Cardiopulmonary Bypass Induces Recruitment of Bone Marrow-Derived Leukocytes to the Lungs in Monkeys

BACKGROUND:

A bone marrow (BM) response induced by cardiopulmonary bypass (CPB) as a systemic inflammatory reaction has previously been postulated but not clarified. Newly released polymorphonuclear leukocytes (PMNs) and monocytes from the BM are known to be immature, indicating their greater potential to damage tissue. The present study aimed to examine the kinetics of BM-derived leukocytes associated with CPB in a nonhuman primate model.

METHODS:

Normothermic CPB was performed in cynomolgus monkeys for 2 hours through a median sternotomy. Leukocyte precursors were labeled in the BM of the monkeys in vivo by an intravenous injection of 5-bromo-2′-deoxyuridine (BrdU), and their release into the circulation and recruitment to the lungs after operation with or without CPB (control group) were monitored over time by flow cytometry.

RESULTS:

In normal-state monkeys, the calculated transit time of BrdU-labeled PMNs (PMN(BrdU)) through the BM was 143.6 ± 4.5 hours and that of monocytes was 100.9 ± 7.6 hours. CPB caused a rapid release of PMNs and monocytes from the BM, shortened their transit through the BM to 92.0 ± 4.1 and 60.3 ± 2.9 hours, respectively, and further induced their increased appearance in the alveolar spaces, with a significant increase in both interleukin (IL)-6 and IL-8 levels in the bronchoalveolar lavage fluid (BALF) 24 hours after CPB.

CONCLUSIONS:

CPB accelerated the release of PMNs and monocytes from the BM and their recruitment to the lungs in our monkey model, indicating that this model is relevant for monitoring the kinetics of BM-derived leukocytes in humans.