BrainNet Europe's Code of Conduct for brain banking.

Research utilizing human tissue and its removal at post-mortem has given rise to many controversies in the media and posed many dilemmas in the fields of law and ethics. The law often lacks clear instructions and unambiguous guidelines. The absence of a harmonized international legislation with regard to post-mortem medical procedures and donation of tissue and organs contributes to the complexity of the issue. Therefore, within the BrainNet Europe (BNE) consortium, a consortium of 19 European brain banks, we drafted an ethical Code of Conduct for brain banking that covers basic legal rules and bioethical principles involved in brain banking. Sources include laws, regulations and guidelines (Declarations, Conventions, Recommendations, Guidelines and Directives) issued by international key organizations, such as the Council of Europe, European Commission, World Medical Association and World Health Organization. The Code of Conduct addresses fundamental topics as the rights of the persons donating their tissue, the obligations of the brain bank with regard to respect and observance of such rights, informed consent, confidentiality, protection of personal data, collections of human biological material and their management, and transparency and accountability within the organization of a brain bank. The Code of Conduct for brain banking is being adopted by the BNE network prior to being enshrined in official legislation for brain banking in Europe and beyond.

Brain viral burden, neuroinflammation and neurodegeneration in HAART-treated HIV positive injecting drug users.

The long-term impact of chronic human immunodeficiency virus (HIV) infection on brain status in injecting drug users (IDU) treated with highly active antiretroviral therapy (HAART) is unknown. Viral persistence in the brain with ongoing neuroinflammation may predispose to Alzheimer-like neurodegeneration. In this study, we investigated the brains of ten HAART-treated individuals (six IDU and four non-DU), compared with ten HIV negative controls (six IDU and four non-DU). HIV DNA levels in brain tissue were correlated with plasma and lymphoid tissue viral loads, cognitive status, microglial activation and Tau protein and amyloid deposition. Brain HIV proviral DNA levels were low in most cases but higher in HIV encephalitis (n = 2) and correlated significantly with levels in lymphoid tissue (p = 0.0075), but not with those in plasma. HIV positive subjects expressed more Tau protein and amyloid than HIV negative controls (highest in a 58 year old), as did IDU, but brain viral loads showed no relation to Tau and amyloid. Microglial activation linked significantly to HIV positivity (p = 0.001) and opiate abuse accentuated these microglial changes (p = 0.05). This study confirms that HIV DNA persists in brains despite HAART and that opiate abuse adds to the risk of brain damage in HIV positive subjects. Novel findings in this study show that (1) plasma levels are not a good surrogate indicator of brain status, (2) viral burden in brain and lymphoid tissues is related, and (3) while Tau and amyloid deposition is increased in HIV positive IDU, this is not specifically related to increased HIV burden within the brain.

Brain cell reservoirs of latent virus in presymptomatic HIV-infected individuals.

We detected HIV-1 DNA in pure populations of perivascular macrophages, parenchymal microglia, and astrocytes, isolated using laser microdissection from brain tissue of five untreated individuals who died in the presymptomatic stage of infection from non-HIV causes. HIV-1 DNA was detected in the three cell populations, most consistently in perivascular macrophages, without evidence of productive infection. The percentage of PCR reactions detecting HIV-1 DNA in perivascular macrophages correlated inversely with peripheral blood CD4 counts. These findings demonstrate that brain cell reservoirs of latent HIV-1 exist before pathological HIV encephalitis and suggest that perivascular macrophage trafficking of latent virus into the brain increases with immunosuppression.

Predisposition to accelerated Alzheimer-related changes in the brains of human immunodeficiency virus negative opiate abusers.

Cognitive impairment is a recognized effect of drug misuse, including the use of opiates. The pathological basis for this is unknown but the temporal and frontal cortices have been implicated. We have shown previously that deposits of hyperphosphorylated tau in drug user brains exceed those seen in age-matched controls. The present quantitative study of hyperphosphorylated tau and beta amyloid in drug user brains allows comparison with the related pathology in Alzheimer's disease. Brains were obtained from the Edinburgh Medical Research Council Brain Banks, comprising 39 human immunodeficiency virus negative drug users, five subjects with Alzheimer's disease and 37 age-matched, cognitively normal controls, all legally and ethically approved for research. Hyperphosphorylated tau positive (AT8, AT100) neuropil threads were significantly increased in the frontal and temporal cortex, and in the locus coeruleus, of drug users aged > 30 years (all P = 0.04). Under the age of 30 years, drug users showed a similar increase in neuropil threads compared with controls, but this reached significance only in the frontal cortex (P = 0.03). Immunopositivity for both three- and four-repeat tau was present in drug user brains. There was a direct relationship between the numbers of neuropil threads and of neurofibrillary tangles: neurofibrillary tangles were sparse in brains that had neuropil thread counts below 200 cm(2). Hyperphosphorylated tau positive neuropil threads increased at a faster rate in drug users than in controls and the levels of the phosphorylating enzyme, GSK-3, was raised in drug user brains. Beta amyloid (AB4, AB42 and 4G8) was raised in drug user brains (mainly as shadow plaques) but not significantly different from controls and there was no correlation between high beta amyloid and hyperphosphorylated tau in individual cases. Hyperphosphorylated tau levels correlated significantly (P = 0.038) with microglial activation in drug users but not in controls. The levels of hyperphosphorylated tau in drug users fell far short of those seen in Alzheimer's disease but overlapped with those in elderly controls. We conclude that drug users show early Alzheimer's disease-related brain pathology that may be the basis for cognitive impairment and that neuroinflammation is an early accompanying feature. This provides an opportunity to study the pathogenesis of tau pathology in the human brain.

Frequent infection of cerebellar granule cell neurons by polyomavirus JC in progressive multifocal leukoencephalopathy.

Progressive multifocal leukoencephalopathy (PML) occurs most often in immunosuppressed individuals. The lesions of PML result from astrocyte and oligodendrocyte infection by the polyomavirus JC (JCV); JCV has also been shown to infect and destroy cerebellar granule cell neurons (GCNs) in 2 human immunodeficiency virus (HIV)-positive patients. To determine the prevalence and pattern of JCV infection in GCNs, we immunostained formalin-fixed paraffin-embedded cerebellar samples from 40 HIV-positive and 3 HIV-negative PML patients for JCV, and glial and neuronal markers. The JCV infection was detected in 30 patients (70%); 28 (93%) of them had JCV-infected cells in the GC layer; JCV-infected GCNs were demonstrated in 15 (79%) of 19 tested cases. The JCV regulatory T antigen was expressed more frequently and abundantly in GCNs than JCV VP1 capsid protein. None of 37 HIV-negative controls but 1 (3%) of 35 HIV-positive subjects without PML had distinct foci of JCV-infected GCNs. Thus, JCV infection of GCNs is frequent in PML patients and may occur in the absence of cerebellar white matter demyelinating lesions. The predominance of Tantigen over VP1 expression in GCNs suggests that they may be the site of early or latent central nervous system JCV infection. These results indicate that infection of GCNs is an important, previously overlooked, aspect of JCV pathogenesis in immunosuppressed individuals.

Reactivation and mutation of newly discovered WU, KI, and Merkel cell carcinoma polyomaviruses in immunosuppressed individuals.

BACKGROUND: Infection with the human polyomaviruses BK (BKV) and JC (JCV) is almost ubiquitous, asymptomatic, and lifelong. However, reactivation during immunosuppression, associated with mutations in the transcriptional control region (TCR) that up-regulates viral replication, can cause life-threatening disease. In this study, we investigated whether the recently discovered WU and KI polyomaviruses (WUPyV and KIPyV) and Merkel cell polyomavirus (MCPyV) could, like BKV and JCV, persist, mutate, and reactivate in immunodeficient subjects. METHODS: Autopsy samples of lymphoid tissue from 42 AIDS-immunosuppressed subjects and 55 control samples were screened by polymerase chain reaction for all 5 polyomaviruses. TCR sequences from KIPyV and WUPyV recovered from both immunosuppressed and nonimmunosuppressed subjects were compared. RESULTS: Combined polyomavirus detection frequencies were much higher for the immunosuppressed group, compared with the nonimmunosuppressed group (35.7% vs. 3.6%), with viral loads in lymphoid tissues ranging from < or = 8.4 x 10(5) to > 1.5 x 10(5) viral genome copies per 10(6) cells. MCPyV was recovered from only 1 HIV-negative study subject. TCR sequences from reactivated WUPyV and KIPyV variants showed a number of point mutations and insertions that were absent in viruses recovered from respiratory tract specimens obtained from nonimmunosuppressed subjects. CONCLUSIONS: KIPyV and WUPyV show reactivation frequencies comparable to those of BKV and JCV during immunosuppression. TCR changes that potentially lead to transcriptional dysregulation may have pathogenic consequences equivalent in severity to those observed for JCV and BKV.

Postmortem tissue donation for research: a positive opportunity?

Previous research using human brain tissue has increased the understanding of many brain disorders, such as Alzheimer's disease and Creutzfeldt Jakob disease. However, there are other conditions, such as multiple sclerosis, which remain poorly understood and which require further investigation. The ongoing decline in the consented postmortem rate poses a threat to tissue collections and, consequently, future research. In the setting of the new Human Tissue legislation the authors set out to ascertain whether families recently and suddenly bereaved were willing to grant authorization for tissue samples and/or organs to be retained for research purposes at the time of medico-legal postmortem examination in adequate numbers to support the establishment of a brain and tissue bank. During the 2-year pilot phase of the project, 96% of families authorized retention of tissue samples for research and 17% agreed to whole brain donation. Respondents to a short questionnaire indicated that they were not further distressed by the approach and the majority were of the opinion that research donation should be offered to all bereaved families. This research concludes that the overwhelming majority of families who are recently and suddenly bereaved are willing to authorize research use of tissue taken at the time of postmortem examination.

Management of a twenty-first century brain bank: experience in the BrainNet Europe consortium.

Collections of human postmortem brains gathered in brain banks have underpinned many significant developments in the understanding of central nervous system (CNS) disorders and continue to support current research. Unfortunately, the worldwide decline in postmortem examinations has had an adverse effect on research tissue procurement, particularly from control cases (non-diseased brains). Recruitment to brain donor programmes partially addresses this problem and has been successful for dementing and neurodegenerative conditions. However, the collection of brains from control subjects, particularly from younger individuals, and from CNS disorders of sudden onset, remains a problem. Brain banks need to adopt additional strategies to circumvent such shortages. The establishment of brain bank networks allows data on, and access to, control cases and unusual CNS disorders to be shared, providing a larger resource for potential users. For the brain banks themselves, inclusion in a network fosters the sharing of protocols and development of best practice and quality control. One aspect of this collective experience concerns brain bank management, excellence in which is a prerequisite not only for gaining the trust of potential donors and of society in general, but also for ensuring equitable distribution to researchers of high quality tissue samples. This review addresses the legal, ethical and governance issues, tissue quality, and health and safety aspects of brain bank management and data management in a network, as well as the needs of users, brain bank staffing, donor programs, funding issues and public relations. Recent developments in research methodology present new opportunities for researchers who use brain tissue samples, but will require brain banks to adopt more complex protocols for tissue collection, preparation and storage, with inevitable cost implications for the future.

HIV-1-infected CD8+CD4+ T cells decay in vivo at a similar rate to infected CD4 T cells during HAART.

OBJECTIVES: To investigate the potential for CD4+CD8+ T cells [CD8 double positive (CD8 DP)] T cells to form a reservoir of HIV-1 following HAART through measurement of the rate of decay of infected CD4/CD8 DP T cells. METHODS: HIV-1 proviral loads in highly pure CD4 and CD8 DP T cells were determined for study subjects before and after 200-400 days of therapy and HIV-1 DNA decay rates were calculated. RESULTS: Before therapy, HIV-1 proviral load in CD8 DP correlated negatively with CD4 cell count. Decay rates of HIV-1-infected CD4 and CD8 DP T cells were similar. Rates for CD8 DP T cells correlated with the time to suppression of viral replication, whereas no such relationship was true for CD4 cell decay rates. A significant reduction in activated cells was observed for both cell types. The action of HAART on HIV-1 replication was similar for both CD4 cells and CD8 DP T cells, although the rate of clearance of infected CD8 DP T cells appeared more critical for a rapid reduction in plasma viral load. Although the size of the CD8 DP T cell reservoir in peripheral blood was smaller relative to that of CD4 cells, HAART did not completely clear HIV-1 infection from this cell subset. CONCLUSION: This study confirmed that CD8 DP T cells are a major reservoir for HIV-1 in vivo and, therefore, represent a potential reservoir for HIV-1 during HAART, in a manner analogous to that of CD4 T cells.

Virus immunocapture provides evidence of CD8 lymphocyte-derived HIV-1 in vivo.

OBJECTIVES: To demonstrate that HIV-1 immunocapture with an antibody against CD8 specifically captures virions derived from infected CD8 T cells, and to determine the proportion of HIV-1 derived from CD8 lymphocytes in plasma samples from HIV-infected individuals. METHODS: A virus capture method was developed to enable the detection of HIV-1 virions based upon the presence of certain cell-specific host-derived proteins (CD8, CD3, CD36) within the viral envelope. HIV-1 virions were captured using antibodies against these proteins and levels of bound virus were determined by quantitative reverse transcriptase-polymerase chain reaction. Highly pure CD8 and CD3+CD8- T-cell cultures were used as in-vitro models to determine the specificity of the virus capture technique. RESULTS: The in-vitro model demonstrates that incorporation of the CD8 molecule into released virions is specific to infection of CD8 T cells. Levels of HIV-1 immunocaptured from plasma of infected individuals using the anti-CD8 antibody indicate that up to 15% (range 10-33) of the plasma viral load is derived from CD8 lymphocytes. CONCLUSION: This study demonstrates for the first time that HIV-1-infected CD8 T cells can contribute substantially to levels of circulating virus during the course of infection. Levels of CD8-derived virus did not correlate with the level of infection of circulating CD8 T cells, but do show a significantly good fit to plasma viral loads based on a power model. The extensive infection of CD8 T cells implied by these results may contribute towards immune dysfunction and disease progression to AIDS.

Comparison of tissue distribution, persistence, and molecular epidemiology of parvovirus B19 and novel human parvoviruses PARV4 and human bocavirus.

BACKGROUND: PARV4 and human bocavirus (HBoV) are newly discovered human parvoviruses with poorly understood epidemiologies and disease associations. We investigated the frequencies of persistence, tissue distribution, and influence of immunosuppression on replication of these viruses. METHODS: At autopsy, bone marrow, lymphoid tissue, and brain tissue from human immunodeficiency virus (HIV)-infected individuals with acquired immunodeficiency syndrome (AIDS) and those without AIDS and from HIV-uninfected individuals were screened for parvovirus B19, PARV4, and HBoV DNA by means of quantitative polymerase chain reaction analyses. RESULTS: B19 DNA was detected both in HIV-infected study subjects (13 of 24) and in HIV-uninfected study subjects (8 of 8), whereas PARV4 DNA was detected only in HIV-infected study subjects (17 of 24). HBoV DNA was not detected in any study subjects. The degree of immunosuppression with HIV infection did not influence B19 or PARV4 viral loads. B19 or PARV4 plasma viremia was not detected in any study subjects (n=76; viral load <25 DNA copies/mL). A significantly older age distribution was found for study subjects infected with B19 genotype 2, compared with those infected with B19 genotype 1. Two genotypes of PARV4 were detected; study subjects carrying prototype PARV4 (genotype 1) were younger (all born after 1958) than those infected with genotype 2 (PARV5; study subjects born between 1949 and 1956). CONCLUSIONS: Tight immune control of replication of B19 and PARV4 was retained despite profound immunosuppression. Recent genotype replacement of PARV4, combined with absent sequence diversity among genotype 1 sequences, suggests a recent, epidemic spread in the United Kingdom, potentially through transmission routes shared by HIV.

Parenteral transmission of the novel human parvovirus PARV4.

Transmission routes of PARV4, a newly discovered human parvovirus, were investigated by determining frequencies of persistent infections using autopsy samples from different risk groups. Predominantly parenteral routes of transmission were demonstrated by infection restricted to injection drug users and persons with hemophilia and absence of infection in homosexual men with AIDS and low-risk controls.

Macrophage entry mediated by HIV Envs from brain and lymphoid tissues is determined by the capacity to use low CD4 levels and overall efficiency of fusion.

HIV infects macrophages and microglia in the central nervous system (CNS), which express lower levels of CD4 than CD4+ T cells in peripheral blood. To investigate mechanisms of HIV neurotropism, full-length env genes were cloned from autopsy brain and lymphoid tissues from 4 AIDS patients with HIV-associated dementia (HAD). Characterization of 55 functional Env clones demonstrated that Envs with reduced dependence on CD4 for fusion and viral entry are more frequent in brain compared to lymphoid tissue. Envs that mediated efficient entry into macrophages were frequent in brain but were also present in lymphoid tissue. For most Envs, entry into macrophages correlated with overall fusion activity at all levels of CD4 and CCR5. gp160 nucleotide sequences were compartmentalized in brain versus lymphoid tissue within each patient. Proline at position 308 in the V3 loop of gp120 was associated with brain compartmentalization in 3 patients, but mutagenesis studies suggested that P308 alone does not contribute to reduced CD4 dependence or macrophage-tropism. These results suggest that HIV adaptation to replicate in the CNS selects for Envs with reduced CD4 dependence and increased fusion activity. Macrophage-tropic Envs are frequent in brain but are also present in lymphoid tissues of AIDS patients with HAD, and entry into macrophages in the CNS and other tissues is dependent on the ability to use low receptor levels and overall efficiency of fusion.

Impact of HIV on regional & cellular organisation of the brain.

There are many excellent reviews of HIV infection of the nervous system. However these all assume that the reader has a working knowledge of the structure and cellular architecture of the brain. It may be that specialised brain vocabulary represents an unwelcome hurdle for those scientists with expert knowledge of the effects of HIV in other cell systems and who wish to extend that interest to the brain. This review provides an introduction to the component structures and cells of the brain and an overview of their involvement in HIV/AIDS. HIV infection leads to death through its capacity to progressively devastate the immune system. Current anti-HIV therapy has achieved considerable success in halting and partially reversing this process. In the absence of treatment, the breakdown of immunity is marked by declining CD4 counts and increasing vulnerability to opportunistic infections. In parallel with these effects on the lymphoid system, the nervous system is frequently the site of an initially stealthy infection which leads ultimately to symptomatic disease in a significant proportion of HIV infected individuals. The most feared manifestation of central nervous system (CNS) involvement is dementia. Unfortunately, serial CD4 counts and measurement of blood viral load do not serve to identify or monitor early infection of brain tissue. Since effective anti-HIV therapy has not achieved eradication of virus from lymphoid tissues, and anti-HIV drugs do not enter the nervous system easily, it is hardly surprising that HIV infection of the nervous system continues to cause clinical problems. Even in treatment-compliant patients, a measurable degree of cognitive impairment may develop, signalling previous or present HIV-related brain injury. The cause of HIV associated dementia and cognitive disability remains poorly understood. Perhaps most significantly, the long-term consequences of clinically occult brain infection are unknown and will require further investigation.

Accelerated Tau deposition in the brains of individuals infected with human immunodeficiency virus-1 before and after the advent of highly active anti-retroviral therapy.

This study aims to investigate the influence of human immunodeficiency virus (HIV) infection on the neurodegenerative processes normally associated with ageing. We have looked for evidence of beta amyloid and hyperphosphorylated Tau deposition in HIV-infected subjects before and after the advent of highly active anti-retroviral therapy (HAART). In addition we have looked for evidence of axonal damage. We have compared these HIV-positive cases with age-matched controls and with older non-demented controls. We find no evidence of significant premature beta amyloid deposition in HIV-infected cases; however, we do observe elevated levels of hyperphosphorylated Tau in the hippocampus of many HIV-infected subjects, compared with age-matched controls. The greatest levels of hyperphosphorylated Tau are noted in HAART-treated subjects. Axonal damage marked by expression of beta amyloid pre-cursor protein (BAPP) was highly variable in all groups including control subjects. We surmise that HIV infection and/or the use of anti-retroviral therapy may predispose to accelerated neuroageing in the form of hyperphosphorylated Tau deposition in the hippocampus. Within the age groups studied these significant neuropathological changes remained subclinical and were not yet associated with cognitive impairment.

Neurobiology of multiple insults: HIV-1-associated brain disorders in those who use illicit drugs.

Despite two decades of research, certain aspects of HIV-related central nervous system (CNS) disease remain poorly understood. HIV targets microglia and macrophages within the CNS and enters the brain compartment early. However, HIV is there held in check apparently until the onset of significant immune compromise, when viral replication, microglial activation, neuronal damage, and cognitive impairment are likely to ensue. Illicit drug abuse continues to be a significant risk factor for HIV transmission worldwide. Whether HIV-related CNS disease is more prevalent or more severe in this risk group has long been debated. Drugs of abuse can of themselves cause immune suppression, blood-brain barrier breakdown, microglial activation, and neuronal injury. This review presents evidence that HIV associated CNS disorders are indeed accentuated in drug abusers. However, the advent of effective therapy has added a new dimension, which must be taken into consideration. Treated individuals are surviving much longer and HIV encephalitis and HIV-associated dementia have become much less common. However, more subtle forms of CNS damage are emerging. Examination of the brains of individuals who have been treated long term with highly active antiretroviral therapy (HAART) reveals a surprising degree of microglial activation, comparable at times to that seen formerly in milder cases of HIV encephalitis. In addition, these individuals show evidence of increased deposition of neurodegenerative proteins, particularly hyperphosphorylated tau. Similar observations have been made in young opiate abusers who are HIV negative. Taken together, these results suggest that neuroinflammation and neurodegeneration, which are clinically silent at present, may cause problems in the future in HAART-treated subjects.

Cells of the central nervous system as targets and reservoirs of the human immunodeficiency virus.

The availability of highly active antiretroviral therapies (HAART) has not eliminated HIV-1 infection of the central nervous system (CNS) or the occurrence of HIV-associated neurological problems. Thus, the neurobiology of HIV-1 is still an important issue. Here, we review key features of HIV-1-cell interactions in the CNS and their contributions to persistence and pathogenicity of HIV-1 in the CNS. HIV-1 invades the brain very soon after systemic infection. Various mechanisms have been proposed for HIV-1 entry into the CNS. The most favored hypothesis is the migration of infected cells across the blood-brain barrier ("Trojan horse" hypothesis). Virus production in the CNS is not apparent before the onset of AIDS, indicating that HIV-1 replication in the CNS is successfully controlled in pre-AIDS. Brain macrophages and microglia cells are the chief producers of HIV-1 in brains of individuals with AIDS. HIV-1 enters these cells by the CD4 receptor and mainly the CCR5 coreceptor. Various in vivo and cell culture studies indicate that cells of neuroectodermal origin, particularly astrocytes, may also be infected by HIV-1. These cells restrict virus production and serve as reservoirs for HIV-1. A limited number of studies suggest restricted infection of oligodendrocytes and neurons, although infection of these cells is still controversial. Entry of HIV-1 into neuroectodermal cells is independent of the CD4 receptor, and a number of different cell-surface molecules have been implicated as alternate receptors of HIV-1. HIV-1-associated injury of the CNS is believed to be caused by numerous soluble factors released by glial cells as a consequence of HIV-1 infection. These include both viral and cellular factors. Some of these factors can directly induce neuronal injury and death by interacting with receptors on neuronal membranes (neurotoxic factors). Others can activate uninfected cells to produce inflammatory and neurotoxic factors and/or promote infiltration of monocytes and T-lymphocytes, thus amplifying the deleterious effects of HIV-1 infection. CNS responses to HIV-1 infection also include mechanisms that enhance neuronal survival and strengthen crucial neuronal support functions. Future challenges will be to develop strategies to prevent HIV-1 spread in the brain, bolster intrinsic defense mechanisms of the brain and to elucidate the impact of long-term persistence of HIV-1 on CNS functions in individuals without AIDS.

Preclinical vCJD after blood transfusion in a PRNP codon 129 heterozygous patient.

We report a case of preclinical variant Creutzfeldt-Jakob disease (vCJD) in a patient who died from a non-neurological disorder 5 years after receiving a blood transfusion from a donor who subsequently developed vCJD. Protease-resistant prion protein (PrP(res)) was detected by western blot, paraffin-embedded tissue blot, and immunohistochemistry in the spleen, but not in the brain. Immunohistochemistry for prion protein was also positive in a cervical lymph node. The patient was a heterozygote at codon 129 of PRNP, suggesting that susceptibility to vCJD infection is not confined to the methionine homozygous PRNP genotype. These findings have major implications for future estimates and surveillance of vCJD in the UK.

Effects of human immunodeficiency virus encephalitis and drug abuse on the B lymphocyte population of the brain.

We aimed to assess the effects of human immunodeficiency virus (HIV) encephalitis (HIVE) on the B-lymphocyte population of the brain. We also tested the effects of intravenous opiate drug abuse because this is a major risk factor for infection, with known immunosuppressive properties. Immunohistochemistry was used to identify B lymphocytes in the brains of clinically well-characterized HIV-negative drug abusers, individuals with HIVE, and, for comparison, HIV-negative individuals with encephalitis. Perivascular and parenchymal B lymphocytes were studied in 11 regions of each brain. We found that despite a small apparent rise, the abuse of opiate drugs had no significant effect on the B-lymphocyte population of the brain. Individuals with HIVE were found to have a greater number of B lymphocytes in brain tissue than individuals with acquired immunodeficiency syndrome (AIDS) who had no central nervous system (CNS) pathology. However, in comparison to nonimmunocompromised individuals with encephalitis, the B-lymphocyte population of HIVE brains was greatly reduced. We suggest that this latter finding may be linked to declining CD4 T-lymphocyte levels in end-stage AIDS, and that CD4 T lymphocytes may be required for efficient entry of B lymphocytes to the CNS. The brain B-lymphocyte population correlated well with CD4 T-lymphocyte level in the blood, in cases with viral encephalitis. These findings suggest that systemic immune competence is required to mount a full B-lymphocyte response to viral CNS infections. Furthermore, we suggest that CD4 T lymphocytes may play a key role in the humoral immune response to viral infection of the brain.

Prion protein accumulation and neuroprotection in hypoxic brain damage.

The function of the normal conformational isoform of prion protein, PrP(C), remains unclear although lines of research have suggested a role in the cellular response to oxidative stress. Here we investigate the expression of PrP(C) in hypoxic brain tissues to examine whether PrP(C) is in part regulated by neuronal stress. Cases of adult cerebral ischemia and perinatal hypoxic-ischemic injury in humans were compared with control tissues. PrP(C) immunoreactivity accumulates within neuronal processes in the penumbra of hypoxic damage in adult brain, and within neuronal soma in cases of perinatal hypoxic-ischemic injury, and in situ hybridization analysis suggests an up-regulation of PrP mRNA during hypoxia. Rodents also showed an accumulation of PrP(C) in neuronal soma within the penumbra of ischemic lesions. Furthermore, the infarct size in PrP-null mice was significantly greater than in the wild type, supporting the proposed role for PrP(C) in the neuroprotective adaptive cellular response to hypoxic injury.