IMMUNOLOGY

Detailed explanation-1: -Serum IgM exists as a pentamer in mammals and comprises approximately 10% of normal human serum Ig content. It predominates in primary immune responses to most antigens and is the most efficient complement-fixing immunoglobulin. IgM is also expressed on the plasma membrane of B-lymphocytes as a monomer.

Detailed explanation-2: -In contrast to IgG molecules that contain one Fc domain, pentameric IgM has five different Fc domains on the same molecule, facilitating rapid complement activation when a single IgM molecule recognizes a pathogen.

Detailed explanation-3: -IgM is the first antibody built during an immune response. It is responsible for agglutination and cyto-lytic reactions since in theory, its pentameric structure gives it 10 free antigen-binding sites as well as it possesses a high avidity.

Detailed explanation-4: -Soluble immunoglobulin M (IgM) forms a pentamer containing a joining (J) chain polypeptide. While IgM pentamer has various immune functions, it also behaves as a carrier of circulating apoptosis inhibitor of macrophage (AIM; also called CD5L) protein that facilitates repair during different diseases.