The big mess at the middle is an IgM pentamer, which just means five IgM antibodies bound together into an immunological ninja star. IgM is usually the first antibody to respond to an infection. The reason you can be tested for Lyme disease and they can tell the difference between an active infection and a past infection is that the IgM will be present if your body is still fighting in its initial encounter with the bug, while the IgG antibodies will persist for life, hanging around ready to multiply if you're ever re-infected.
"I'm pretty certain that cake doesn't have much effect on the immune system, but it sure made us happy."
Antijenic Drift: Antibody Cake!
Source: Antijenic Drift
Image credits: Jen
Art and Science of Laboratory Medicine