The generation of new memories in the human immune system doesn't come at the cost of old ones, according to a study published on March 5th in the Journal of Experimental Medicine (www.jem.org).
Memory "killer" T cells are specialized cells that develop in response to specific infections and launch an accelerated attack if the specific pathogen returns. Experiments in mice have suggested that the development of new memory T cells causes the activation and subsequent demise of old ones—possibly because the immune system can only accommodate a certain number of these cells.
But the human immune system doesn't appear to be constrained by such space limitations. In a longitudinal study of college students, Kristin Hogquist and colleagues at the University of Minnesota Medical School found that acute infection with Epstein-Barr virus (the cause of infectious mononucleosis) triggers the activation of memory T cells specific for other viruses. But these cells did not multiply or die—their numbers remained the same over time.
Thus human memory T cell numbers simply build up over time. Whether this has a beneficial or detrimental effect on immune responses remains to be seen.
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The Journal of Experimental Medicine (JEM) is published by The Rockefeller University Press. All editorial decisions on manuscripts submitted are made by active scientists in conjunction with our in-house scientific editors. JEM content is posted to PubMed Central, where it is available to the public for free six months after publication. Authors retain copyright of their published works and third parties may reuse the content for non-commercial purposes under a creative commons license. For more information, please visit www.jem.org.
Odumade, O.A., et al. 2012. J. Exp. Med. doi:10.1084/jem.20112401
Journal
Journal of Experimental Medicine