Markers for Cell-Mediated Immune Response Are Elevated in Cerebrospinal Fluid and Serum After Severe Traumatic Brain Injury in Humans

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Abstract
The brain is believed to be an immunologically privileged organ, sheltered from the systemic immunological defense by the blood-brain barrier (BBB). However, there is increasing evidence for a marked inflammatory response in the brain after traumatic brain injury (TBI). Markers for cellular immune activation, neopterin, β2-microglobulin (β2M), and soluble interleukin-2 receptor (sIL-2R), were measured for up to 3 weeks in cerebrospinal fluid (CSF) and serum of 41 patients with severe TBI in order to elucidate the time course and the origin of the cellular immune response following TBI. Neopterin gradually increased during the first posttraumatic week in both CSF and serum. Concentrations in CSF were generally higher than in serum, suggesting intrathecal release of this marker. β2M showed similar kinetics but with higher serum than CSF concentrations. Nonetheless, intrathecal release as assessed by the β2M index could be postulated for most of the patients. The mean levels of sIL-2R in both CSF and serum were elevated during the whole study period, serum concentrations being up to 2 × 104 times higher than in CSF. No significant intrathecal production of sIL-2R could be detected. The present data shows that severe TBI leads to a marked cell-mediated immune response within the brain and in the systemic circulation. In the intrathecal compartment the activated cells appear to be predominantly of the macrophage/microglia lineage, while the immune activation in the systemic circulation seems to involve mainly T-lymphocytes.