In order to cause disease, at least 8,000 to 10,000 spores need to lodge deep in the lungs, in
the tiniest air sacs known as alveoli. This warm environment stimulates the bacterium to
emerge from its protective spore. As each bacterium reproduces it releases toxins, which
eventually spread throughout the body and destroy tissue and organs. One of the toxins,
called protective antigen, attaches to a receptor found on most cells. Once seven of these
antigens find a cell, they latch together to form a ring with a hold in the middle. Then one
of the other toxins produced by the bacterium—either a killing or swelling toxin—plugs the
hole and puts the cell immune system into overdrive to the point where tissue destruction
starts.