What happens to IgM levels during the secondary immune response?

During the secondary immune response, IgM levels exhibit a delayed spike due to the nature of how the immune system responds to previously encountered antigens. When the body is first exposed to a pathogen, IgM is the first antibody to be produced, indicating an initial immune response. Upon re-exposure to the same antigen, the immune system recognizes it more quickly and efficiently, leading to a stronger and faster response.

While IgG levels rise promptly during the secondary response, IgM is also produced but tends to do so with a slight delay compared to IgG. This delayed increase occurs because the memory B cells activated during the first exposure preferentially produce IgG in response to the re-infection, while IgM production follows shortly after due to the ongoing immune activation.

Thus, the presence of IgM during the secondary immune response does not disappear or decrease immediately; it instead spikes after a delay, reflecting the ongoing immune activity and overall enhancement of the immune response due to the memory component.