IgM Human

Immunoglobulin M (IgM) is a basic antibody produced by B cells. IgM is the first antibody to emerge in response to initial exposure to an antigen. IgM antibodies are found in the blood and lymph fluid and are the third most widespread serum Ig. Immunoglobulin M (IgM), being the 3rd most widespread serum Ig and exists in two forms- mostly as a pentamer (970kDa) but also as a hexamer. The pentameric IgM has 10 binding sites since each monomer has two antigen binding sites. Due to distance constraints in the hexameric complex, the J chain is found in pentameric IgM but not in the hexameric form. IgM antibodies, which appear early in the course of an infection, typically reappear to a smaller extent after additional exposure. IgM, as opposed to IgG antibodies, do not pass across the human placenta. These properties of IgM make it suitable for the diagnosis of infectious diseases.