Properties of immunoglobulin M

The main characteristics of the Immunoglobulin M (IgM) are as follow:  

- IgM is the first type of immunoglobulin produced by the human fetus

- High molecular weight (900,000 Da)

- Concentration in serum: 0.5 - 2 mg/mL.

- IgMs appear in the response to initial exposure to an antigen (primary response)

Explanation:

Immunoglobulin M (IgM) antibodies are high molecular weight proteins produced by the immune system in vertebrates. These antibodies are part of the adaptive humoral immune response. IgM, like IgA, are produced early in the infection. IgM antibodies act by recognizing and binding to specific antigens such as, for example, bacteria, viruses, fungi, parasites, etc. There exist two classes of IgM depending on the number of basic units: monomeric IgM and pentameric IgM. The monomeric form is expressed as a membrane-bound antibody on the surface of B lymphocytes, while pentameric IgM is produced by plasma cells.