Which immunoglobulin appears in highest titer in the secondary immune response?

In the context of the secondary immune response, IgG is the immunoglobulin that appears in the highest titer. During this phase, the immune system has already been exposed to an antigen and has developed memory cells specific to that antigen. Upon re-exposure, these memory B cells rapidly differentiate into plasma cells and produce large amounts of IgG.

IgG plays a vital role in providing long-term immunity and is the predominant antibody in the blood during an immune response to a previously encountered pathogen. Its structure allows it to effectively neutralize toxins, opsonize pathogens for phagocytosis, and activate the complement system, which enhances the immune response.

In contrast, IgM is typically the first antibody produced during a primary immune response. Although it can also be produced in response to a secondary exposure, it does not reach the same high titers as IgG. IgA is primarily involved in mucosal immunity, found in secretions such as saliva and mucus, and is not the predominant immunoglobulin in the bloodstream during the secondary response. IgE is associated with allergic reactions and responses to parasitic infections, rather than being the main player in secondary immune responses.

Thus, IgG is the immunoglobulin that reaches the highest levels