Mouse immunoglobulin M （IgM） is a crucial component of the humoral immune system and is the first antibody produced by B-cells in response to an antigenic challenge. It exists in two forms: a pentameric （19S） form found in serum and a monomeric （8S） form on the surface of lymphocytes. The IgM pentamer, which is the predominant form in circulation, consists of five monomeric units and has a molecular weight of approximately 900 kDa, while the hexameric form has a molecular weight of about 1050 kDa. Each monomer of IgM is composed of two heavy chains and two light chains, with the heavy chain having four constant domains （CH1-CH4） and the light chain having one constant domain （CL）. The CH4 domain facilitates oligomerization, leading to the formation of penta- or hexamers, and these oligomers are covalently linked via disulfide bonds, resembling a snowflake structure. A joining （J） chain, a 15 kDa polypeptide, is essential for the secretion of IgM into mucosal areas.