which a IgM or IgD producing B lymphocyte switches to produce one of the secondary immunoglobulins (IgG, IgA or IgE) with the same antigen binding specificity.