Which antibody serves as the main component of the secondary immune response?

In the immune system, the secondary immune response refers to the body's reaction upon re-exposure to a pathogen, or more specifically, to an antigen that it has previously encountered. The predominant antibody involved in this response is immunoglobulin G (IgG).

When the body first encounters an antigen, it produces IgM, which is the first antibody to respond. However, upon subsequent exposures to the same antigen, the immune response is more rapid and robust, primarily due to the memory B cells generated during the initial response. These memory cells differentiate into plasma cells that produce IgG antibodies, which are more effective at neutralizing pathogens.

IgG has a higher affinity for antigens compared to IgM and also has a longer half-life, making it the most abundant antibody in the serum during a later exposure. Its ability to cross the placenta provides passive immunity to the fetus, highlighting its importance in the secondary immune response. This capability of IgG, along with its role in opsonization, complement activation, and neutralization of toxins and viruses, underscores why it serves as the main component in defending against previously encountered pathogens.