Direct ex vivo flow cytometric analysis of human microglial ... : AIDS (original) (raw)

ARTICLE

examination of central nervous system biopsy specimens from HIV-seropositive patients and patients with other neurological disease

Dick, Andrew D.1,4; Pell, Malcolm2; Brew, Bruce J.3; Foulcher, Eléna1; Sedgwick, Jonathon D.1,5

1Immunopathology Research Group, Centenary Institute of Cancer Medicine and Cell Biology, Royal Prince Alfred Hospital, Sydney, NSW Australia

2Department of Neurosurgery, St Vincents Hospital, Sydney, NSW Australia

3Department of Neurology and Centre for Immunology, St Vincents Hospital, Sydney, NSW Australia.

4Present address: Department of Ophthalmology, University of Aberdeen, Aberdeen, Scotland, UK.

5Requests for reprints to: Dr J.D. Sedgwick, Centenary Institute of Cancer Medicine and Cell Biology, Building 93, Royal Prince Alfred Hospital, Missenden Road, Camperdown, Sydney, NSW 2042, Australia.

Sponsorship: The studies were supported by grants to J.D.S. from The National Health and Medical Research Council and The National Multiple Sclerosis Society of Australia, to J.D.S. and B.J.B. from The Commonwealth AIDS Research Grants Scheme, and to A.D.D. from the Leverhulme Trust, UK; A.D.D. was a Wernher-Pigott MRC Travelling Fellow. These studies were performed while J.D.S. was a recipient of a Wellcome Trust Senior Research Fellowship in Medical Sciences in Australia.

Date of receipt: 18 February 1997; revised: 4 July 1997; accepted: 15 July 1997.

Abstract

Objective:

To define a clear ex vivo flow cytometric phenotype for adult human microglia that would distinguish it from all other macrophage lineage cells in the central nervous system (CNS) or blood, and to utilize this phenotype to examine the activation state and CD4 expression of microglia freshly derived from CNS tissue of HIV-positive patients and those with other neurological diseases.

Design:

Fresh human CNS tissue from both HIV-uninfected and HIV-infected individuals was obtained by biopsy or resection, and cells isolated immediately, labelled for flow cytometry and analysed.

Methods:

A Percoll density gradient isolation technique and phenotypic characteristics used for rodent microglia were applied and modified.

Results:

Resident microglia could clearly be defined by the flow cytometric phenotype CD45low CD4−CD11b+ CD11chigh major histocompatibility complex (MHC) class II+ CD26− CD14−. Assuming normally low-level MHC class II expression in the healthy CNS, it was likely that MHC class II positivity reflected underlying pathology necessitating biopsy or resection and appeared to be a ‘leaky’ activation marker. Microglia activation was observed in specimens from only six (35%) out of 17 HIV-uninfected but all four (100%) HIV-infected patients, defined strictly as any level of upregulation of CD4 expression, to produce the phenotype CD45low/medium CD4low CD11b+ CD11chigh MHC class II+/++ CD26− CD14−. Where examined by immunohistology, CD68 was also upregulated in these cases.

Conclusions:

When activated in situ, microglia express low levels of CD4 and this is always seen in tissue from HIV-infected patients. Using the flow cytometric phenotype established here, microglia from HIV-infected tissue can now be isolated in pure form and studied directly ex vivo.