Law enforcement, immune-style
How can our immune systems kill foreign invaders without harming ourselves? Those who suffer from autoimmune disease might say that their immune systems cannot distinguish between those two possibilities. The system seems to work properly for most of us, however, so how are things normally kept in check? A paper in the April issue of Nature Immunology (Vol. 2, Issue 4, 01 Apr 2001) sheds some light on how our autoreactive T cells (those that react with "self" molecules) are regulated.
For many autoimmune disorders, self-reactive T cells are a primary culprit. T cells mature in the thymus, where they are "educated". The maturation process identifies the harmful T cells that react with self molecules and orders them to self-destruct, whereas those that pose no risk are allowed to emerge and circulate throughout the body. Self-reactive T cells that escape notice do not get off scot-free, however, and recently scientists have become very excited about the possibility that a major form of policing is done by what are called regulatory T cells, which can turn off the harmful cells but don't kill them.
Andrew Caton's group from the Wistar Institute, Philadelphia, PA, USA, report that the regulatory T cells are also autoreactive. However, if, during their maturation in the thymus, a T cell binds to a self molecule instead of self-destructing, it is pushed into the "regulatory pathway". The fateful decision either to die or to enter the police force depends on the strength of the "self" interactions: they need to be strong but not too strong. By understanding the conditions that give rise to these cells, this research opens the way to use these cells to treat or prevent autoimmunity.
A News & Views was written on this paper by Shimon Sakaguchi of Kyoto University in Japan.
Andrew J. Caton
The Wistar Institute
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Institute of Frontier Medical Science
Dept Exptl Pathol
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(C) Nature Immunology press release.
Message posted by: Trevor M. D'Souza