Serum IgM is a pentameric or hexameric macro-immunoglobulin that serves as the first-line defense in humoral immunity. Constituting 1.2–4.0 mg/mL in plasma, it features 10–12 antigen-binding sites, enabling high-avidity interactions with pathogens, particularly non-protein antigens like microbial carbohydrates and lipids. As the earliest antibody produced during infection and the primary immunoglobulin in neonates, IgM activates the classical complement pathway through C1 binding, promoting opsonization and pathogen lysis. Its inability to cross the placenta makes elevated neonatal IgM a marker for intrauterine infections.
Common research uses
IgM plays dual roles in autoimmune pathology. While natural IgM aids homeostasis by clearing cellular debris, autoreactive IgM drives diseases like cold agglutinin disease and idiopathic thrombocytopenic purpura through erythrocyte or platelet targeting 4. Deficiencies manifest in Wiskott-Aldrich syndrome (linked to thrombocytopenia and recurrent infections) and Hyper IgM syndromes, characterized by impaired class-switching and susceptibility to Pneumocystis pneumonia, cryptosporidiosis, and malignancies. Clinically, IgM serves diagnostic and therapeutic purposes. It indicates recent infections through serological testing and helps identify autoimmune conditions via autoantibody detection. Intravenous immunoglobulin (IVIG) preparations containing IgM are used for immune thrombocytopenic purpura and Guillain-Barré syndrome, leveraging IgM’s immunomodulatory properties.
Common uses include ELISA standards, IVD Assay standards, calibrators and controls, therapeutics research, immune system research.
Extinction Coefficient (E) = 1.18, 0.1% at 280nm, 1cm
