ANATOMY

Detailed explanation-1: -IgM is the primary antibody produced during an initial antigen challenge. Yet, upon subsequent antigen exposure, follicular B cells undergo isotype switching, resulting in IgG, IgG, IgE, or IgA production.

Detailed explanation-2: -IgM is the strongest inducer of classical complement activation; a single bound IgM results in a conformational change from a planar to a stable molecule, exposing a C1q-binding site within the constant (Fc) region of the Ab.

Detailed explanation-3: -It is well known that both IgG and IgM can activate complement via the classical pathway by binding of C1q to the Fc regions of these immunoglobulins. Recent advances have shown that also IgA is capable of activating the complement system.

Detailed explanation-4: -IgM not only serves as the first line of host defense against infections but also plays an important role in immune regulation and immunological tolerance. For many years, IgM is thought to function by binding to antigen and activating complement system.

Detailed explanation-5: -IgM is the first antibody produced in primary immune response.