Giant cell encephalitis and microglial infection with mucosally transmitted simian-human immunodeficiency virus SHIVSF162P3N in rhesus macaques

Abstract

Neurocognitive disorders such as dementia and cognitive/motor impairments are among the most significant complications associated with human immunodeficiency virus (HIV) infection, especially in aging populations, yet the pathogenesis remains poorly understood. Activated macrophages and microglia in white matter along with the hallmark multinucleated giant cells are prominent features of HIV encephalitis (HIVE) and of several simian immunodeficiency virus (SIV) models. While infected microglia have been demonstrated in HIVE, this feature is not routinely seen in experimental infections in rhesus macaques using SIV or chimeric simian/HIV (SHIV) strains, limiting utility in HIV-1 pathogenesis and treatment studies. Here, 50 rhesus macaques were inoculated with the CCR5 (R5)-tropic SHIVSF162P3N virus by one of three routes: intravenously (n = 9), intrarectally (n = 17), or intravaginally (n = 24). Forty-three monkeys became viremic, 26 developed AIDS, and 7 (7/26, 27 %) developed giant cell SIV encephalitis (SIVE). Rapid progressor phenotype was evident in five of seven (71 %) macaques with SIVE, and expansion to utilize the CXCR4 coreceptor (X4 coreceptor switch) was observed in four out of seven (57 %). SIVE lesions were present in gray and white matter in the cerebrum, cerebellum, thalamus, and brain stem of affected animals. Lesions were composed of virally infected CD68(+), CD163(+), and HLA-DR(+) macrophages accompanied by white matter damage, necrosis, and astroglial and microglial activation. Importantly, microglial infection was observed, which makes R5 SHIVSF162P3N infection of macaques an attractive animal model not only to study transmission and HIVE pathogenesis but also to conduct preclinical evaluation of therapeutic interventions aimed at eradicating HIV-1 from the central nervous system (CNS).

Fig. 1

Virologic and immunologic parameters of SHIV_SF162P3N infection. Temporal analysis of viral load (a) and peripheral CD4⁺ T cell counts (b) in the plasma of macaques with SIVE. Dagger indicates time of euthanasia. Peak plasma (c) and end-stage CSF (d) viral load in infected rhesus macaques that progressed to AIDS, divided as those with SIVE (plus sign) and those without SIVE (minus sign). Solid symbols in c and d designate rapid progressors

Fig. 2

Neuropathologic features of SIVE in brains of R5 SHIV_SF162P3N-infected macaques. a–c Perivascular histiocytic lesions (case ET94, frontal cortex) are positive for SIV by ISH (a), and CD68 (b) and CD163 (c) by immunohistochemistry with frequent multinucleated giant cells surrounded by activated microglia observed. d–f Severe parenchymal lesions with white matter damage (case ET94, thalamus) also contain SIV⁺ (d), CD68⁺ (e), and CD163⁺ (f) cells with gemistocytic astrocytes and occasional neutrophils. g–i In chronic burnt-out lesions (case ET94, occipital cortex), infected cells contain a scant amount of virus by SIV ISH (g), but abundant CD68 (h) and CD163⁺ (i) cells invade deeply into the surrounding parenchyma. j Microglia with rod-shaped nuclei are infected in all three types of lesions (SIV ISH⁺). k, l Activated microglia. k Iba-1-positive and l CD163-positive activated microglia are located distant from the center of a perivascular lesion. Luxol fast blue (LFB) staining of myelin is decreased in severe parenchymal lesion (m), lesion in the white matter tract (n), and in burnt-out lesion with phagocytosed myelin within macrophages (o)

Fig. 3

Microglial and astroglial activation in R5 SHIV_SF162P3N-infected macaques. Brain sections were analyzed by immunohistochemistry for activated microglia (Iba-1, a–c) and astrocytes [glial fibrillary acidic protein (GFAP), d–f]. Low magnification images demonstrate an extent of microglial (a) and astroglial (d) activation (original magnification, ×4). Extensive microglial activation exhibited by upregulated Iba-1 and microglial nodule (b) and amoeboid morphology (c) (original magnification, ×20). Higher magnification of GFAP⁺-activated astrocytes around a discrete lesion (e, original magnification, ×20) and throughout a large expansive region (f, original magnification, ×10)

Fig. 4

Characterization of R5 SHIV_SF162P3N-infected macrophage subpopulations and microglia. Immunofluorescence and confocal laser microscopy of CD68⁺ (a–c), CD163⁺ (d–f), Mac387⁺ (g–i), and HLA-DR⁺ (j–l) macrophage/microglia in the brain. An infected CD68⁺ microglia in a perineuronal location in the gray matter (m–o). a, d, g, j, m SIV p27 protein (green). b, n CD68 (red). e CD163 (red). h Mac387 (red). k HLA-DR (red). c, f, i, l, o Overlay with glut1 endothelial marker (blue) and colocalization of infected macrophages (yellow, c, f, i, l) or microglia (o). a–f, m–o Original magnification, ×80. g–l Original magnification, ×40