Professional memory CD4+ T lymphocytes preferentially reside and rest in the bone marrow

CD4+ T lymphocytes are key to immunological memory, but little is known about the lifestyle of memory CD4+ T lymphocytes. We showed that in the memory phase of specific immune responses to antigens, most of the memory CD4+ T lymphocytes relocated into the bone marrow (BM) within 3-8 weeks after their generation, a process involving integrin a2. Antigen-specific memory CD4+ T lymphocytes expressed Ly-6C to a high degree, unlike most splenic CD44hiCD62L- CD4+ T lymphocytes. In adult mice, more than 80% of Ly-6Chi CD44hiCD62L- memory CD4+ T lymphocytes were in the BM. In the BM, they are located next to IL-7-expressing VCAM-1+ stroma cells, and were in a resting state. Upon challenge with antigen, they rapidly expressed cytokines and CD154 and induced the production of high-affinity antibodies, indicating their functional activity in vivo and marking them as professional memory T helper cells

6