Which of the following immunoglobulins is known to facilitate opsonization?

Opsonization is a process that enhances the ability of antibodies and phagocytic cells to identify and clear pathogens such as bacteria and viruses from the body. Among the immunoglobulins, IgG is the most effective at facilitating opsonization. It binds to pathogens and marks them for destruction by phagocytes, such as neutrophils and macrophages. The Fc region of IgG can interact with specific receptors on the surface of these immune cells, promoting their engulfment and subsequent degradation of the pathogen.

In contrast, IgA primarily functions in mucosal immunity and is found in secretions like saliva, tears, and breast milk, where it helps to protect mucosal surfaces. IgM, while involved in the initial immune response and effective at forming immune complexes, is less efficient than IgG in opsonization. IgD is mainly a receptor on B cells and has a less understood role in the immune response, not being primarily associated with opsonization.

The specificity of IgG for opsonization makes it a key player in adaptive immunity, especially in responses to extracellular pathogens.