Kinetics of T cell turnover following thymectomy

We develop a mathematical formula that provides the number of cells in an i solated population that have divided k times in n days (0 less than or equa l to k less than or equal to n). This differential cell division formula is applied to the kinetics of peripheral T cells in the diabetes-prone BB rat following thymectomy. These rats received daily intraperitoneal injections of the DNA precursor, bromodeoxyuridine (BrdUrd), over a period of 12-13 d ays. As the cells divided, they incorporated BrdUrd progressively into thei r DNA molecules, and the differential formula provides a close prediction o f the fraction of BrdUrd-positive T cells present each day during this 'pul se' phase. No further BrdUrd was administered after 13 days, and the dimini shing fraction of BrdUrd-positive cells was recorded for several more weeks . The differential cell division formula was capable of describing the rath er complex form of the retention curve as BrdUrd-tagged DNA molecules passe d to progeny cells during this 'chase' phase. We believe that this simple f ormula may be found generally useful in describing cell kinetic data in mit otically active cells.