Proliferating Cellular Nuclear Antigen Expression as a Marker of Perivascular Macrophages in Simian Immunodeficiency Virus Encephalitis

Abstract

Brain perivascular macrophages are a major target of simian immunodeficiency virus (SIV) infection in rhesus macaques and HIV infection in humans.Perivascular macrophages are distinct from parenchymal microglia in their location, morphology, expression of myeloid markers, and turnover in the CNS. In contrast to parenchymal microglia, perivascular macrophages are continuously repopulated by blood monocytes, which undergo maturation to macrophages on entering the central nervous system (CNS). We studied differences in monocyte/macrophages in vivo that might account for preferential infection of perivascular macrophages by SIV. In situ hybridization for SIV and proliferating cellular nuclear antigen (PCNA) immunohistochemistry demonstrated that SIV-infected and PCNA-positive cells were predominantly found in perivascular cuffs of viremic animals and in histopathological lesions that characterize SIV encephalitis (SIVE) in animals with AIDS. Multilabel techniques including double-label immunohistochemistry and combined in situ hybridization and immunofluorescence confocal microscopy revealed numerous infected perivascular macrophages that were PCNA-positive. Outside the CNS, SIV-infected, PCNA-expressing macrophage subpopulations were found in the small intestine and lung of animals with AIDS. While PCNA is used as a marker of cell proliferation it is also strongly expressed in nondividing cells undergoing DNA synthesis and repair. Therefore, more specific markers for cell proliferation including Ki-67, topoisomerase II␣, and bromodeoxyuridine (BrdU) incorporation were used which indicated that PCNA-positive cells within SIVE lesions were not proliferating. These observations are consistent with perivascular macrophages as terminally differentiated, non-dividing cells and underscores biological differences that could potentially define mechanisms of preferential, productive infection of perivascular macrophages in the rhesus macaque model of neuroAIDS. These studies suggest that within CNS and non-CNS tissues there exist subpopulations of macrophages that are SIV-infected and express PCNA.

Macrophage/Microglial Accumulation and Proliferating Cell Nuclear Antigen Expression in the Central Nervous System in Human Immunodeficiency Virus Encephalopathy

“…In support of these findings, PCNAϩ, but Ki-67Ϫ, MPs were found to be abundant in SIV-infected macaques with encephalitis (SIVE). 32 The overall increase in the number of perivascular and parenchymal MPs we observed in this study supports a model in which both perivascular and parenchymal reservoirs of HIV-1 infection accumulate as a result of increased trafficking and CNS invasion. These results emphasize the role of invading macrophages and new resident microglia as major contributors to the active reservoir of HIV-1 infection in HIVE CNS tissue.…”

“…33 In our study, HIV-1 infection was clearly associated with PCNA expression in CNS, in agreement with a similar study in SIVE reported by Williams and colleagues. 32 PCNA/p24 double-labeling revealed that all cells positive for p24 were PCNAϩ. In contrast, not all PCNA-expressing cells appeared to be productively infected, in which no more than half of the PCNAϩ cells also had detectable levels of HIV-1 p24.…”

Cellular demise and inflammatory microglial activation during β-amyloid toxicity are governed by Wnt1 and canonical signaling pathways

“…In Fig. 3B, representative microglial cultures illustrate a marked induction of microglial activation and proliferation during treatment with Aβ 1-42 exposed media from SH-SY5Y wildtype cells (Aβ ) as evidenced by significant PCNA expression [24] and BrdU uptake [25] when compared to microglia treated with media not exposed to Aβ 1-42 (Control). Minimal activation (PCNA) or proliferation (BRDU) of microglia is present during treatment with media from SH-SY5Y cells overexpressing Wnt1 (Wnt1/Aβ ) which are also absent of membrane PS exposure (Fig.…”

Cell Tropism of Simian Immunodeficiency Virus in Culture Is Not Predictive of in Vivo Tropism or Pathogenesis

“…[13][14][15]31 After in situ hybridization for viral nucleic acid as described above, single-or double-label immunohistochemistry or immunofluorescence was performed using a variety macrophage-and T lymphocyte-specific markers (Table 2). …”