Which immunoglobulin is primarily responsible for the secondary response to an antigen?

The primary role of immunoglobulin G (IgG) is crucial during the secondary immune response to an antigen. When the body is first exposed to an antigen, the immune system initially produces immunoglobulin M (IgM), which is effective in initial recognition and response. However, upon subsequent exposure to the same antigen, the immune system activates memory B cells that have been created during the primary response. These memory B cells can rapidly produce IgG, leading to a faster and more efficient immune response.

IgG has several important properties: it is the most abundant antibody in serum, it can cross the placenta providing passive immunity to the fetus, and it has a higher affinity for antigens compared to IgM. This affinity maturation and the ability to quickly mobilize upon re-exposure to an antigen characterize the secondary immune response, differentiating it from the primary response, which predominantly involves IgM production. Therefore, IgG is the key immunoglobulin responsible for the enhanced and sustained protection seen in secondary responses.