Related Experiment Videos
Proliferating cellular nuclear antigen expression as a marker of perivascular macrophages in simian immunodeficiency
Kenneth Williams1, Annette Schwartz, Sarah Corey
1Department of Medicine, Harvard Medical School, Division of Viral Pathogenesis, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA. kenneth_williams@hms.harvard.edu
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 non-dividing cells undergoing DNA synthesis and repair. Therefore, more specific markers for cell proliferation including Ki-67, topoisomerase IIalpha, 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.
Insights
Brain perivascular macrophages are preferentially infected by SIV, the virus causing AIDS in macaques. These macrophages, distinct from microglia, are non-dividing cells, suggesting unique infection mechanisms in neuroAIDS.
Area of Science:
- Neuroscience
- Immunology
- Virology
Background:
- Brain perivascular macrophages are key targets for simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV).
- Perivascular macrophages differ from parenchymal microglia in the central nervous system (CNS) regarding location, morphology, myeloid markers, and cell turnover.
- Perivascular macrophages are replenished by blood monocytes, which mature into macrophages within the CNS.
Purpose of the Study:
- To investigate in vivo differences in monocyte/macrophage populations that may explain the preferential SIV infection of perivascular macrophages.
- To characterize the proliferation status of SIV-infected cells in the CNS and other tissues.
Main Methods:
- In situ hybridization for SIV and immunohistochemistry for proliferating cell nuclear antigen (PCNA).
- Multilabel techniques including double-label immunohistochemistry and combined in situ hybridization and immunofluorescence confocal microscopy.
- Specific proliferation markers (Ki-67, topoisomerase IIalpha, bromodeoxyuridine incorporation) were used to assess cell division.
Main Results:
- SIV-infected and PCNA-positive cells were concentrated in perivascular cuffs and SIV encephalitis (SIVE) lesions in viremic animals.
- Numerous SIV-infected perivascular macrophages were found to be PCNA-positive.
- Further analysis using specific proliferation markers revealed that PCNA-positive cells in SIVE lesions were not actively proliferating, indicating they are terminally differentiated.
- SIV-infected macrophage subpopulations expressing PCNA were also identified in the small intestine and lung.
Conclusions:
- Perivascular macrophages in the CNS are terminally differentiated, non-dividing cells.
- Biological differences in perivascular macrophages may underlie their preferential and productive infection by SIV.
- Subpopulations of SIV-infected macrophages expressing PCNA exist in both CNS and non-CNS tissues.