Elsevier

The Lancet

Volume 348, Issue 9028, 7 September 1996, Pages 649-654
The Lancet

Early Report
Frequent infection of peripheral blood CD8-positive T-lymphocytes with HIV-1

https://doi.org/10.1016/S0140-6736(96)02091-0Get rights and content

Summary

Background

Although lymphocytes expressing the CD4 surface receptor for HIV-1 have been identified as the principal target of the virus, the extent to which infection of other cell types of the immune system contributes to immunodeficiency is unknown. We investigated the cell types in peripheral blood infected with HIV and the relation of viral load in different subsets to disease progression.

Methods

The study group consisted of 16 HIV-infected individuals, eight of whom had clinically defined AIDS with CD4 cell counts less than 200/μ, L blood. The main component subsets of peripheral blood mononuclear cells were purified by magnetic bead separation, and included CD4 and CD8 lymphocytes, B lymphocytes, monocytes, and dendritic cells. HIV proviral sequences within these separate populations were quantified by limiting-dilution nested polymerase chain reaction.

Findings

HIV-1 proviral sequences were detected in T-helper cells, cytotoxic T cells, dendritic cells, and monocytes. CD4 T lymphocytes constituted the main reservoir of HIV in all but one of the symptom-free individuals studied (those with CD4 count 200/μL). However, in all the individuals with CD4 counts of less than 200/μL, most infected cells within the peripheral blood mononuclear cell fraction were either dendritic cells or CD8 lymphocytes. Infection of CD8 cells accounted for between 66% and 97% of total proviral load in five of the eight AIDS patients. A strong inverse relation between total CD8 count and the frequency of CD8 T-lymphocyte infection was found.

Interpretation

This study provides evidence for widespread infection of lymphocytes of the CD8 phenotype, indicating that HIV-1 has a broader tropism for different cell types in vivo than described for cultured virus. Infection of CD8 cells may contribute to the decline of this subset upon disease progression in HIV-infected individuals. Infection of CD8 cells may or may not occur by a non-CD4-dependent mechanism of virus entry.

Introduction

The principal immunological defect occurring with progression of HIV-1 infection is the loss of CD4 T-helper cells, which have a central role in the immune response to pathogens. Theories about the causes of this loss of CD4 cells range from their destruction or dysfunction directly caused by viral infection to apoptosis resulting from defects in antigen presentation.1 Whether the defects in many immune pathways, including the cytotoxic T-cell response mediated by CD8 lymphocytes, are secondary to the destruction of T-helper lymphocytes is similarly unclear. For example, Macatonia and colleagues suggested that infection of reticulodendritic cells with HIV contributes to the defects in antigen processing and presentation to T-helper cells found in AIDS patients.2

In this study, we used standard separation methods to isolate subsets of cells involved in the immune response and thereby to investigate the extent to which each cell type is infected with HIV. It has hitherto been generally accepted that the cellular tropism of HIV is determined almost exclusively by the distribution of CD4, the cell-surface receptor for HIV-1.1, 2, 3 After virus attachment, high-affinityinteractionsbetweenCD4 and the external envelope glycoprotein (gp120) of HIV-1 initiate conformational changes, resulting in exposure of a fusogenic domain of the transmembrane envelope protein (gp41) which allows entry of the virus into the cytoplasm.1 CD4 is expressed on T-helper cells, monocytes, and peripheral-blood dendritic cells6, 7 but not on B cells or mature cytotoxic T cells.

Although monocytes express CD4 and the activation marker HLA-DR,1, 8, 9 there is little evidence for extensive infection of these cells with HIV. Estimates of the frequency of infected monocytes in the peripheral circulation have ranged from zero to 100 per million of total cells.10, 11, 12, 13, 14 Previous reports have found little evidence for in-vivo infection of mature cytotoxic T cells with HIV,10, 15 although infection of CD8 T lymphocytes has been achieved in vitro.6

Peripheral-blood dendritic cells, like monocytes, are a heterogeneous population at different stages of maturation.6 They are extremely potent antigen-presenting cells and their infection by HIV could be critical in the generation of immune dysfunction. Various groups have isolated populations of these cells that can be infected in vitro2, 16, 17 and HIV-1 has been isolated directly from peripheral-blood cells with dendritic-cell characteristics.14, 18

It is not known whether strains of HIV exist with differences in tropism for different cell types found in peripheral blood mononuclear cell populations. In vitro, macrophage tropism is associated with a non-syncytium-inducing viral (NSI) phenotype. Changes in phenotype and tropism of virus isolates are known to occur during disease progression19, 20, although no change in the relative frequencies of the different cell types infected has been shown. Although in-vitro studies19, 20 suggest that HIV isolated from patients with advanced immunodeficiency is unable to replicate in the monocyte lineage, we have found that disease progression is associated with the spread of HIV from cells of the lymphoid system to peripheral sites such as lung, brain, and gut,21 where many of the target cells in these tissues are of the macrophage/monocyte lineage, such as microglia in the brain.22

In this study, whole blood from HIV-1-positive individuals was separated into component cell populations and nucleic acid was extracted from CD4 T cells, CD8 T cells, monocytes, B cells, and dendritic cells. Limiting-dilution PCR was then used to quantify the amounts of provirus in each cell type.

Section snippets

Blood samples

20 mL samples of whole blood were collected from 16 HIV-seropositive individuals in Edinburgh, UK. Immunological and virological information on disease progression was available for 13 of the participants, whose risk factors for infection included intravenous drug abuse and sexual contact with an HIV-positive individual. CD4 counts were available for the samples studied and for the same individuals every 1 or 2 months during the previous 6 months, so mean values could be calculated. These

Results

ER-positive cells contained a mean frequency (three measurements) of 82·8% CD3 cells (table 2). Contaminating cells included B lymphocytes (0·9% CD 19 cells) and natural killer cells (15·5% CD16 cells). Positive selection for CD4 cells was shown by a reduction of CD4-positive cells from a mean of 47·0% in the ER-positive population to 1·7% in the depleted cells. CD4-depleted T cells consisted of 54–5% CD8 cells, which were then positively selected on CD8-coated beads. Residual cells after CD8

Discussion

We found HIV infection of a range of cell types within the peripheral blood mononuclear cell populations. There was remarkable variation in the frequencies of infected cells within each subset, although there was some evidence for a consistent change in the predominant CD4 T-helper target cells upon disease progression.

A surprising finding was the frequent infection of CD8 lymphocytes from AIDS patients (as high as 400 provirus copies per 106 cells in one case). For methodological reasons we

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