Which immunoglobulin class is commonly found as a pentamer in serum?

Which immunoglobulin class is commonly found as a pentamer in serum?

• A. IgA
• B. IgM
• C. IgG
• D. IgD

Answer: (B)

IgM is the immunoglobulin class that is commonly found as a pentamer in serum because it is produced as a pentameric molecule held together by a joining (J) chain. This pentameric structure gives it ten antigen-binding sites, which provides very high avidity for antigens and makes it especially effective at clumping red cells or pathogens (agglutination) and strongly activating the classical complement pathway right at the start of an immune response. In the early phase of humoral immunity, IgM is the first antibody produced before class switching to other isotypes. By contrast, IgA often appears as a dimer in secretions, while IgG and IgD are monomers.

IgM is the immunoglobulin class that is commonly found as a pentamer in serum because it is produced as a pentameric molecule held together by a joining (J) chain. This pentameric structure gives it ten antigen-binding sites, which provides very high avidity for antigens and makes it especially effective at clumping red cells or pathogens (agglutination) and strongly activating the classical complement pathway right at the start of an immune response. In the early phase of humoral immunity, IgM is the first antibody produced before class switching to other isotypes. By contrast, IgA often appears as a dimer in secretions, while IgG and IgD are monomers.