A novel method to quantify the turnover and release of monocytes from the bone marrow using the thymidine analog 5'-bromo-2'-deoxyuridine

McDonald Research Laboratories and iCAPTURE Centre, University of British Columbia, Saint Paul's Hospital, Vancouver, British Columbia, Canada V6Z1Y6 Submitted 23 January 2003 ; accepted in final form 25 March 2003 The present study was designed to develop methods to study the production and release of monocytes from the bone marrow using the thymidine analog 5'-bromo-2'-deoxyuridine (BrdU). Dividing monocytes in bone marrow were labeled with BrdU (MO BrdU ), and their release into the blood and disappearance from the circulation were monitored using a double immunostaining method. The first MO BrdU appeared in the circulation 4 h after labeling with BrdU and peaked at 18 h when 34.3 ± 5.8% of monocytes were labeled. The calculated transit time of monocytes through bone marrow was 38.1 ± 3.1 h in control rabbits with a half-life ( T 1/2 ) of 12.7 h. Instillation of Streptococcus pneumoniae into the lung accelerated the release of monocytes from bone marrow (peak at 10 h) and shortened their bone marrow transit time (27.1 ± 1.8 vs. 22.6 ± 0.6, vehicle vs. pneumonia; P < 0.05). We conclude that this nonradioisotope method provides a novel way to monitor monocyte kinetics and confirmed previous reports that a focal pneumonia shortens monocyte marrow transit and increases their release into the circulation. leukocytes; transit time; half life; pneumonia; rabbits Address for reprint requests and other correspondence: S. F. van Eeden, McDonald Research Laboratory, Univ. of British Columbia, St. Paul's Hospital, 1081 Burrard St., Vancouver, BC, Canada V6Z1Y6 (E-mail: svaneeden{at}mrl.ubc.ca ).