Which antibody is the largest?

IgM is recognized as the largest antibody in terms of structure and molecular weight. This antibody is composed of five basic units (monomers) that are joined together, forming a pentamer shape. This unique structure allows IgM to effectively bind to multiple antigens at once, making it particularly efficient in agglutination and initiating the immune response.

In contrast, IgG is monomeric and smaller, while IgA can exist in both monomeric and dimeric forms, depending on its location (serum vs. secretions). IgE is also a monomer but is the least abundant antibody in the serum. The complex structure of IgM contributes not only to its size but also to its primary role in the early stages of an immune response, especially in infections, where it is one of the first antibodies produced.