Antibodies, as noted, are protein molecules. They will either leave the body in secretions or be broken down by enzymes that degrade proteins in the body. The average life span of most antibody molecules is roughly a few weeks. Continued antigen stimulation is necessary to continue the antibody response, and as the antigen disappears, the stimulation disappears. The antibodies produced as a result of the initial stimulation remain in the bloodstream for a long period of time, with about half the quantity disappearing after a few weeks and half the remaining disappearing after another few weeks, and so forth. In many cases, the antibody level is sufficient to sustain an individual for the remainder of his or her life, especially after recovery from disease.
