What does IgM do?

• A. Eliminates pathogens early before IgG is produced.
• B. Primarily mediates allergic reactions.
• C. Crosses the placenta to provide fetal immunity.
• D. Directly neutralizes toxins.

Answer: (A)

IgM provides an early, first-line antibody response in infection. Its pentameric structure lets it bind multiple sites on a pathogen at once, promoting strong agglutination and robust activation of the classical complement pathway. This combination yields rapid pathogen elimination before the slower, more specific IgG response is generated.

That’s why the statement about eliminating pathogens early before IgG is produced best captures IgM’s primary role. IgE is the mediator of allergic reactions, IgG crosses the placenta to give fetal immunity, and while antibodies can neutralize toxins, the hallmark function of IgM in initial defense is rapid pathogen clearance through agglutination and complement activation.