Pulmonary and systemic effects of mononuclear leukapheresis

Background and Objectives There is increasing evidence that monocytes play a key role in the pathogenesis of acute lung inflammation. Mononuclear cell (MNC) leukapheresis can be used to remove large numbers of monocytes from circulating blood; however, the detailed characteristics of monocyte subpopulations removed by MNC leukapheresis, and the biological effects on the lung, remain incompletely defined. Material and Methods Six healthy male volunteers underwent MNC leukapheresis of four total blood volumes. Blood was collected at 0, 2, 4, 6, 8 and 24 h; bronchoscopy with bronchoalveolar lavage (BAL) was performed at 8–9 h. Multiparameter flow cytometry was used to identify subpopulations of monocytes in blood and monocyte‐like cells in BAL fluid. Results A median of 5·57 × 10⁹ monocytes were retrieved. Blood monocyte counts indicated that the circulating blood monocyte pool was actively replenished during leukapheresis and subsequently contained a greater proportion of classical (CD14⁺⁺ CD16^?) monocytes. A particular subpopulation of monocyte‐like cells, reminiscent of classical monocytes, was also prominent in BAL fluid after leukapheresis. Conclusion Mononuclear cell leukapheresis was safe. The greater proportion of classical monocytes present in blood after MNC leukapheresis may be clinically significant. MNC leukapheresis also appears to affect the proportion of monocyte‐like cells in the lung; however, we found no evidence that leukapheresis has a clinically important pro‐inflammatory effect in the human lung.