Thomas Kossmann

IL-10 levels in cerebrospinal fluid and serum of patients with severe traumatic brain injury: relationship to IL-6, TNF-α, TGF-β1 and blood–brain barrier function

Controlling the extent of inflammatory responses following brain injury may be beneficial since posttraumatic intracranial inflammation has been associated with adverse outcome. In order to elucidate the potential role of anti-inflammatory mediators, the production of interleukin-10 (IL-10) was monitored in paired cerebrospinal fluid (CSF) and serum of 28 patients with severe traumatic brain injury (TBI) and compared to control samples. The pattern of IL-10 was analyzed with respect to the patterns of IL-6, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) in both fluids during a time period of up to 22 days. In parallel, the function/dysfunction of the blood-brain barrier (BBB) was monitored using the CSF-/serum-albumin quotient (Q(A)) and compared to intrathecal cytokine levels. Mean IL-10 concentration in CSF was elevated in 26 out of 28 TBI patients (range: 1.3-41.7 pg/ml) compared to controls (cut-off: 1.06 pg/ml), whereas only seven patients had elevated mean IL-10 concentration in serum (range: 5.4-23 pg/ml; cut-off: 5.14 pg/ml). The time course of IL-10 was similar in both fluids, showing a peak during the first days and a second, lower rise in the second week. Intrathecal IL-10 synthesis is hypothesized since CSF-IL-10 levels exceeded serum-IL-10 levels in most of the patients, IL-10-index (CSF/serum-IL-10/QA) was elevated in 23 individuals, and elevation of CSF-IL-10 showed to be independent from severe BBB dysfunction. Neither CSF nor serum IL-10 values correlated with the dysfunction of the BBB. IL-10, IL-6 and TGF-beta1 showed similar patterns in CSF over time, whereas rises of TNF-alpha corresponded to declines of IL-10 levels. Our results suggest that IL-10 is predominantly induced intrathecally after severe TBI where it may downregulate inflammatory events following traumatic brain damage.

Interleukin-6 released in human cerebrospinal fluid following traumatic brain injury may trigger nerve growth factor production in astrocytes

Cytokines are involved in nerve regeneration by modulating the synthesis of neurotrophic factors. The role played by interleukin-6 (IL-6) in promoting nerve growth factor (NGF) after brain injury was investigated by monitoring the release of IL-6 and NGF in ventricular cerebrospinal fluid (CSF) of 22 patients with severe traumatic brain injuries. IL-6 was found in the CSF of all individuals and remained elevated for the whole study period. NGF appeared in the CSF if IL-6 levels reached high concentrations and was often detected simultaneously with or following an IL-6 peak. The amounts of NGF correlated with the severity of the injury, as indicated by the clinical outcome of the patients. The functional relationship of IL-6 and NGF was investigated utilizing cultured mouse astrocytes. The CSF of 8 patients containing IL-6 induced NGF production in astrocytes, whereas control CSF without IL-6 had no effect. The induction of NGF was inhibited up to 100% by adding anti-IL-6 antibodies. These results were corroborated when astrocytes were exposed to recombinant IL-6 at different concentrations resulting in NGF production. Thus, the production of IL-6 within the injured brain may likely contribute to the release of neurotrophic factors by astrocytes.

Cytokines and neuropathology

Inflammatory processes in the brain require the cooperation of immunocompetent cells and glial cells, which communicate by secreting bidirectional mediators. Resident cells within the nervous system can synthesize and secrete inflammatory cytokines, as well as neuropeptides, contributing to the response within the CNS to injury or immunological challenge. Although the mechanisms of cell activation and immune interaction are poorly understood, accumulating evidence implicates these pathways in neuropathogenesis, as described here by Sharon Wahl and colleagues. For example, in the acquired immune deficiency syndrome (AIDS), HIV-1-induced nervous system dysfunction and dementia are associated with the presence of infiltrating leukocytes and the release of inflammatory cytokines. Defining the pathways of cytokine dysregulation and neurotoxicity invoked by the infiltrating leukocytes, as well as the contribution of the neural cells themselves, may help to identify mechanisms of intervention in this and other debilitating CNS diseases.

Traumatic Brain Injury Increases β‐Amyloid Peptide 1‐42 in Cerebrospinal Fluid

Abstract: The β‐amyloid peptides, Aβ1‐42 and Aβ1‐40, were quantified in ventricular CSF taken daily for up to 3 weeks from six individuals with severe traumatic brain injury (TBI). There was considerable interindividual variability in the levels of Aβ peptides, but in general Aβ1‐42 levels equalled or exceeded those of Aβ1‐40. Averaging the daily totals of our trauma cohort revealed that the levels of Aβ1‐42 and Aβ1‐40 rose after injury, peaking in the first week and then declining toward control levels over the next 2 weeks. Aβ1‐42 levels were on average two to three times higher in the trauma cohort than in CSF from nontrauma samples. Compared with nontrauma samples, the Aβ1‐40/Aβ1‐42 ratio decreased about fivefold in the trauma patients, further indicative of increased Aβ1‐42 levels. The ratio remained low at all time points studied. No change was measured in the levels of β‐amyloid precursor protein during the same interval. These results suggest that Aβ1‐42 becomes elevated in the CSF after severe brain trauma.

sICAM-1 and TNF-? induce MIP-2 with distinct kinetics in astrocytes and brain microvascular endothelial cells

The dysfunction of the blood‐brain barrier (BBB) occurring after traumatic brain injury (TBI) is mediated by intracerebral neutrophil accumulation, chemokine release (e.g., interleukin (IL)‐8) and upregulation of adhesion molecules (e.g., intercellular adhesion molecule (ICAM)‐1). In patients with severe TBI, we previously found that elevated cerebrospinal fluid (CSF) IL‐8 and soluble (s)ICAM‐1 correlate with BBB dysfunction, and this prompted us to concomitantly monitor IL‐8, sICAM‐1 and their stimulator tumor necrosis factor (TNF)‐α in CSF. Potential mechanisms for upregulation of the IL‐8 analogue, murine macrophage inflammatory protein (MIP)‐2, and sICAM‐1 at the BBB were studied using cultured mouse astrocytes and brain microvascular endothelial cells (MVEC). In CSF of seven patients, IL‐8 and sICAM‐1 were elevated for 19 days after severe TBI, whereas TNF‐α exceeded normal values on 9 days. Stimulation of MVEC and astrocytes with TNF‐α simultaneously induced the release of MIP‐2 reaching saturation by 4–8 hr and of sICAM‐1 increasing continuously from 2–4 hr to 12 hr. Augmented sICAM‐1 production correlated with enhanced membrane‐bound (m)ICAM‐1 expression in both cell types (rs = 0.96 and 0.90, P < 0.0001), but was markedly higher in astrocytes. The release of sICAM‐1 was not influenced by IL‐8 or MIP‐2, although astrocytes and MVEC expressed the IL‐8/MIP‐2 receptor (CXCR‐2) as determined by FACS analysis. Instead, we found that sICAM‐1 strongly induced MIP‐2 secretion by both cell types with kinetics differing from those evoked by TNF‐α. If added together, sICAM‐1 and TNF‐α synergistically induced MIP‐2 production suggesting the involvement of two different pathways for MIP‐2 regulation. J. Neurosci. Res. 60:733–742, 2000.

Prolonged intrathecal release of soluble Fas following severe traumatic brain injury in humans

The mechanisms underlying cell death following traumatic brain injury (TBI) are not fully understood. Apoptosis is believed to be one mechanism contributing to a marked and prolonged neuronal cell loss following TBI. Recent data suggest a role for Fas (APO-1, CD95), a type I transmembrane receptor glycoprotein of the nerve growth factor/tumor necrosis factor superfamily, and its ligand (Fas ligand, FasL) in apoptotic events in the central nervous system. A truncated form of the Fas receptor, soluble Fas (sFas) may indicate activation of the Fas/FasL system and act as a negative feedback mechanism, thereby inhibiting Fas mediated apoptosis. Soluble Fas was measured in cerebrospinal fluid (CSF) and serum of 10 patients with severe TBI (GCS< or =8) for up to 15 days post-trauma. No sFas was detected in CSF samples from patients without neurological pathologies. Conversely, after TBI 118 out of 120 CSF samples showed elevated sFas concentrations ranging from 56 to 4327 mU/ml. Paired serum samples showed above normal (8.5 U/ml) sFas concentrations in 5 of 10 patients. Serum levels of sFas were always higher than CSF levels. However, there was no correlation between concentrations measured in CSF and in serum (r(2)=0.078, p=0.02), suggesting that the concentrations in the two compartments are independently regulated. Also, no correlation was found between sFas in CSF and blood brain barrier (BBB) dysfunction as assessed by the albumin CSF/serum quotient (Q(A)), and concentrations of the cytotoxic cytokine tumor necrosis factor-alpha in CSF, respectively. Furthermore, there was no correlation with two markers of immune activation (soluble interleukin-2 receptor and neopterin) in CSF. Maximal CSF levels of sFas correlated significantly (r(2)=0.8191, p<0.001) with the early peaks of neuron-specific enolase in CSF (a marker for neuronal cell destruction), indicating that activation of the Fas mediated pathway of apoptosis may be in part the direct result of the initial trauma. However, the prolonged elevation of sFas in CSF may be caused by the ongoing inflammatory response to trauma and delayed apoptotic cell death.

Upregulation of ICAM-1 and MCP-1 but not of MIP-2 and sensorimotor deficit in response to traumatic axonal injury in rats.

The pathophysiology of traumatic axonal injury (TAI) is only partially understood. In this study, we investigated the inflammatory response as well as the extent of neurological deficit in a rat model of traumatic brain injury (TBI). Forty‐two adult rats were subjected to moderate impact‐acceleration brain injury and their brains were analyzed immunohistochemically for ICAM‐1 expression and neutrophil infiltration from 1 hr up to 14 days after trauma. In addition, the chemotactic factors MIP‐2 and MCP‐1 were measured in brain homogenates by ELISA. For evaluating the neurological deficit, three sensorimotor tests were applied for the first time in this model. In the first 24 hr after trauma, the number of ICAM‐1 positive vessels increased up to 4‐fold in cortical and subcortical regions compared with sham operated controls (P < 0.05). Maximal ICAM‐1 expression (up to 8‐fold increase) was detected after 4 days (P < 0.001 vs. 24 hr), returning to control levels in all brain regions by 7 days after trauma. MCP‐1 was elevated between 4 hr and 16 hr post‐injury as compared with controls. In contrast, neither neutrophil infiltration nor elevation of MIP‐2, both events relevant in focal brain injury, could be detected. In all neurological tests, a significant deficit was observed in traumatized rats as compared with sham operated animals from Day 1 post‐injury (grasping reflex of the hindpaws: P < 0.001, vibrissae‐evoked forelimb placing: P = 0.002, lateral stepping: P = 0.037). In conclusion, after moderate impact acceleration brain injury ICAM‐1 upregulation has been demonstrated in the absence of neutrophil infiltration and is paralleled by a selective induction of chemokines, pointing out that individual and distinct inflammatory events occur after diffuse vs. focal TBI. J. Neurosci. Res. 63:438–446, 2001.

Inflammatory Response to Brain Injury

Historically, it was believed that the central nervous system (CNS) fails to mount an inflammatory response due to its protection from the systemic immune system mediated by the blood-brain barrier (BBB). However, in the last decades, participation of neuronal and glial cells in inflammatory events occurring in infectious, autoimmune and degenerative neuropathologies became increasingly evident (Morganti-Kossmann et al. 2000). With regard to traumatic brain injury (TBI), it has been reported in clinical (Bell et al. 1997; Morganti-Kossmann et al. 1997; Holmin et al. 1998) as well as experimental studies (Taupin et al. 1993; Shohami et al. 1994; Fan et al. 1995; Fan et al. 1996; Carlos et al. 1997; Hans et al. 1999; Csuka et al. 2000) that, despite the presence of the BBB, a profound inflammatory response occurs within the brain immediately following injury. It is nowadays accepted that 1) immune surveillance is present in the CNS, 2) an immune response can be induced within the brain, 3) most of the molecules and mechanisms modulating the inflammatory response are present and active within the brain and 4) bi-directional communication exists between the nervous and the immune systems.

Low T3 Syndrome in Head-Injured Patients is Associated with Prolonged Suppression of Markers of Cell-Mediated Immune Response

Purpose:To clarify the association between disturbed thyroid hormone metabolism (low T3 syndrome) and release of cytokines and markers of cell-mediated immune response.Material and Methods:Concentrations of cytokines as well as of thyroid hormones were determined in 32 patients suffering from severe traumatic brain injury: interleukin-( IL-)1, IL-6, IL-10, tumor necrosis factor, transforming growth factor-(TGF-)β, soluble interleukin-2 receptor (sIL-2R), neopterin, and β2-microglobulin (β2m) in serum and cerebrospinal fluid; triiodothyronine (T3), free T3, thyroxine (T4), free T4, thyrotropin, thyroxine-binding globulin, and albumin in serum. Additionally, clinical parameters were assessed: Glasgow Coma Score, CT scan, intracranial pressure, Glasgow Outcome Score, and occurrence of pneumonia.Results:Among 31 patients with a low T3 syndrome, those with additional low serum T4 levels (n = 13) showed a prolonged suppression of serum β2m, neopterin, and sIL-2R, and a higher secondary increase of serum β2m, neopterin, and TGF-β, as well as lower T3 levels (all p < 0.05). These patients also had a longer stay in the intensive care unit (34 ± 6 days vs. 22 ± 12 days; p = 0.008). Increased levels of β2m correlated with a preceding decrease of thyrotropin (cerebrospinal fluid: r = –0.53; p = 0.004; serum: r = –0.41; p = 0.029). Associations of thyroid hormone metabolism with either other cytokines or with clinical parameters were not detected.Conclusion:These results show that low T3 syndrome is a very common pathophysiological feature after severe traumatic brain injury. The association of a low T3 syndrome in combination with low serum T4 levels, with an altered time course of markers of cell-mediated immunity led the authors to hypothesize that a disturbed thyroid hormone metabolism may be interrelated with a prolonged cellular immune dysfunction after traumatic brain injury.