CD16dimCD64+ granulocytes are of interest in the diagnosis of ventilator associated pneumonia in neurological intensive care unit patients

Background: The diagnosis of ventilator-associated pneumonia (VAP) is often challenging for front-line clinicians. During bacterial infection, the immune response and cytokine production can lead to emergency haematopoiesis with the release of immature granulocytes (IG). This cell population can be identified by flow cytometry using a combination of cell surface markers. We investigated whether daily monitoring of IG in peripheral blood could be associated with VAP in neurological intensive care unit (ICU) patients. Methods: This prospective, single-centre study included immunocompetent patients under invasive mechanical ventilation due to severe head injury or stroke. The expression of several surface markers (cluster of differentiation 10 [CD10], CD64, CD15, CD16) on granulocytes and plasma concentrations of 10 cytokines (interferon-γ [IFN-γ] interleukin 6 [IL-6], tumour necrosis factor-alpha [TNF-α], granulocyte-macrophage colony-stimulating factor [GM-CSF], IFN-γ-inducible protein 10 [IP-10], chemokine 2 [CCL-2], granulocyte colony-stimulating factor [G-CSF], IL-1 rα, C-X-C motif chemokine 8 [CXCL-8] and IL-10) were monitored daily during the first week of ICU stay. Independent physicians blinded to the flow cytometry results determined the date of potential pulmonary infectious events and classified them as VAP or ventilator-associated tracheobronchitis (VAT). Results: Forty patients were enrolled (mean age: 58 ± 16 years; mean Glasgow coma scale: 8 ± 4). Of them, 19 patients (47.5%) presented a pulmonary infectious event, which was adjudicated as a VAP in 6 patients and as a VAT in the 13 other patients. In the patients without pulmonary infectious events, the mean proportion of CD16 dim CD64 + IG between Day-0 and Day-7 was 1.05% ± 2.18%, with no significant variation over time. Similar results were obtained in patients who developed VAT (1.00% ± 1.78%). In contrast, patients who developed VAP exhibited higher proportions of CD16 dim CD64 + IG, which reached 6.86% ± 13.87% on the day of VAP diagnosis, with a significant increase exceeding 20% on the day of VAP diagnosis in 4 of them (67%). Among the granulocyte surface markers studied, only CD16 and CD64 expression levels changed at the time of VAP diagnosis. A peak of IL-6 > 1000 ng/L and of G-CSF > 160 ng/L was evidenced on the day of VAP diagnosis. Conclusion: In neurological ICU patients, flow cytometry analysis of granulocyte populations identified a subset of IG CD16 dim CD64 + , which temporally peaked on the day of VAP diagnosis, whereas VAT was not associated with any change.