Most monoclonal antibodies used in therapy target which class of immunoglobulins?

• A. IgG
• B. IgA
• C. IgM
• D. IgE

Answer: (A)

The key idea is that therapeutic monoclonal antibodies are built as IgG. This class stays in the bloodstream for a relatively long time and has an Fc region that can engage the immune system to attack targets. The Fc portion of IgG can bind Fc receptors on natural killer cells and macrophages to drive antibody-dependent cellular cytotoxicity and phagocytosis, and it can activate complement to enhance cell killing. These features, plus the ability to humanize or chimerize IgG molecules for safer, longer-lasting therapy, make IgG the most practical and effective choice for systemic monoclonal therapies. Other immunoglobulin classes don’t fit as well: IgA is mainly secreted at mucosal surfaces and often exists as dimers, limiting systemic use; IgM is a large pentamer that hampers tissue penetration and has different pharmacokinetics; IgE is tied to allergic responses and would pose significant safety risks.