Which immunoglobulin is produced first in response to a new infection as part of the humoral immune response?

IgM is the first immunoglobulin class produced by B cells during the primary humoral immune response. It is the largest antibody and is produced within the first days of infection. IgM is an effective activator of complement and provides immediate defense before class switching occurs. After class switching, IgG becomes the predominant antibody in secondary immune responses and provides long-term immunity. IgA is primarily secreted at mucosal surfaces. IgE mediates allergic reactions and antiparasitic responses.