Clayton A. Wiley

Selective neuronal vulnerability in HIV encephalitis.

Recent studies of human immunodeficiency virus type 1 (HIV-1) encephalitis have shown that in addition to well established white matter damage, the neocortex shows thinning, loss of large neurons and dendritic damage. In order to identify neuronal populations affected in HIV encephalitis and to determine how neuronal damage relates to the severity of HIV infection within the nervous system, we quantified parvalbumin (PV+) and neurofilament (NF+) immunoreactive neurons in the frontal cortex and hippocampus. We found that in the neocortex, the density of NF+ and PV+ neurons was independent of severity of HIV encephalitis, and therefore changes in these neuronal subsets did not account for previously reported neuronal loss. However, neuritic processes of PV+ neurons were fragmented, atrophic and in some cases distended. In contrast to the frontal cortex, there was a trend toward decreased density of PV+ neurons in the hippocampus which only reached significance in the CA3 layer where there was a 50–90% decrease in PV+ neurons. This decrease was closely correlated with the severity of HI V encephalitis. Double-label immunocytochemical analysis confirmed neuritic damage to intemeurons. These results suggest that HIV encephalitis differentially involves specific subpopulations of neurons. Since direct HIV infection of neuronal cells was not detected, damage to PV+ cells and fibers may be indirectly mediated by cytokines released by HIV-infected microglia.

HIV and HCMV coinfect brain cells in patients with AIDS

Direct interactions at the cellular level in vitro have been reported which suggest that opportunistic viruses may reactivate latent human immunodeficiency virus (HIV) in cells. The significance of these findings depends on whether coinfection of the same cell with these two different types of viruses occurs in vivo. Using various double-labeling techniques, we present evidence that human cytomegalovirus (HCMV) and HIV can coinfect the same cell in vivo in central nervous system tissue from AIDS patients. These observations indicate that direct cooperation at the single cell level could occur between HCMV and HIV. This new finding in the context of reports that herpesviruses can increase HIV transcription in vitro, suggest the possibility of a direct role for herpesviruses in the pathogenesis of AIDS.

Brain viral burden in HIV infection

We quantitated the brain viral burden in autopsy material from AIDS patients with and without HIV encephalitis. Central nervous system (CNS) samples from 45 AIDS autopsies with less than 48 hours postmortem autolysis and without significant non-viral opportunistic infections were analyzed using immunocytochemistry (ICC), antigen capture assay (ACA) and polymerase chain reaction (PCR). Approximately three-quarters of the cases contained HIV DNA by PCR. The majority of these had abundant gp41 detected by ICC, but approximately one-third had no HIV p24 detected by ACA. With all assays, HIV proteins and DNA were most abundant in deep gray matter. Approximately one-quarter of the cases contained HIV p24 by ACA in both CNS tissue and cerebrospinal fluid. In more than half of the cases cytomegalovirus was detectable in the brain by PCR, however, only in the basal ganglia of one case was human herpes virus-6 detectable by PCR. In conclusion, HIV infection of the CNS was observed in the majority of AIDS autopsies, however, the quantity of virus was variable between cases and within different neuroanatomical regions. Differences between the quantitation methods could be either technical or biological, however, any of them could be used to compare assessment of HIV burden by different laboratories.

Amyloid fibrils formed from a segment of the pancreatic islet amyloid protein

A synthetic peptide formed from residues 20-29 of the pancreatic islet amyloid protein has the confirmation of a twisted beta-pleated sheet protein suggesting it is a potential contributor toward amyloid fibril formation in the islets of Langerhans in Type 2 diabetes mellitus.

Localization of cytomegalovirus proteins and genome during fulminant central nervous system infection in an AIDS patient.

Approximately one-half of autopsied acquired immune deficiency syndrome (AIDS) patients demonstrate probable human cytomegalovirus (CMV) infection of the central nervous system (CNS). Because CMV in brain tissue or cerebrospinal fluid is difficult to culture, we used antisera, and radioactive probes to diagnose CMV infection in the brain of an autopsied AIDS patient, who died of a fulminant CNS and systemic infection with CMV, suggesting a complete seeding of the ependymal regions possibly followed by a uniform ventriculofugal spread of the virus deep into the parenchyma. Cytomegalic cells were observed in optic nerve, retina, ependymal and subependymal regions of the brain and in the motor (but not sensory) root-CNS junctions. Immunocytochemistry demonstrated viral antigen predominantly in cytomegalic cells, which also stained positively for glial fibrillary acidic protein, S-100, or neuron-specific enolase, but not a common leukocyte antigen. Virions were visible in these cells examined by electron microscopy. No viral replication was observed in pineocytes, pituicytes or the choroid plexus. Morphologically normal cells that were CMV antigen-negative proved to be infected after in situ hybridization with well-defined human CMV DNA fragments. Hence, morphologically normal glia and neurons show restricted replication of CMV, indicating that such cells may be latently infected.

Herpesviruses in chronic encephalitis associated with intractable childhood epilepsy

Herpesviruses (especially cytomegalovirus [CMV] and Epstein-Barr virus [EBV]) have been implicated in the pathogenesis of chronic (Rasmussen) encephalitis associated with epilepsy. To assess the presence of herpesvirus genes in brain tissue from epileptic children with chronic (usually Rasmussen type) encephalitis, DNA was extracted from surgically resected brain tissue and studied by the polymerase chain reaction using primers specific for CMV, varicella zoster virus, herpes simplex virus, EBV, and human herpesvirus 6 genes. By this technique evidence for the presence of low levels of CMV and EBV genes was detected in most brain specimens from encephalitis patients and in several brain specimens from patients without encephalitis (eg, cortical dysplasia, gliosis, or encephalomalacia) who also had intractable epilepsy. Occasionally, both EBV and CMV genes were found in the same brain. Signal strength for both CMV and EBV was much lower in epileptic brains than in the brains of acquired immunodeficiency syndrome patients with CMV encephalitis or brain lymphoma. We found evidence for infection of the brain by human herpesvirus 6 in only one patient with encephalitis. Polymerase chain reaction technology applied to resected brain tissue from epileptic patients may provide evidence for or against viral-mediated pathogenesis of Rasmussen encephalitis or other types of encephalitis. The small amounts of EBV and CMV genes found suggest that herpesvirus infection of the brain does not directly cause Rasmussen encephalitis.

Human immunodeficiency virus (HIV) and JC virus in acquired immune deficiency syndrome (AIDS) patients with progressive multifocal leukoencephalopathy

SummaryOf the 93 acquired immune deficiency syndrome (AIDS) patients autopsied between 1983 and 1986, 27 had evidence of viral encephalitis of which 3 had progressive multifocal leukoencephalopathy (PML), confirmed by electron microscopy. Using in situ hybridization with biotinylated JC virus probes, paraffin sections from the brains of these 27 patients were examined. JC virus was found only in those patients with histologically proven PML, while no evidence of JC virus was detected in the brains of the other 24 AIDS patients despite the presence of white matter pathology. Brain biopsies of the PML patients demonstrated human immunodeficiency virus (HIV)-infected macrophages infiltrating regions of demyelination. When the patients died (2 to 6 months after diagnosis of PML), many more macrophages contained HIV antigens and some had fused to form multinucleated giant cells. These findings suggest that in AIDS patients, papovaviruses not only cause damage by directly infecting oligodendroglia but causes additional damage by eliciting the ingress of macrophages latently infected with HIV. As was seen with other infections (e.g., cytomegalovirus) of the CNS this might be a general mechanism of HIV entry into the brain.

Cultured human brain capillary endothelial cells are permissive for infection by human cytomegalovirus.

Human cytomegalovirus (HCMV) infection is associated with a variety of systemic and neurologic diseases. In vitro HCMV growth is usually studied in fibroblasts, while in vivo HCMV growth is frequently observed in a wide variety of cell types including glia, neurons, and human brain capillary endothelial (HBCE) cells. To examine the biology of HCMV in HBCE cells, we have established a procedure for isolating these cells from human brain temporal lobectomies. Greater than 99.0% of these cultured cells were identified as HBCE cells on the basis of positive staining for factor VIII-related antigen-Von Willebrands factor (F VIII) and Ulex Europaeus agglutinin I (UEA I). HCMV antigens were detected by immunocytochemistry in HBCE cells after infection with strain AD 169. Intracellular virions were observed in infected cells by electron microscopy and infectious virus was released from HBCE cells. In addition, infected cells were confirmed as endothelial cells by double staining with antibodies to F VIII and HCMV.

Expression of Major Histocompatibility Complex Antigens in the Brains of Patients with Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is caused by JC virus (JCV) infection of the central nervous system (CNS) in immunosuppressed patients. The immunopathogenesis of this chronic encephalitis is unknown. Because major histocompatibility (MHC) class I and class II antigens are important in modulating the immune response and viral clearance, we examined the tissue expression of MHC molecules in relation to CNS damage and presence of virus. By immunocytochemical staining, both MHC class I and II antigens were expressed at high levels within PML lesions. Beta-2 microglobulin (β-2m) was present on endothelial cells and JCV-infected oligodendroglia within the lesions. Also, many astrocytes with bizarre morphology expressed MHC class I antigens. In histologically normal regions of PML brains expression of β-2m was noted only on endothelial cells. Expression of MHC class II also was focused within demyelinating lesions and was restricted to macrophages/microglia and occasional endothelial cells. When compared to other viral encephalitides (e.g. human immunodeficiency virus) these findings suggest that intra-CNS immune response to JCV is appropriate for antigenic presentation; however, the absence of responsive systemic T-cells may lead to chronic viral infection with progressive neuropathology.

Clinical and Histopathologic Study of Varicella Zoster Virus Retinitis in Patients With the Acquired Immunodeficiency Syndrome

Varicella zoster virus retinitis in patients with the acquired immunodeficiency syndrome is known to be a devastating disease. We studied a series of six consecutive patients that sheds new light on the clinical manifestations and treatment options of this disorder. All patients had episodes of cutaneous zoster, long-term exposure to oral acyclovir, and CD4+ T lymphocyte counts less than 50 cells/mm3. Two of the six patients had simultaneous radiographically demonstrable and histologically proven varicella zoster virus encephalitis; this is an important association. Histologic examination of autopsy specimens disclosed that the retinal infection by varicella zoster virus involves the retinal pigment epithelium more heavily than the inner retina, which is consistent with the characteristic clinical impression of an outer retinal necrosis.