Gossel et al. used two experimental approaches to study the dynamics of memory T cells in mice. (A) To quantify the influx of naive T cells into the pool of existing memory T cells, they used the drug busulfan to selectively kill hematopoietic stem cells (HSC) in the bone marrow of CD45.1+ mice (red arrow), and then added new cells derived from bone marrow of CD45.2+ mice (green arrow). Naive T cells (light blue bubble) replaced around 10% of central memory T cells (CM) and about 6% of effector memory T cells (EM) per week (blue arrows). About half of the resident memory T-cell population was never replaced. (B) In a second experiment, the DNA of memory T cells was labeled with the marker BrdU to measure how rapidly cells in different memory T-cell subpopulations divide and die. By measuring the marker Ki67 (purple arrow), they could classify CM and EM cells into recently divided (Ki67+) and not recently divided (Ki67-) cells. Both the CM and the EM pools contained cells with fast and slow dynamics: the short-lived cells lived around three days and six days, respectively, while the long-lived cells lived for around six weeks in both subpopulations. (C) In the future, it might be useful to combine these two approaches to compare the cell division and death of recently recruited (CD45.2+) and pre-existing memory T cells (CD45.1+).
© 2007, Seans Potato Business, Wikimedia Commons, Creative Commons Attribution-Share Alike 3.0 Unported. Mouse used in Figure 1 parts A-C is reproduced with permission from Seans Potato Business.