New findings overturn a major model of where immune memory is stored. Rather than circulating throughout the body, as researchers had thought, memory T-cells actually reside in a comfortable niche in the bone marrow waiting for the next chance to fight infection, according to a new article published online in Immunity today (May 7th). Immunologists have long believed that memory cells come from activated effector T cells that have resigned their ability to fight, and simply remain in circulation until they are re-activated a second time by the same pathogen they initially attacked. Researchers have now found that rather than remaining in the circulation as previously thought, the majority return to the bone marrow, 80% of them are found here. These cells remained there for up to 134 days — the length of time the researchers tested.
To make sure the cells they detected in the bone marrow were “true” memory cells, the researchers characterised their surface molecules and tested them for the characteristics of memory cells: lack of proliferation, decreased gene expression, and the ability to reactivate upon re-infection with the same pathogen they had initially encountered. The cells in the bone marrow passed all three tests. The remaining 20% of cells not in the bone marrow probably belonged to a subset of T-memory cells that had been reactivated or were reacting to chronic infection.
Tokoyoda K, Zehentmeier S, Hegazy AN, Albrecht I, Grün JR, Löhning M, Radbruch Professional memory CD4+ T lymphocytes preferentially reside and rest in the bone marrow. A Immunity. 2009 May;30(5):721-30. Epub 2009 May 7. View Abstract
