Longitudinal characterization of olfactomedin-4 expressing neutrophils in pediatric patients undergoing bone marrow transplantation.

Sepsis is an important cause of morbidity and mortality in pediatric patients. Increased expression of olfactomedin-4 (OLFM4), a glycoprotein contained within a subpopulation of neutrophils, has been associated with complicated course in sepsis. The factors that regulate OLFM4 expression are unknown. Here, we followed children undergoing bone marrow transplantation (BMT) to document the percentage of neutrophils that express OLFM4 over time. This population was selected because of the ability to observe nascent neutrophils following engraftment, perform frequent blood sampling, and the children are at high risk for clinical complications that may associate with changes in percentage of OLFM4+ neutrophils. We found a surprising degree of variability of OLFM4 expression between patients. In the weeks following initial neutrophil recovery we also saw great variability in OLFM4 expression within individual patients, indicating that multiple external factors may modify OLFM4 expression. We identified decreased expression of CD64 (a marker associated with response to infection), in OLFM4+ neutrophils. This is the first study to demonstrate fluctuation in OLFM4 expression within patients and provides insight into possible mechanisms for OLFM4 regulation in nascent neutrophils.