Monocyte activation and distribution and the association with outcome in veno-arterial extracorporeal membrane oxygenation

Introduction: Veno-arterial extracorporeal membrane oxygenation may initiate an inflammatory reaction. Different subgroups of Monocytes have been described. Designed Ankyrin Repeat Protein "F7" and Single Chain Variable Fragment "MAN-1" are proteins that can specifically bind to the active conformation of the integrin Mac-1, expressed on leukocytes enabling the detection of activated monocytes. The aim was to investigate the heterogeneity and activation level of monocytes and their relation to mortality in VA-ECMO patients. Methods: VA-ECMO Patients were recruited from the intensive care units of the University Hospital in Freiburg, Germany. Blood was taken within the first 24 hours after ECMO implantation (day 0), 72 hours ± 12 hours after VA-ECMO initiation (day 3) and within 12 hours after explantation. Blood was also collected from healthy subjects. Baseline activation, stimulability and subgroup distribution of monocytes with flow cytometry were analyzed using the surface markers CD163, CD86, CX3CR1 and CD69 and the binding proteins F7 and MAN-1. The results in survivors were compared with those of non-survivors. The association of monocyte activation markers with mortality was determined by performing a simple logistic regression. Results: Twenty-two patients with VA-ECMO and 15 healthy controls were recruited. Eleven patients survived until discharge from the intensive care unit. Compared to controls, monocyte activation was significantly increased and the ability to be stimulated was reduced. After VA-ECMO explantation, the proportion of classical monocytes increase and the proportion of intermediate monocytes decreased. Compared to healthy controls, the absolute number of classical and intermediate monocytes was significantly increased. At day 0, baseline binding of F7 was significantly lower in non-survivors than in survivors. The area under the ROC curve associated with mortality on day 0 was 0.802. Conclusion: During VA-ECMO the distribution of monocyte subsets changes. Compared to healthy controls, absolute classical and intermediate monocyte counts are significantly increased. Monocytes from VA-ECMO patients showed signs of dysfunction, which could be detected with the binding protein F7. Since monocyte dysfunction detected by F7 was predictive of poor outcome, F7 may be used as a new diagnostic tool to guide therapy decisions in the future.