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MBio. 2019 May 28;10(3). pii: e00970-19. doi: 10.1128/mBio.00970-19.

Neuroinflammatory Changes in Relation to Cerebrospinal Fluid Viral Load in Simian Immunodeficiency Virus Encephalitis.

Author information

1
Center for Infectious Disease Imaging, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA hammoudd@cc.nih.gov.
2
Center for Infectious Disease Imaging, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA.
3
Division of Intramural Research, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
4
Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
5
Imaging Probe Development Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, Maryland, USA.
6
Biostatistics and Clinical Epidemiology Service, Clinical Center, National Institutes of Health, Bethesda, Maryland, USA.
7
Section of Infections of the Nervous System, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
8
AIDS Imaging Research Section, Division of Clinical Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, USA.

Abstract

The exact cause of neurocognitive dysfunction in HIV-positive patients despite successful control of the infection in the periphery is not completely understood. One suggested mechanism is a vicious cycle of microglial activation and release of proinflammatory chemokines/cytokines that eventually leads to neuronal loss and dysfunction. However, the exact role of microglial activation in the earliest stages of the infection with high cerebrospinal fluid (CSF) viral loads (VL) is unclear. In this study, we imaged the translocator protein (TSPO), a mitochondrial membrane receptor known to be upregulated in activated microglia and macrophages, in rhesus macaques before and multiple times after inoculation with a neurotropic simian immunodeficiency virus (SIV) strain (SIVsm804E), using 18F-DPA714 positron emission tomography (PET). The whole-brain standardized uptake values of TSPO at equilibrium reflecting total binding (SUVT) and binding potentials (BPND) were calculated and correlated with CSF and serum markers of disease, and a corresponding postmortem immunostaining analysis was also performed. SUVT was found to be inversely correlated with both CSF VL and monocyte chemoattractant protein 1 (MCP-1) levels. In SIV-infected macaques with very high CSF VL at necropsy (>106 copies/ml), we found decreased TSPO binding by PET, and this was supported by immunostaining which showed glial and neuronal apoptosis rather than microglial activation. On the other hand, with only moderately elevated CSF VL (∼104 copies/ml), we found increased TSPO binding as well as focal and diffuse microglial activation on immunostaining. Our results in the SIV-infected macaque model provide insights into the relationship between HIV neuropathology and CSF VL at various stages of the disease.IMPORTANCE Neurological and cognitive problems are a common complication of HIV infection and are prevalent even in treated individuals. Although the molecular processes underlying brain involvement with HIV are not completely understood, inflammation is suspected to play a significant role. Our work presents an in vivo assessment of neuroinflammation in an animal model of HIV, the simian immunodeficiency virus (SIV)-infected rhesus macaque. Using positron emission tomography (PET) imaging, we identified changes in brain inflammation after inoculation with SIV over time. Interestingly, we found decreased binding of the PET ligand in the presence of very high cerebrospinal fluid (CSF) viral loads. These findings were supported by immunostaining which showed marked glial loss instead of inflammation. This study provides insight into glial and neuronal changes associated with very high CSF viral load and could reflect similar changes occurring in HIV-infected patients.

KEYWORDS:

DPA714; SIV encephalitis; neuroinflammation; positron emission tomography; rhesus macaques; translocator protein

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