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. 2012 Aug;86(16):8507-15.
doi: 10.1128/JVI.00598-12. Epub 2012 May 30.

Efficient human cytomegalovirus reactivation is maturation dependent in the Langerhans dendritic cell lineage and can be studied using a CD14+ experimental latency model

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Efficient human cytomegalovirus reactivation is maturation dependent in the Langerhans dendritic cell lineage and can be studied using a CD14+ experimental latency model

Margaret M Huang et al. J Virol. 2012 Aug.

Abstract

Studies from a number of laboratories have shown that the myeloid lineage is prominent in human cytomegalovirus (HCMV) latency, reactivation, dissemination, and pathogenesis. Existing as a latent infection in CD34(+) progenitors and circulating CD14(+) monocytes, reactivation is observed upon differentiation to mature macrophage or dendritic cell (DC) phenotypes. Langerhans' cells (LCs) are a subset of periphery resident DCs that represent a DC population likely to encounter HCMV early during primary infection. Furthermore, we have previously shown that CD34(+) derived LCs are a site of HCMV reactivation ex vivo. Accordingly, we have utilized healthy-donor CD34(+) cells to study latency and reactivation of HCMV in LCs. However, the increasing difficulty acquiring healthy-donor CD34(+) cells--particularly from seropositive donors due to the screening regimens used--led us to investigate the use of CD14(+) monocytes to generate LCs. We show here that CD14(+) monocytes cultured with transforming growth factor β generate Langerin-positive DCs (MoLCs). Consistent with observations using CD34(+) derived LCs, only mature MoLCs were permissive for HCMV infection. The lytic infection of mature MoLCs is productive and results in a marked inhibition in the capacity of these cells to promote T cell proliferation. Pertinently, differentiation of experimentally latent monocytes to the MoLC phenotype promotes reactivation in a maturation and interleukin-6 (IL-6)-dependent manner. Intriguingly, however, IL-6-mediated effects were restricted to mature LCs, in contrast to observations with classical CD14(+) derived DCs. Consequently, elucidation of the molecular basis behind the differential response of the two DC subsets should further our understanding of the fundamental mechanisms important for reactivation.

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Figures

Fig 1
Fig 1
Differentiation of CD14+ monocytes with TGF-β promotes a Langerhans-like phenotype. (A) Freshly isolated monocytes were characterized for CD14+, CD83, and CD207 expression. (B) Light microscopy of freshly isolated monocytes or monocytes cultured for 6 days in IL-4/GM-CSF or IL-4/GM-CSF/TGF-β to promote the formation of a DC (MoDC)- or an LC (MoLC)-like cell type. (C) MoDCs, MoLCs, or Langerhans cells generated from CD34+ precursors (CD34+ LCs) were analyzed by flow cytometry for class I, class II, CD1a, CD207, and E-Cadherin expression.
Fig 2
Fig 2
A clinical isolate of HCMV infects immature LCs inefficiently. (A) MoLCs and DCs were infected with TB40/e (columns 1 to 4) or Toledo (columns 5 to 8) before (iDC and iLC) or after (mDC and mLC) LPS stimulation and analyzed for IE gene expression by immunofluorescence microscopy at 24 h postinfection. The percent infection was calculated from four fields per well from an analysis performed in triplicate. (B) MoLCs and DCs were infected with TB40/e before (iDC and iLC) or after (mDC and mLC) LPS stimulation and analyzed by PCR 24 h postinfection for IE72 and GAPDH RNA expression and the presence of viral genomes.
Fig 3
Fig 3
TGF-β does not directly inhibit HCMV infection of immature DCs. CD14+ derived DCs were either not stimulated (columns 1 and 3) or stimulated with TGF-β (columns 2 and 4) for 30 min prior to HCMV infection. The cells were then infected at either a low (columns 1 and 2) or a high (columns 3 and 4) MOI and then assayed for infection by immunofluorescence microscopy at 24 h postinfection.
Fig 4
Fig 4
Mature MoLCs support the complete replicative cycle of HCMV. (A) Mature MoLCs were either mock (lanes M) or TB40/e (lanes V) infected and then analyzed by Western blotting for IE, gB, and GAPDH expression at 24 and 72 h postinfection (hpi). (B and C) Mature CD14+ derived DCs (MoDC) or LCs (MoLC) were infected with TB40/e and then analyzed every 2 days for virus production in the supernatant. Alternatively, at 7 days postinfection both the supernatant (cell-free) and the lysed cells (cell-associated) were assayed for infectious virus.
Fig 5
Fig 5
Infected mature MoLCs are impaired in their ability to promote T cell proliferation in a mixed leukocyte reaction. MoLCs were either mock infected (black) or HCMV infected (gray), followed by incubation, at 72 h postinfection, with 8 × 104 T cells at the E:T ratio shown. The T cell proliferation was assayed for the total cell count from triplicate wells. The results shown are representative of four independent repeats.
Fig 6
Fig 6
Efficient reactivation of HCMV from MoLCs is maturation dependent and enhanced by IL-6. (A) CD14+ monocytes TB40/e (lanes 1 and 2) or mock (lanes 3 and 4) infected were analyzed for RNA expression at 3 days postinfection. RNA with (+) or without (−) prior RT was amplified in UL138, IE72, and actin-specific PCRs. For the IE72 PCR, an HCMV DNA PCR-positive control was included to confirm that the PCR had worked (lane 5). (B) RNA isolated from immature MoLCs either mock treated (lane 1) or treated with IL-6 (lane 2), IL-8 (lane 3), LPS (lane 4), LPS plus neutralizing IL-6 antibody (lane 5), or LPS plus neutralizing IL-8 antibody (lane 6) was (+) or was not (−) subjected to RT and then amplified in an IE72 or actin PCR. (C and D) MoLCs were cocultured with fibroblasts to assay HCMV reactivation. After 10 days, the cultures were analyzed for evidence of plaque formation (C) and HCMV reactivation by inoculating fresh monolayers of fibroblasts with 50 μl of the supernatant and staining for IE gene expression 24 h postinfection as an indicator of infectious virus in the supernatant (D).
Fig 7
Fig 7
Efficient reactivation of HCMV from CD34+ derived LCs is maturation dependent and is responsive to IL-6. (A) CD34+ derived immature LCs either mock treated (column 1) or cultured with LPS (column 2), IL-6 at 5 to 50 ng/ml (columns 3 and 5), or LPS plus IL-6 at 5 to 50 ng/ml (columns 4 and 6) and then analyzed for IE and actin gene expression by real-time quantitative RT-PCR. The results are expressed as the fold change in IE gene expression compared to LPS alone. (B) CD34+ derived immature LCs were either mock treated (column 1) or incubated with LPS (column 2), LPS plus neutralizing IL-6 antibody (IL6; columns 3, 5, and 7), or isotype-matched control (IgG; columns 4, 6, and 8) and analyzed by quantitative RT-PCR for IE and actin gene expression. Reactivation is expressed as a function of LPS alone (100%).
Fig 8
Fig 8
Reactivation of naturally latent HCMV is observed in LCs derived from CD14+ and CD34+ progenitor cells. (A) CD14+ cells isolated from CMV-seropositive and -seronegative donors were differentiated to immature LCs and then either mock treated (lane 1) or incubated with LPS (lane 2), LPS plus 50 ng of IL-8/ml (lane 3), or LPS plus 50 ng of IL-6/ml (lane 4) and analyzed for IE and actin gene expression by RT-PCR (n = 4). (B) CD34+ cells isolated from CMV-seropositive and -seronegative donors were differentiated to immature LCs and then either mock treated (lane 1) or incubated with LPS (lane 2), LPS plus 1 μg of nIL6ab/ml (lane 3), LPS plus 1 μg of nIL8ab/ml (lane 4), LPS plus 50 ng of IL-6/ml (lane 5), or LPS plus 50 ng of IL-8/ml (lane 6) and then analyzed for IE and actin gene expression by RT-PCR (n = 4).

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