E05 478 566 350 170 or Enzyme-Linked Immunosorbent Assays,E05 478 566 350 170 or Enzyme-Linked Immunosorbent Assays,Immunoglobulin M, or IgM for short, is a basic antibody that is produced by B cells. IgM is by far the physically largest antibody in the human circulatory system. It is the first antibody to appear in response to initial exposure to an antigen