What are the similarities between IgG, IgM, IgE and IgD?

IgG, IgM, IgE and IgD are four of five classes of immunoglobulins. All are large, Y-shaped glycoprotein molecules composed of heavy chains and light chains. They are synthesized by activated plasma cells and are vital components of the humoral immune system. They all have the ability to recognize and bind to a specific epitope of a pathogenic antigen.