IgM is the first antibody generated in an immune response to an antigen. It is generally a pentamer with each of the five immunoglobulins linked together with disulfide bonds. In its pentamer form, it has a molecular mass of 970 kDa and 10 antigen binding sites (due to the large size of most antigens, not all binding sites can be filled simultaneously.  IgM antibodies account for approximately 5%-10% of all the antibody in the body.

Store the IgM antibody at 2-8°C (with azide) or aliquot and store at -20°C or colder (without azide).