Circulating CD10⁻/CD16^low neutrophils provide a quantitative index of active bone marrow neutrophil release

Abstract

Summary Circulating neutrophil phenotype and function are altered during neutrophilia associated with acute inflammatory states, however, the contribution of bone marrow neutrophil release to these changes has been difficult to quantify in humans. Accelerated release of neutrophils, with potentially distinct attributes, from the bone marrow and their dilution within the circulating pool may produce these apparent changes. Unfortunately selective analysis of these newly emergent neutrophils is difficult given their morphologic similarity to those already in the circulation and the coincident effect of soluble inflammatory mediators on circulating neutrophil phenotype and function. Using whole blood flow cytometry and cardiac surgery as an inflammatory stimulus, we demonstrate the emergence of a unique subpopulation of circulating neutrophils characterised as CD10−/CD16low, indicative of active bone marrow neutrophil release peri‐operatively. CD10−/CD16low neutrophils emerge at the same operative stages as band forms and a left shift, yet represent over 40% of circulating neutrophils postoperatively, and generate a greater stimulus‐induced [Ca2+]i flux than their CD10+ counterparts. We conclude that CD10−/CD16low neutrophils represent a significant proportion of the circulating pool after cardiac surgery and that bone marrow release, a major contributor to neutrophilia, influences the phenotype and functional activity of circulating neutrophils following this acute inflammatory stimulus.

A kinetic model of bone marrow neutrophil production that characterizes late phenotypic maturation

“…Ϫ under basal conditions in this study and others (24,30,35). In contrast to morphological maturational changes that occur on a time scale of days, our results suggest that phenotypic changes occur at a more rapid rate, since acquisition of CD10 expression was evident on an hourly basis.…”

“…However, as exemplified in previous studies (35), the CD10 Ϫ /CD16 low phenotype identifies greater numbers of phenotypically immature neutrophils than does cellular morphology alone. The temporal profile of phenotypic maturation may therefore provide a more detailed and accurate indicator of the rate at which mature phenotypic characteristics are acquired.…”

“…During ECC, active bone marrow neutrophil release is reportedly suppressed by hypothermia but stimulated by systemic rewarming (38,41) and may be further augmented with myocardial reperfusion (25,35). Total circulating neutrophil numbers increased during procedural (P ϭ 0.03), warming (P Ͻ 0.0001), and weaning (P ϭ 0.06) phases of ECC (Fig.…”

“…Cardiac surgery with hypothermic ECC was performed through a median sternotomy under general anesthesia as previously described (35). After administration of 400 U/kg unfractionated porcine heparin (Pharmacia), ECC was established.…”

“…We (35) and others (24,32) have demonstrated that an increased proportion of circulating neutrophils exhibit a CD10 Ϫ phenotype, in association with low CD16 expression (CD10 Ϫ /CD16 low ) (35) during active bone marrow neutrophil recruitment. Neutrophil CD10 expression is functionally significant, since this zinc metalloprotease (neutral endopeptidase 3.4.24.11) cleaves and inactivates multiple proinflammatory, vasoactive, and neuropeptides (6,18,39).…”