Immunoglobulin M

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 antigen. The spleen is the major site of specific IgM production.

Read more about Immunoglobulin M:  Structure and Function, Expression, Clinical Significance, Other Points