HIV mediates a productive infection of the brain

BACKGROUND

Approximately one quarter of patients with AIDS develop severe cognitive deficits called HIV-associated dementia complex. There is some controversy regarding the importance of viral load and distribution in mediating this neurologic disease.

OBJECTIVE

Brain HIV proviral and RNA loads were compared to define the molecular nature of HIV infection of the brain.

METHOD

Neuropathologic examination was performed on brains from 10 autopsies of patients with AIDS that had short post-mortem intervals and no evidence of opportunistic infection. Viral DNA and RNA were extracted and quantified from multiple brain regions. These findings were compared with triple-label immunofluorescence for viral and cell markers.

RESULTS

Brains with histopathologic evidence of HIV encephalitis contained abundant HIV RNA and DNA. Regions without productive HIV infection showed minimal proviral load. By immunocytochemistry, only brain macrophages/microglia double labeled for viral proteins.

CONCLUSIONS

HIV mediates a productive infection of brain macrophages/microglia. There was no evidence supporting the hypothesis of substantial neuronal or macroglial infection, or evidence of substantial proviral burden prior to the development of productive infection.

Absence of brain-derived neurotrophic factor and trkB receptor immunoreactivity in glia of Alzheimer's disease

Alterations in the neuronal expression of some neurotrophins have been shown in various neurodegenerative processes, particularly Alzheimer's disease (AD). Glia may up-regulate neurotrophins and their high-affinity tyrosine kinase (trk) receptors in response to neural injury. In human immunodeficiency virus type 1 (HIV-1) encephalitis, activated microglia were shown to express brain-derived neurotrophic factor (BDNF), while reactive astrocytes expressed trkB receptor. This observation has suggested the existence of local neurotrophic regulation between different glial populations. To characterize the glial cellular distribution of BDNF and trkB receptor proteins in AD, we studied selected regions of postmortem brains from four AD and three age-matched control patients by double-immunofluorescence confocal microscopy. In both groups, BDNF immunoreactivity was distributed in neuronal perikarya and neuritic processes in the neocortex and hippocampus. No BDNF immunoreactivity was observed in microglia or astrocytes within and between senile plaques of AD. Catalytic trkB receptor immunoreactivity was present in neuronal perikarya in the neocortex and hippocampus. Reactive astrocytes and microglia were not immunoreactive for catalytic trkB. The absence of BDNF and trkB proteins in glia in AD patients is in contrast to the finding in patients with HIV-1 encephalitis. This difference suggests that glial expression of BDNF and trkB proteins may be characteristic of particular disease processes, rather than merely representing a stereotyped response to any type of neural injury.

Tyramide signal amplification method in multiple-label immunofluorescence confocal microscopy

The tyramide signal amplification (TSA) method has recently been introduced to improve the detection sensitivity of immunohistochemistry. We present three examples of applying this method to immunofluorescence confocal laser microscopy: (1) single labeling for CD54 in frozen mouse brain tissue; (2) double labeling with two unconjugated primary antibodies raised in the same host species (human immunodeficiency virus type 1 p24 and CD68) in paraffin-biopsied human lymphoid tissue; and (3) triple labeling for brain-derived neurotrophic factor, glial fibrillary acidic protein, and HLA-DR in paraffin-autopsied human brain tissue. The TSA method, when properly optimized to individual tissues and primary antibodies, is an important tool for immunofluorescence microscopy. Furthermore, the TSA method and enzyme pretreatment can be complementary to achieve a high detection sensitivity, particularly in formalin-fixed paraffin-embedded archival tissues. Using multiple-label immunofluorescence confocal microscopy to characterize the cellular localization of antigens, the TSA method can be critical for double labeling with unconjugated primary antibodies raised in the same host species.

Intravitreal toxicology and therapeutic efficacy of the carboxymethyl ester of the 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA-O-Me), a novel lipid antiviral prodrug for intraocular drug delivery

This study was conducted to evaluate the vitreous clarity and intraocular therapeutic index of three preparations ofthe carboxymethyl ester of 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA-O-Me), a long acting lipid derivative of foscarnet with potent anti-CMV activity. Twenty-six New Zealand white rabbits were intravitreally injected with one of three preparations of ODG-PFA-O-Me or control diluent. The vitreous clarity was graded after injection using indirect ophthalmoscopy and fundus photography. Drug intraocular toxicity was evaluated by electroretinography and by post-sacrifice tissue pathology using light and electron microscopy. Intravitreal injection of micellar ODG-PFA-O-Me showed variable local retinal toxicity and vitreal compound aggregates in eyes with the middle and high doses. The intraocular therapeutic index was lower than 465:1. Intravitreal injection of liposomal ODG-PFA-O-Me, either free acid or sodium salt, revealed clear vitreous for the 0.632 and 0.84 mM final intravitreal concentrations. No retinal toxicity was confirmed for the 1.12 mM final intravitreal concentration at the eight week observation following injection. The intraocular therapeutic index was between 585-1037:1. ODG-PFA-O-Me possesses better vitreous compatibility than ODG-PFA. Liposomal ODG-PFA-O-Me can be intravitreally injected with a resulting clear vitreous and high intraocular therapeutic index. Liposomal ODG-PFA-O-Me could be a long acting nontoxic intravitreous injectable drug for CMV retinitis.

Intravitreal toxicology in rabbits of two preparations of 1-O-octadecyl-sn-glycerol-3-phosphonoformate, a sustained-delivery anti-CMV drug

PURPOSE

To determine intraocular toxicity and efficacy of the lipid prodrug of foscarnet, 1-O-octadecyl-sn-glycerol-3-phosphonoformate (ODG-PFA), as a long-acting, nontoxic intravitreous injectable drug delivery system for cytomegalovirus (CMV) retinitis.

METHODS

ODG-PFA was synthesized by coupling the phosphonate residue of PFA to the 3 hydroxyl of 1-O-octadecyl-sn-glycerol and formulated as micelles and liposomes at concentrations so that, after injection into the rabbit vitreous, the resultant intravitreal concentrations were 0.2 mM, 0.63 mM, and 2 mM in micellar formulation and 0.02 mM, 0.063 mM, 0.2 mM, and 0.63 mM for liposomal formulation. The compounds were injected, and toxicology evaluations were performed.

RESULTS

Intravitreal injections of micellar ODG-PFA resulted in aggregation of the material in vitreous and variable local retinal damage. Intravitreal injections of the liposomal ODG-PFA revealed even dispersion of the compounds and a clear vitreous, using final concentration in the vitreous of 0.2 mM. No intraocular toxicity was found with the 0.632 mM final concentration. The 50% inhibitory concentration (IC50) for CMV of ODG-PFA was 0.43+/-0.27 microM, and the therapeutic index of ODG-PFA after intravitreal injection was estimated to be 1470:1.

CONCLUSIONS

Lipid-derivatized foscarnet liposome formulations may be a useful long-acting delivery system for the therapy of CMV retinitis.

Acquired immunodeficiency syndrome-related intraocular B-cell lymphoma

OBJECTIVES

To present the full clinical spectrum of the acquired immunodeficiency syndrome-related intraocular lymphoma as manifested in the eye, specifically retinal lymphoma associated with primary central nervous system lymphoma, isolated ocular lymphoma, and choroidal lymphoma associated with systemic lymphoma.

METHODS

Three patients with acquired immunodeficiency syndrome were noted to have atypical retinal lesions. Diagnostic retinal biopsy in 2 patients and postmortem examination of the eyes in the third case were performed.

RESULTS

Diagnostic retinal biopsy in the first 2 patients revealed retinal B-cell lymphoma. Initial systemic evaluation showed the eyes to be the sole site of disease. Later, in 1 of these patients, the lymphoma spread to the brain. The third patient developed an acute abdomen 4 months after the development of his ocular findings. The histological evaluation of the resected bowel revealed high-grade B-cell lymphoma. The patient died 1 week later and postmortem analysis of the eyes disclosed the presence of lymphoma in the choroid of both eyes.

CONCLUSIONS

This is the most complete series of patients with acquired immunodeficiency syndrome-related intraocular B-cell lymphoma and, to our knowledge, provides the first 2 cases diagnosed by retinal biopsy. These 3 cases present the full clinical spectrum of the disease as manifested in the eye.

Neuron-enriched second trimester human cultures: growth factor response and in vivo graft survival

Grafts of first trimester fetal tissue show limited survival and integration in the adult CNS. Alternative grafting strategies have been sought for treatment of neurodegenerative disease. We have developed cultures of human second trimester fetal tissues to study neuronal differentiation. Grafted into the SCID mouse striatum, aggregates of these cultures formed neuron-rich xenografts for at least 8 months. We examined the influence of various neurotrophic factors, including basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), transforming growth factor-beta 1 (TGF-beta1), and hepatocyte growth factor (HGF), on the growth and differentiation of neuronal and glial cell populations. BDNF promoted the survival and differentiation of second trimester neurons whereas bFGF exhibited a strong proliferative effect on precursors and the astroglial population. Our data suggest that second trimester human fetal cultures contain neuroprogenitor cells that can be directed to the neuronal lineage. This process may be amplified by treatment with BDNF, which we hypothesize could improve the long-term in vivo survival of neuron-enriched grafts.

Expression of brain-derived neurotrophic factor protein in activated microglia of human immunodeficiency virus type 1 encephalitis

The role of neurotrophic factors and their therapeutic potential have been investigated in various neurodegenerative disorders. In neurodegeneration associated with human immunodeficiency virus (HIV) infection, neuronal function and survival may be affected by abnormal neurotrophic regulation involving HIV-infected microglia and reactive astrocytes. To characterize the cellular localization of brain-derived neurotrophic factor (BDNF) and its high-affinity tyrosine kinase receptor, trkB, proteins in HIV-1 encephalitis, we examined post-mortem brains from patients with acquired immunodeficiency syndrome and brains from non-HIV-infected controls. Using double immunofluorescent confocal microscopy, we found that BDNF immunoreactivity was distributed in neocortical neuronal perikarya and neuritic processes, while in the striatum only neurites were BDNF-immunoreactive. Additionally, the striatum with HIV infection was characterized by BDNF immunoreactivity in infiltrating activated microglia/macrophages and multinucleated giant cells. Catalytic trkB receptor immunoreactivity was observed in neuronal perikarya in the neocortex and striatum, as well as in reactive astrocytes within HIV-infected regions. Our findings suggest that expression of BDNF by activated microglia in HIV-1 encephalitis may affect neuronal survival and astroglial response through corresponding trkB receptors.

High-dose (2000-microgram) intravitreous ganciclovir in the treatment of cytomegalovirus retinitis

OBJECTIVE

The authors prospectively studied visual outcome, relapse, complications, and survival of patients with acquired immune deficiency syndrome (AIDS)-related cytomegalovirus (CMV) treated with high-dose intravitreous ganciclovir (2 mg/0.1 ml) injections. The outcomes were compared with those of patients treated with standard doses of intravenous ganciclovir in the same institution. The histopathologic and electrophysiologic effects of high-dose intravitreous ganciclovir injections in rabbits also were studied.

DESIGN

A nonrandomized case series.

PARTICIPANTS

A total of 42 patients (74 eyes) were treated with intravitreous injections and 18 patients (27 eyes) were treated with intravenous ganciclovir. Five eyes of three New Zealand white rabbits were injected with ganciclovir, and the sixth eye was a control specimen.

INTERVENTION

Patients treated with intravitreous injections received twice-weekly doses of 2 mg/0.1 ml ganciclovir for 3 weeks, then weekly injections. Patients treated with intravenous ganciclovir received standard doses. Patients were monitored with regular examinations. Rabbit eyes were given intravitreous injections of 1 mg/0.1 ml of ganciclovir weekly for 4 weeks.

MAIN OUTCOME MEASURES

Assessments of vision, retinal inflammation, and survival were made. Electroretinograms were performed on the rabbit eyes, and they were processed for light and electron microscopy.

RESULTS

In the intravitreous group, visual acuity (VA) was stable in 64 of 74 eyes, 5 improved, and 5 deteriorated. Sixty-three (85%) of 74 eyes had final VA of 20/20 to 20/40. Relapse occurred in five eyes (7%; median time, 42 weeks). There were three cases of endophthalmitis. Median survival after diagnosis of CMV retinitis was 36 weeks. In the intravenous group, VA was stable in 18 eyes, 0 improved, and 9 deteriorated. Sixteen (59%) of 27 eyes had final VA of 20/20 to 20/40. Relapse occurred in 15 eyes (56%) at a median time of 21 weeks. Median survival was 21 weeks. The rabbit studies showed no evidence of toxicity.

CONCLUSION

High-dose intravitreous ganciclovir effectively suppressed CMV retinitis, preserved vision, and prevented relapse without deterioration in survival.

Sources of the neurotoxin quinolinic acid in the brain of HIV-1-infected patients and retrovirus-infected macaques

This study investigated the sources of quinolinic acid, a neurotoxic tryptophan-kynurenine pathway metabolite, in the brain and blood of HIV-infected patients and retrovirus-infected macaques. In brain, quinolinic acid concentrations in HIV-infected patients were elevated by > 300-fold to concentrations that exceeded cerebrospinal fluid (CSF) by 8.9-fold. There were no significant correlations between elevated serum quinolinic acid levels with those in CSF and brain parenchyma. Because nonretrovirus-induced encephalitis confounds the interpretation of human postmortem data, rhesus macaques infected with retrovirus were used to examine the mechanisms of increased quinolinic acid accumulations and determine the relationships of quinolinic acid to encephalitits and systemic responses. The largest kynurenine pathway responses in brain were associated with encephalitis and were independent of systemic responses. CSF quinolinic acid levels were also elevated in all infected macaques, but particularly those with retrovirus-induced encephalitis. In contrast to the brain changes, there was no difference in any systemic measure between macaques with encephalitis vs. those without. Direct measures of the amount of quinolinic acid in brain derived from blood in a macaque with encephalitis showed that almost all quinolinic acid (>98%) was synthesized locally within the brain. These results demonstrate a role for induction of indoleamine-2,3dioxygenase in accelerating the local formation of quinolinic acid within the brain tissue, particularly in areas of encephalitis, rather than entry of quinolinic acid into the brain from the meninges or blood. Strategies to reduce QUIN production, targeted at intracerebral sites, are potential approaches to therapy.

Chemokines and receptors in HIV encephalitis

BACKGROUND

Chemokines are involved in the migration of leukocytes and have been implicated in several inflammatory diseases of the central nervous system. Some of their receptors have been proposed to mediate HIV infection.

OBJECTIVE

To determine changes in chemokine and receptor expression in HIV encephalitis, and to determine whether upregulation leads to recruitment of infected monocytes across the blood-brain barrier and participates in HIV neuropathology.

METHODS

Immunocytochemistry and double-label immunofluorescent laser confocal microscopy was performed with antibodies to chemokines and their receptors on brain tissues from patients who died with or without HIV encephalitis. In vivo distribution was compared with in vitro cultures of human neuroglial cells.

RESULTS

The beta-chemokines monocyte chemotactic protein-1, macrophage inflammatory protein-1alpha, and RANTES were detected on brain macrophages. Their presence was associated with the histopathological signs of HIV encephalitis. The alpha-chemokines IP-10 (10 kDa inflammatory protein) and interleukin-8 were expressed by astrocytes in all tissues, including controls. Presence of the CXC-chemokine receptor (CXCR)-4 was seen on brain macrophages/microglia, neurons, and astrocytes. CC-Chemokine receptor (CCR)-5 was detected only on macrophages/microglia. CCR-3 and CCR-1 were expressed by macrophages and endothelial cells. In vitro studies examining the presence of CCR-3, CCR-5, and CXCR-4 on human brain cell cultures demonstrated abundant neuronal and microglial expression.

CONCLUSIONS

Expression of a variety of chemokines and receptors was shown to be increased in HIV encephalitis brain tissues particularly in areas of neuroglial reaction. The expression pattern supported their involvement in the recruitment of inflammatory infiltrates and formation of microglial nodules. Presence of chemokine receptors on neurons may be involved in the pathogenesis of neurologic damage in AIDS patients.

Confocal microscopy assessment of lymphoid tissues with follicular hyperplasia from patients infected with human immunodeficiency virus type 1

OBJECTIVE

To characterize human immunodeficiency virus (HIV) infection of lymphoid tissues during follicular hyperplasia.

METHODS

We examined 10 tonsil/adenoid, 3 parotid lymphoepithelial cyst, and 7 lymph node specimens that had been surgically removed from 13 patients infected with HIV-1. Characteristics of productive HIV-1 infection were assessed using immunocytochemistry for HIV-1 p24. Cellular colocalization was determined with the aid of a confocal microscope using double immunofluorescent staining for HIV-1 p24 and cell-specific markers.

RESULTS

All specimens showed follicular hyperplasia. Using confocal microscopy with three-dimensional reconstruction, HIV-1 p24 was seen to be "intimately" colocalized with CD21 within the germinal centers. While lymphoid follicles were generally hyperplastic, only a subset of these follicles contained HIV-1 p24. Occasional HIV-1-expressing mononuclear cells identified outside follicles stained for CD68 or CD3.

CONCLUSIONS

The differential involvement of hyperplastic follicles by HIV-1 within individual lymphoid tissues and the intimate colocalization of HIV-1 p24 and CD21 suggest that infected follicular dendritic cells may be an important reservoir of HIV-1 during follicular hyperplasia.

Brain HIV burden and length of survival after AIDS diagnosis

Patients with AIDS in the late stages of disease can develop dementia. Previous studies have suggested HIV encephalitis is the pathological substrate of HIV-associated dementia. We hypothesized that patients who survive longer after the initial diagnosis of AIDS would have a higher brain HIV burden and consequently manifest dementia. We examined the relationship between length of survival after AIDS diagnosis and the presence of HIV encephalitis or HIV-associated dementia. We studied retrospectively the following parameters in 74 consecutive AIDS autopsies: length of survival after AIDS diagnosis, clinical diagnosis of dementia, and neuropathologic findings (including HIV burden assessment). Multinucleated giant cells (MNGC) were identified in 20% of the brains studied. HIV gp41 was detected by immunocytochemistry in 54%, approximately half of which had abundant HIV burden. Brains from all 4 patients who were clinically diagnosed with dementia and had no opportunistic neuropathologic changes contained MNGC and abundant HIV burden. Survival after AIDS diagnosis was significantly longer in patients with MNGC (p = 0.03) or abundant HIV burden (p = 0.02). A trend toward longer survival after AIDS diagnosis was apparent in patients with dementia, but did not reach statistical significance. These findings suggest that prolonged survival with immunosuppression may be a prerequisite for the development of HIV encephalitis.

Dendritic injury is a pathological substrate for human immunodeficiency virus-related cognitive disorders. HNRC Group. The HIV Neurobehavioral Research Center

To determine the neuropathological substrate of human immunodeficiency virus (HIV)-associated neurocognitive disorders, we examined persons with acquired immunodeficiency syndrome before their death and related their antemortem neuropsychological performance to postmortem indicators of HIV encephalitis, viral burden, and presynaptic and postsynaptic neuronal injury. Of 20 prospectively examined cases, 9 were neurocognitively normal, 5 showed neuropsychological impairment, 5 had minor cognitive/motor disorder, and 1 was demented. Degree of neurocognitive impairment was strongly related to the amount of dendritic simplification based on microtubule-associated protein 2 immunohistochemical staining, somewhat less so to a semiquantitative viral burden score based on numbers of HIV gp41-immunoreactive cells, and much less so to the presence of multinucleated giant cells or microglial nodules. It appears that even milder neurocognitive impairment reflects microneuroanatomical injury to synaptic structures.

Adverse events and autopsy findings after intravitreous cidofovir (HPMPC) therapy in patients with acquired immune deficiency syndrome (AIDS)

OBJECTIVE

The purpose of the study is to evaluate the adverse events and autopsy findings in a series of consecutive 20-microg intravitreous cidofovir injections at a single institution.

DESIGN

The study design was a nonrandomized, consecutive case series.

PARTICIPANTS

Seventy-six patients with acquired immune deficiency syndrome with cytomegalovirus retinitis were studied prospectively. Sixty-three patients had 1 month's follow-up or longer, and this comprised the study group. In addition, histopathologic findings from 18 eyes of 9 patients were studied at autopsy.

INTERVENTION

A total of 296 injections of 20 microg cidofovir were given in 115 eyes. Sixty-three patients who had 246 injections in 93 eyes had 1 month's follow-up or longer for the evaluation of adverse events.

MAIN OUTCOME MEASURES

Postinjection chronic hypotony associated with permanent visual loss, transient hypotony, iritis, and its long-term sequela (posterior synechia and cataract, retinal detachment, extraocular cytomegalovirus involvement) were the outcomes of interest in this study. Additionally, light and electron microscopic studies of human eyes were performed.

RESULTS

The most severe adverse event was postinjection chronic hypotony. This phenomenon was associated with permanent visual loss. This was observed in 1% of the injections and 3% of the eyes of the patients (95% confidence interval, 0%-6%). Transient hypotony associated with mild-to-moderate visual loss developed in 14%, but vision recovered to baseline levels in these eyes subsequently. Analysis showed that transient hypotony in the injected eye could predict postinjection chronic hypotony in the fellow eye (two-tailed Fisher's exact test, P = 0.02). The incidence of iritis was 32%; posterior synechia and cataract were the long-term sequela of the iritis and developed in 19% and 11% of the eyes, respectively. The incidence of retinal detachment was lower (6%). Histopathologic evaluation of the eyes showed mild-to-moderate atrophy of the nonpigmented epithelium of the ciliary body and no other evidence of intraocular toxicity.

CONCLUSIONS

The most serious adverse event was postinjection chronic hypotony, which occurred in 3% of eyes. Episodes of transient hypotony appear to indicate that the fellow eye was predisposed to chronic hypotony. Therefore, it may be prudent to give intravitreous injections at least 2 weeks apart in the fellow eye to evaluate the clinical response of the injected eye.

Expression of HGF and cMet in the developing and adult brain

Hepatocyte growth factor (HGF) was recently recognized as a potential neurotrophic factor in the developing brain. We studied expression of HGF and its receptor using Northern blot analysis and in situ hybridization for mRNA and double immunofluorescent laser confocal microscopy. HGF and cMet messages were abundant in the hippocampus of both human and rat brains. In this region, both messages were localized in the neuronal layer. Segregation of HGF predominantly in the hippocampal CA3-4 and cMet in CA1 supports the hypothesis that HGF may mediate important neurotrophic functions in both developing and adult brains.

Evaluation of retinal toxicity and efficacy of anti-cytomegalovirus and anti-herpes simplex virus antiviral phosphorothioate oligonucleotides ISIS 2922 and ISIS 4015

Retinal toxicity of ISIS 2922 and ISIS 4015, phosphorothioate oligonucleotides complementary to human cytomegalovirus (CMV) and herpes simplex virus (HSV) RNA, were evaluated. The intravitreal concentration of ISIS 2922 found not to cause permanent toxic changes in the rabbit retina was 10 microM and in the pig retina, 5 microM. The 3 microM concentration was associated with a transient inflammatory response, and 1 microM caused no retinal toxicity or inflammation. ISIS 4015 showed very mild toxicity with no permanent retinal changes and very mild inflammation at doses of 10 microM; this dose was effective in ameliorating or preventing HSV-1 retinitis when injected 1 day and 1 week prior to virus inoculation. These oligonucleotides have a low intraocular therapeutic index. Attempts to improve the therapeutic index of these compounds are indicated. Only a clinical trial can determine the toxicity profile of ISIS 2922 for the treatment of CMV retinitis.

An animal model for cidofovir (HPMPC) toxicity: intraocular pressure and histopathologic effects

Intravitreal cidofovir has been shown to be a long acting and highly efficacious treatment for CMV retinitis; however decrease in IOP is an adverse effect. We wanted to determine the effect of cidofovir on intraocular pressure (IOP) in the guinea pig, and rabbit eye to develop an animal model of cidofovir induced ocular hypotony and to study the histopathology of this toxicity. Twenty-eight guinea pig eyes were injected with cidofovir yielding final intravitreal concentrations of 25, 200, 625 and 2000 micrograms ml-1. Eighteen eyes of pigmented rabbits were injected with cidofovir yielding final intravitreal concentrations of 625 and 2000 micrograms ml-1. A carefully calibrated low volume displacement manometer system using a micro-transducer was used to determine the IOP measurements in the guinea pig and rabbit eyes. Histology was evaluated using light and electron microscopy. Injection of 6.25 micrograms of cidofovir intravitreally (vitreous concentration of 25 micrograms ml-1) is the highest non-toxic dose in the guinea pig; the IOP was unchanged at two and four weeks after injection with this dose; histologically the eyes were normal. A single injection of 50 micrograms of cidofovir intravitreally (vitreous concentration of 200 micrograms ml-1) caused a long lasting (9.3 mmHg) decrease in IOP (approximately 50% of baseline). At this dose there were only mild and variable histologic changes in the ciliary body and the retina. Higher doses of 156.25 micrograms and 500 micrograms of cidofovir (vitreous concentrations of 625, and 2000 micrograms ml-1, respectively) caused moderate to severe ciliary body and retinal changes. In rabbit eyes there was a mild but statistically insignificant pressure drop with doses of 875 micrograms cidofovir intravitreally (vitreous concentration of 625 micrograms ml-1); retina was within normal limits after injection with this dose, there were mild changes in the ciliary body. There was a total destruction of ciliary body and loss of nonpigmented epithelial cells with injections of 2800 micrograms of cidofovir intravitreally (vitreous concentration of 2000 micrograms ml-1): retina was relatively well preserved. The guinea pig eye shows similar reduction in IOP and ciliary body changes as are seen in the human eye after intravitreal cidofovir and also appears to have a similar dose-response curve. However, the reduction of IOP caused by cidofovir occurs in the guinea pig eye at a concentration 40 times higher than was observed in the human eye.

Optic neuropathy preceding acute retinal necrosis in acquired immunodeficiency syndrome

OBJECTIVE

To describe the clinical course of varicella-zoster optic neuropathy preceding acute retinal necrosis in patients with acquired immunodeficiency syndrome.

DESIGN

Case series.

SETTING

Two tertiary care centers in San Diego, Calif, and London, England.

PATIENTS

Three human immunodeficiency virus-positive men with previous cutaneous zoster infection, optic neuropathy, and necrotizing retinitis.

RESULTS

All patients had an episode of zoster dermatitis treated with acyclovir. Visual loss consistent with an optic neuropathy ensued, followed by typical herpetic retinitis. The cause of visual loss was not suspected to be varicella-zoster until after the retinitis occurred. Despite aggressive medical treatment, 4 of 6 eyes progressed to retinal detachment.

CONCLUSIONS

Varicella-zoster may cause an optic neuropathy in patients with acquired immunodeficiency syndrome, especially in those with previous shingles. A high index of suspicion is necessary to establish the diagnosis and begin early antizoster treatment.

Human microglia convert l-tryptophan into the neurotoxin quinolinic acid

Immune activation leads to accumulations of the neurotoxin and kynurenine pathway metabolite quinolinic acid within the central nervous system of human patients. Whereas macrophages can convert L-tryptophan to quinolinic acid, it is not known whether human brain microglia can synthesize quinolinic acid. Human microglia, peripheral blood macrophages and cultures of human fetal brain cells (astrocytes and neurons) were incubated with [13C6]L-tryptophan in the absence or presence of interferon gamma. [13C6]Quinolinic acid was identified and quantified by gas chromatography and electron-capture negative-chemical ionization mass spectrometry. Both L-kynurenine and [13C6]quinolinic acid were produced by unstimulated cultures of microglia and macrophages. Interferon gamma, an inducer of indoleamine 2,3-dioxygenase, increased the accumulation of L-kynurenine by all three cell types (to more than 40 microM). Whereas large quantities of [13C6]quinolinic acid were produced by microglia and macrophages (to 438 and 1410 nM respectively), minute quantities of [13C6]quinolinic acid were produced in human fetal brain cultures (not more than 2 nM). Activated microglia and macrophage infiltrates into the brain might be an important source of accelerated conversion of L-tryptophan into quinolinic acid within the central nervous system in inflammatory diseases.

Clinicopathologic correlations in acute retinal necrosis caused by herpes simplex virus type 2

The acute retinal necrosis syndrome is a rapidly progressive and potentially devastating disease. A case of acute retinal necrosis developed in an immunocompetent man, Presumably due to the stress, trauma, or immunomodulation related to a craniotomy for a parasellar craniopharyngioma. Vitrectomy and endoretinal biopsy were performed. Polymerase chain reaction studies of the vitreous revealed herpes simplex virus type 2 as the cause, which has not been previously well documented. Results of cerebrospinal fluid antibody studies were also consistent with the diagnosis. Results of cytology and histopathologic examination demonstrated extensive retinal destruction and mononuclear cell infiltration. Sloughing of the inner retina was evidenced by the presence of retinal vascular remnants in the vitreous cytology specimen. As is characteristic of this disease, the visual outcome of this patient was poor.

Pathogenic and protective correlates of T cell proliferation in AIDS. HNRC Group. HIV Neurobehavioral Research Center

To investigate the association of antigen specific CD4 T cell activation with HIV disease progression and AIDS-related central nervous system damage, T cell proliferation responses to HIV, CMV, and HSV were evaluated in infected individuals. CD4 T cell loss and neurocognitive impairment were assessed at 6-mo intervals. Individuals with known times of seroconversion who responded to more HIV peptides were at greater risk of progressing to < 200 CD4 T cells (P = 0.04) and dying (P = 0.03) than those with responses to fewer peptides. A positive correlation (0.52) was seen between the breadth of the HIV proliferation response and HIV plasma RNA levels. Higher proliferation responses to CMV and HSV were also associated with more rapid CD4 loss (P = 0.05). HLA phenotyped individuals (n = 150) with two HLA-DR alleles associated with response to more HIV peptides and CMV (DR-2,5,w6,10) were less likely to develop neurocognitive (P = 0.002) and neurologic impairment (P = 0.04), but were not protected from CD4 loss and death. Thus, the ability to generate a greater T cell proliferation response to HIV and opportunistic herpes viruses may lead to resistance to central nervous system damage, but also risk of more rapid HIV disease progression.