Losing self-awareness

Waste is rife in the immune system, based on a report from Hedda Wardemann, Michel Nussenzweig (Rockefeller University, New York, NY), and colleagues. The group has determined that more than half of the human B cell antibody population is removed before maturation.

The removal is a consequence of antibody gene rearrangement—a random process that is certain to generate some autoreactive antibodies. Nussenzweig's group now shows just how often autoreactivity occurs by identifying autoreactive B cells at different stages of development. Between 55% and 75% of the antibodies made by early immature B cells react against self antigens. These potentially dangerous antibodies are removed from the repertoire at two checkpoints: the number of self-reactive antibody-producing B cells were halved from within the bone marrow and then halved again after entering the blood stream. Also,...