The neuroinflammatory response in humans after traumatic brain injury.

AIMS: Traumatic brain injury is a significant cause of morbidity and mortality worldwide. An epidemiological association between head injury and long-term cognitive decline has been described for many years and recent clinical studies have highlighted functional impairment within 12 months of a mild head injury. In addition chronic traumatic encephalopathy is a recently described condition in cases of repetitive head injury. There are shared mechanisms between traumatic brain injury and Alzheimer's disease, and it has been hypothesized that neuroinflammation, in the form of microglial activation, may be a mechanism underlying chronic neurodegenerative processes after traumatic brain injury. METHODS: This study assessed the microglial reaction after head injury in a range of ages and survival periods, from <24-h survival through to 47-year survival. Immunohistochemistry for reactive microglia (CD68 and CR3/43) was performed on human autopsy brain tissue and assessed 'blind' by quantitative image analysis. Head injury cases were compared with age matched controls, and within the traumatic brain injury group cases with diffuse traumatic axonal injury were compared with cases without diffuse traumatic axonal injury. RESULTS: A major finding was a neuroinflammatory response that develops within the first week and persists for several months after traumatic brain injury, but has returned to control levels after several years. In cases with diffuse traumatic axonal injury the microglial reaction is particularly pronounced in the white matter. CONCLUSIONS: These results demonstrate that prolonged microglial activation is a feature of traumatic brain injury, but that the neuroinflammatory response returns to control levels after several years.

Cerebral amyloid angiopathy in traumatic brain injury: association with apolipoprotein E genotype.

OBJECTIVE: In view of the association of the apolipoprotein E (APOE) epsilon 4 allele with poor outcome after traumatic brain injury we determined the frequency of cerebral amyloid angiopathy (CAA) and the extent of haemorrhagic pathology in relation to APOE genotype in an autopsy series of 88 head injured cases. METHODS: Tissue sections from the frontal and temporal lobes were immunostained for amyloid-beta peptide (A beta) and stained for Congo red to identify vascular amyloid pathology. A semiquantitative assessment of contusions, the total contusion index, was used to estimate the severity of the haemorrhagic pathology. APOE genotypes were determined by polymerase chain reaction of genomic DNA extracted from paraffin embedded tissue sections. RESULTS: CAA was present in 7/40 (18%) epsilon 4 carriers compared with 1/48 (2%) non-epsilon 4 carriers (p = 0.021, 95% confidence interval (CI) for difference in proportions with CAA 3% to 29%) with 6/40 (4 with CAA) epsilon 4 carriers being homozygotes. Thus the risk of having CAA for epsilon 4 carriers was 8.4 times that for the non-epsilon 4 carriers. However, there was no clear tendency for patients with CAA to have more severe or more numerous contusions (median contusion index 19 (CAA) v 14.5, p = 0.23, 95% CI for difference in medians -5 to 14). CONCLUSIONS: Presence of CAA in head injured cases was significantly associated with possession of an APOE epsilon 4 allele but not with the severity of contusions.

Trials and tribulations of using beta-amyloid precursor protein immunohistochemistry to evaluate traumatic brain injury in adults.

Axonal pathology is increasingly identified by beta-amyloid precursor protein (betaAPP) immunohistochemistry in the brains of patients who may or may not have a history of trauma. The presence of betaAPP-IR(+) has been variously interpreted as either that diffuse traumatic axonal injury (TAI) is indeed a universal finding in cases of fatal traumatic brain injury (TBI) or there are other causes of betaAPP-IR(+) axons which under certain circumstances may be sufficient to mimic TBI and therefore make the medico-legal interpretation of certain cases very difficult. To address some of the uncertainties we have undertaken a detailed analysis of the amount and distribution of betaAPP immunohistochemistry in 63 cases of fatal TBI, 17 cases of patients dying after cardiac arrest, 12 cases dying in association with status epilepticus, 3 cases of carbon monoxide (CO) poisoning, 13 cases of hypoglycaemia and in 60 controls. Three patterns of betaAPP-IR(+) were identified. First, diffuse multi-focal, second, corresponding to the outline of an infarct or haematoma, and thirdly a mixture of the two. The first pattern was seen in cases of the lesser grades of TAI, CO poisoning, and hypoglycaemia, the second pattern in cases in which there was evidence of raised intracranial pressure and the third in cases of severe TAI. It is concluded that the proper interpretation of cases requires the examination of a sufficient number of blocks ( [Formula: see text] ), processing using standardised protocols including betaAPP immunohistochemistry and in some cases the mapping of any IR(+) on anatomical line diagrams. betaAPP carried out on a small number of randomly taken blocks is likely to lead to misinterpretation of the clinico-pathological correlations and possibly to a miscarriage of justice.

Long-term intracerebral inflammatory response after traumatic brain injury.

Epidemiological and pathological studies suggest that head injury is a significant risk factor for subsequent neurodegeneration and cognitive decline in later life. The precise mechanisms for the development of post-traumatic neurodegenerative change are unclear but we hypothesize that persistence of inflammatory processes in the brain may play a key role and that some individuals are more susceptible to such changes based on their genetic make-up. In support of this hypothesis we present evidence of persistent elevated microglial activity in long-term survivors of head injury and the suggestion of an association between the extent of this activity and interleukin-1 genotype.

Axonal injury is accentuated in the caudal corpus callosum of head-injured patients.

Amyloid precursor protein (APP) accumulation is a sensitive marker for the axonal damage that is commonly seen in the brain as the result of head injury. This form of damage is particularly associated with midline structures such as the corpus callosum, although it is not clear whether some areas are more susceptible than others. The aim of this study was to determine if there was a differential distribution of axonal injury throughout the corpus callosum after head injury in an unselected group of cases. Coronal tissue sections from eight cases were taken at different levels through the corpus callosum, including the genu, body, and splenium. The sections were immunostained with an antibody to APP, and the amount of axonal damage at the different levels was quantified using computer image analysis to build up a rostro-caudal profile for each case. The profiles revealed a significantly higher APP load in caudal parts of the corpus callosum. This supports previous nonquantitative reports in the literature and has important implications in terms of choosing where tissue should be sampled to maximize the chance of detecting axonal injury post mortem.