Blood Levels of Dendritic Cell Populations in Patients with Moderate to Severe Traumatic Brain Injury

Traumatic brain injury (TBI) leads to intracerebral inflammation involving resident microglial cells and astrocytes as well as invading peripheral dendritic cells (DCs), monocytes, and neutrophils. However, the profile of immune blood cells activated by TBI remains poorly defined. Several animal models showing invasion of circulating classical dendritic cells type 2 (cDC2s) to the traumatically injured brain have been found, resulting in exacerbated neurological outcomes. In TBI patients, increased levels of chemokine CCL2, attracting cDC2 cells, have been linked to poor recovery. In the present study, blood samples from healthy blood donors (n = 11) were compared with blood from TBI patients (n = 15) at day 1 and day 3 after admission for neurointensive care stored in two tested freezing media (eight patients using Cytodelics, seven patients using CryoStor CS10) for analyses by flow cytometry. Reference blood was collected from random healthy blood donors (7 with Cytodelics, 4 CryoStor CS10). Flow cytometry excluded T-cells, B-cells, and natural killer cells by a panel of CD3, CD19, CD20, and CD56 antibodies. To identify DCs and inflammatory monocytes, antibodies to CD11c, CD1c, CD141, HLA-DR, and CD14 labeled with specific fluorochromes were added to the thawed blood samples. Neutrophils were analyzed by separate runs of flow cytometry using a CD66b antibody. Despite some differences depending on the freezing medium used, the percentage of classical DCs type 2 (cDC2; CD14-, CD11c high, CD1c+) remained unchanged from healthy controls at day 1 after admission but increased significantly (p = 0.014) from day 1 until day 3 after TBI. In contrast, levels of classical DCs type 1, inflammatory monocyte-derived DCs, or neutrophils were not altered. Thus, our preliminary data, in addition to previous animal model data, suggest a role for circulating cDC2 cells contributing negatively to the pathophysiology of TBI.