The cellular response capacity (CRC) as a novel immunomonitoring approach in sepsis

Background: Early recognition of sepsis remains difficult in clinical practice because conventional humoral biomarkers such as C-reactive protein, procalcitonin, and interleukin-6 (IL-6) exhibit unfavorable, slow-release kinetics and rise hours after the onset of infection. Flow cytometry enables upstream, cell-based immunomonitoring, but its clinical use is restricted by poor standardization of fluorescence measurements. In this study, the neutrophil cellular response capacity (CRC) was developed and evaluated as a standardized approach for rapid assessment of systemic inflammation in bacteremia and sepsis. Methods: The CRC is based on a flow cytometry-based framework that defines a stable maximal stimulation reference point for neutrophil granulocytes. The CRC was evaluated in a human ex vivo whole blood bacteremia model with graded exposure to Escherichia coli and compared with humoral inflammatory markers. Next, the CRC was assessed in a prospective intensive care unit sepsis cohort. Moreover, preliminary validation was performed in an independent sepsis cohort and in patients undergoing cardiac surgery. Results: In the bacteremia model, the CRC of neutrophil markers CD10, CD11b, and CD66b increased in a dose-dependent manner with increasing bacterial burden and detected inflammation at lower pathogen burdens than IL-6 and other humoral mediators, with a superior area under the receiver operating characteristic curve. In clinical sepsis, the CRC discriminated patients from age- and sex-matched healthy volunteers, with the CRC of CD11b showing the highest diagnostic performance. CRC values increased over time in patients with sepsis, consistent with immunological recovery. The maximal stimulation reference point for CD11b remained stable across inflammatory states, cohorts, and instruments. In addition, the CRC more precisely captured the onset and resolution of surgery-induced inflammation than conventional biomarkers. Conclusions: The CRC provides a rapid, standardized, and robust cell-based immunomonitoring tool that outperforms traditional humoral markers in experimental bacteremia and reliably identifies sepsis in clinical cohorts, strongly supporting its use as a novel biomarker for earlier, more precise sepsis diagnosis and monitoring.