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1 Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523-1619, USA
2 Center for Biomedical Research, Population Council, 1230 York Avenue, New York, NY 10021, USA
Correspondence
Wendy S. Sprague
wsprague{at}lamar.colostate.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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; Milush et al., 2004; Stahl-Hennig et al., 1999; Zhang et al., 1999). In human immunodeficiency virus (HIV-1) and SIV infections, there is evidence that conjugates of cutaneous DC and T cells generate virus amplification in vitro (Pope et al., 1994, 1997); and HIV-1 replication in vivo has been demonstrated in syncytia derived from DC in lymphoepithelium of the tonsil adenoid mucosa (Frankel et al., 1996, 1997). Exactly how DC serve to amplify lentivirus infection remains the subject of current research. In vitro studies involving exposure of DC to HIV-1 have yielded varying results, postulated to relate to: (i) different DC subsets used (i.e. blood vs cultured DC), (ii) different DC isolation methods (i.e. antibody purification vs metrimazide gradient), (iii) different methods of viral detection (i.e. electron microscopy vs PCR) and (iv) different virus isolates (Blauvelt et al., 1997; Cameron et al., 1994; Granelli-Piperno et al., 1998; Patterson & Knight, 1987). However, what seems least controversial is that HIV-1 amplification occurs in DC/T-cell conjugates (Cameron et al., 1992; Pope et al., 1994, 1995). Recent work has questioned whether HIV-1 and SIV are captured by or replicated in DC. It has been proposed that lentivirus transfer to T cells occurs in two phases: (i) an immediate transfer of virus captured and internalized by DC and (ii) a more efficient transfer that requires de novo virus replication in immature DC (Frank et al., 2002; Turville et al., 2004). FIV is the feline counterpart of HIV-1 infection, and may therefore display a very similar mode of early infection pathogenesis. To investigate this point, we examined whether feline monocyte-derived DC can take up, replicate and/or transfer FIV to CD4+ T cells.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Generation of FIV supernatants.
The cell-free virus inoculum (8.89x104 TCID50 ml–1) was generated from co-culture of naïve feline PBMC, with PBMC from a cat intravenously infected with FIV clade C isolate Paddy Gammer (Sodora et al., 1994). Infectivity of the supernatants was determined by titration and aliquots were frozen at –70 °C.
Cell isolation and culture.
DC were cultured from CD14+ monocytes as described previously (Sprague et al., 2005). Since purity of DC cultures was needed for the infection studies, DC harvested after 6–7 days of culture were positively selected from contaminating lymphocytes using magnetic columns (Miltenyi Biotec) and a cross-reactive canine CD11c Ab (Leukocyte Antigen Laboratory, University of California, Davis, USA). Briefly, cells were blocked with 200 µl goat serum (Sigma-Aldrich), washed with PBS+0.5 % BSA and incubated with CD11c Ab (20 µl per 106 cells) for 20 min at 4 °C. Cells were washed again with PBS+0.5 % BSA and incubated with goat anti-mouse beads (20 µl per 106 cells) and placed in a magnetic column according to manufacturer's instructions (MS column; Miltenyi Biotec). CD4+ T cells were isolated from the negative fraction of the CD14+ selection and incubated with phycoerythrin (PE)-conjugated anti-feline CD4 (Southern Biotech) at 0.5 µl per 107 cells for 20 min at 37 °C. Cells were washed and incubated with anti-PE beads (Miltenyi Biotec) according to the manufacturer's directions and placed in a magnetic column (LS column; Miltenyi Biotec). The positive fraction was collected, cells were counted and then either frozen in liquid nitrogen, to produce a stock of unstimulated CD4+ T cells, or cultured in complete RPMI in the presence Concanavalin A (Con A; 5 µg ml–1) and interleukin (IL)-2 (100 U ml–1), to produce activated CD4+ T cells. Con A was added immediately to the cultures and replenished every 2 days with one half media changes and IL-2 (100 U ml–1) was added after the first 3 days and replenished with one half media changes.
Flow cytometry.
Phenotypic expression of CD11c+-purified feline DC was evaluated by flow cytometry as described previously (Sprague et al., 2005). DC purity was assessed using anti-feline CD4, anti-feline CD8 (Southern Biotech) and a cross-reactive anti-human CD21 (Pharmingen). Isotype-matched mouse immunoglobulins were used as controls. Cells were resuspended in flow buffer (PBS+0.5 % sodium azide+2 % FBS), propidium iodide was used to exclude dead cells from analysis and gating of large cells for analysis was determined by scatter properties using a Coulter Counter (EPICS XL-MCL; Beckman Coulter). Data was analysed with FlowJo software (Tree Star).
Inoculation of DC with FIV and virus co-culture.
Between 3x105 and 7x105 DC were placed into 15 ml centrifuge tubes (BD Falcon) in 500 µl complete RPMI. Cells were infected with 2–3x103 50 % TCID50. DC were incubated for 2 h at 37 °C and then washed four times to remove unbound virus. DC were cultured at 6.0x105 cells ml–1 in 200 µl complete RPMI in 96-well flat-bottomed plates (BD Falcon) for an additional 7 or 9 days. Unstimulated CD4+ T cells or activated CD4+ T cells were added immediately at DC : T cell ratios of 1 : 10 to some wells. In some experiments, activated CD4+ T cells were added after 2 days of DC infection and culture to assess if infection was from de novo FIV synthesis within DC. One-half of the medium was changed and cytokines were replenished every other day during the culture period.
Real-time DNA PCR for FIV.
DNA was extracted from DC or DC/T cell co-cultures after 7 or 9 days in culture using a QIAamp Mini kit (Qiagen). Quantitative real-time PCR (qPCR) was performed using previously published FIV CPGammar primer and probe sequences (Pedersen et al., 2001) and an iCycler iQ (Bio-Rad). qPCR was performed using 2x TaqMan Universal PCR Master Mix (Applied Biosciences) consisting of 10 mM Tris/HCl (pH 8.3), 50 mM KCl, 5 mM MgCl2, 300 µM each of dATP, dCTP and dGTP, 600 µM dUTP, 0.625 U AmpliTaq Gold DNA polymerase and 0.25 U uracil N-glycosylase (UNG) per reaction. Reactions were performed in a total volume of 25 µl and consisted of 12.5 µl Mastermix, 5 µl of sample or standard, 400 nM of each primer and 80 nM probe. Thermal cycling conditions were 2 min at 50 °C to induce enzymic activity of UNG, 10 min at 95 °C to reduce UNG activity and to activate AmpliTaq Gold DNA, followed by 40 cycles at 95 °C for 15 s and 60 °C for 1 min. A standard curve was generated with 10-fold serial dilutions of FIV C gag plasmid DNA with 1x TE and 40 ng salmon testes DNA (Sigma-Aldrich) ml–1 as a DNA carrier for each run and numbers of FIV C DNA viral copies were calculated from these curves. Statistical analysis was performed on paired samples using the Wilcoxon signed-rank test using Prism version 4.0b software for Macintosh (GraphPad).
FIV p26 ELISA.
Productive infection of DC or DC/T cell co-cultures was assessed by the FIV capsid antigen (Ag) p26 capture ELISA described previously by Dreitz et al. (1995). OD450 were recorded with a Dynatech 5000MRTM microplate reader (Dynatech). A minimum OD450 of 0.1 that was at least twice the value of negative control supernatants run in parallel defined the positive reactions. Statistical analysis was performed using the Student's t test.
Electron microscopy.
DC were pulsed with 8–9x104 TCID50 to maximize frequency of infection. DC pulsed with FIV for 2 h were washed with complete RPMI and immediately fixed with 2 % glutaraldehyde in PBS at 4 °C. Specimens were post-fixed in osmium tetroxide, dehydrated in acetone, and embedded in a 50 : 50 mixture of Epon 812 and Spurr resins, all using a rapid microwave technique described elsewhere (Leong & Sormunen, 1998). Ultrathin sections were mounted on nickel grids, contrasted with uranyl acetate and lead citrate, and examined using transmission electron microscopy (TEM) (JEOL 2000EXII).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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FIV viral particles are found within large DC vacuoles
DC were examined for virus uptake by TEM 2 h after inoculation and incubation at 37 °C. In the small minority of the cells that contained viral particles, virus was found within large membrane-bound intra-cytoplasmic vacuoles as seen in Fig. 1. Virus particles were similarly found in DC cultured from four different cats.
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). Only when activated CD4+ T cells were added to the DC was Ag detected; thereafter a steady increase in viral protein was noted through 7 days post-infection (p.i.). The p26 assay results correlated with the very low FIV DNA loads detected in DC alone and in DC co-cultured with unstimulated CD4+ T cells, whereas high viral DNA levels were detected in co-cultures of virus-exposed DC with activated CD4+ T cells. Statistically significant differences distinguished FIV protein expression in DC cultures alone [5 days p.i., P=0.0302; 7 days p.i., P<0.0001] and DC-unstimulated CD4+ T cell co-cultures (5 days p.i., P=0.0353; 7 days p.i., P<0.0001) versus DC-activated CD4+ T cell cultures.
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) in vitro. Therefore, to determine if transfer of infection was induced by de novo replication of FIV within DC, FIV-pulsed and washed DC were cultured for an additional 48 h prior to adding activated CD4+ T cells. Amplification of viral DNA was still apparent when activated CD4+ T cells were added 48 h after initial FIV-DC exposure, strongly suggesting that de novo replication of FIV had occurred (Fig. 4). Statistical analysis revealed a trend towards significance (P=0.0625) between FIV DNA viral loads in DC cultured alone versus those cultured with activated CD4+ T cells.
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). In contrast, a minimum of 9 days was required before p26 was detectable in supernatants of DC cultured alone, suggesting that the virus replicates slowly at low levels in these cells. Increase in DC FIV DNA loads over time supports de novo replication
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). This correlates with the detection of p26 in culture supernatants by day 9 noted in Fig. 5
and further supports low level de novo replication. However, statistical significance was not reached and this was likely to be due to low sample numbers (n=4).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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; Lore et al., 2005; McDonald et al., 2003; Turville et al., 2004; Wiley & Gummuluru, 2006). To understand the events involved in the initial contact of FIV with purified immature feline DC, FIV-pulsed and washed DC were examined for virus uptake. Uptake of FIV viral particles into large cytoplasmic vacuoles was evident by 2 h post-incubation, comparable to that seen in SIV and HIV-1 (Blom et al., 1993; Frank et al., 2002; Wiley & Gummuluru, 2006). In addition, the low viral DNA levels found in feline DC exposed to FIV for 2 h, then washed and recultured for 7 days strongly parallel the results reported by Turville et al. (2004, 2005) regarding HIV-1-exposure of immature human DC. We did observe higher DC viral DNA levels in a few animals. While this could have been due to lymphocyte contamination, lymphocytes were not detected by flow cytometry or light microscopy, and the differing DNA levels could reflect individual variation among cats.
When unstimulated CD4+ T cells were added to the FIV-exposed and washed DC followed by co-culture for 7 days, only slight amplification of viral DNA was detected. While it has been shown previously that highly purified unstimulated CD4+ T cells cannot be infected with HIV-1 in vitro (Ignatius et al., 1998; Stevenson et al., 1990; Zack et al., 1992), modest enhancement of virus replication was noted in DC-unstimulated CD4+/T cell co-cultures (Weissman et al., 1996). In addition, it has been shown that IL-4, which was added to our co-cultures, enhances replication in both purified unstimulated CD4+ T cells and in DC-unstimulated CD4+ T cell co-cultures (Unutmaz et al., 1999; Weissman et al., 1996). Most prominent in our studies was the marked increase in viral DNA loads observed after co-culture of activated CD4+ T cells with FIV-pulsed DC. This result correlates with previous in vitro and in vivo studies demonstrating amplified HIV and SIV production in activated CD4+ T cells (Cameron et al., 1992; Granelli-Piperno et al., 1998; Zhang et al., 1999).
The lack of detectable FIV capsid protein and low viral DNA levels in immature DC cultured alone and in DC-unstimulated CD4+/T cell co-cultures is consistent with the results of a study by Messmer et al. (2000) that demonstrated the absence of SIV p27 Ag in immature DC cultured alone and the lack of detectable viral levels in immature DC/unstimulated CD4+ T cell co-cultures until cells had been in culture for more than 7 days. FIV capsid protein was also undetected in feline bone-marrow-derived DC and DC/unstimulated PBMC co-cultures infected with FIV and cultured for 6 days (van der Meer et al., 2007). The low viral DNA levels in the DC/unstimulated CD4+ T cell co-cultures could reflect a lack of viral DNA integration into genomic DNA (Stevenson et al., 1990) and/or a block in reverse transcription, phenomena demonstrated in HIV-1 infection of unstimulated CD4+ T cells (Zack et al., 1992). Blocks in reverse transcription could also be due to the presence of the enzymically active, low-molecular-mass cytidine deaminase, APOBEC3G, which has been shown to inhibit HIV-1 infection in CD4+ T cells by an as yet undetermined cytidine-deaminase-independent mechanism (Chiu et al., 2005), and/or to the presence of Murr1, a gene product that has been shown to inhibit HIV-1 replication in unstimulated CD4+ T cells (Ganesh et al., 2003). It has also recently been shown that APOBEC3G inhibits HIV replication in immature DC through a cytidine-deaminase-dependent mechanism (Pion et al., 2006). In addition, upregulation of APOBEC3G in mature DC has been demonstrated, which could explain the comparatively decreased HIV replicative capacity in mature DC. FIV p26 capsid Ag was detected by 5 days after addition of activated CD4+ T cells to DC cultures. This result was as expected, since IL-2-stimulated cellular activation and proliferation have been shown to be necessary for productive HIV-1 infection (Zack et al., 1992; Oswald-Richter et al., 2004; Weissman et al., 1996).
The means by which DC transfer infection to T cells remains controversial. In order to test the possibilities that the transfer of FIV from feline DC to CD4+ T cells was by uptake of DC-replicated or endocytosed virus particles or by transfer of input virus bound to or endocytosed by DC, we recultured FIV-pulsed DC for 48 h before the addition of activated CD4+ T cells. FIV infection of CD4+ T cells remained unobstructed and productive infection ensued. While it is not known with certainty that the originally pulsed virus was completely degraded in the 48 h time period, de novo replication of FIV in these immature DC presents the most likely scenario for viral transfer to CD4+ T cells (Turville et al., 2004, 2005). This scenario is supported by an increase in FIV DNA and p26 capsid protein in FIV-pulsed DC after 9 days in culture compared with 0 or 2 days in culture. In addition, we attempted to block infection using the reverse transcriptase inhibitor, zidovudine (AZT); however, results were not interpretable due to toxicity of AZT, at antiviral concentrations, to DC. Our provisional conclusions are that immature feline DC transfer FIV infection to CD4+ T cells by immediate transfer of virus via exosomes and/or through endolysosomal pathways and that delayed transfer of virus occurs via de novo viral replication in DC, thus revealing observations parallel to those obtained with HIV-1 and immature human DC (Turville et al., 2004; Wiley & Gummuluru, 2006).
In summary, we have demonstrated that FIV can capitalize on initial DC/CD4+ T-cell interactions to transmit infection to amplifying CD4+ T cells, consistent with observations made with HIV-1 and SIV. While it may not be surprising that the interactions between immune deficiency viruses from different species and the innate immune system are similar, that these interactions are conserved illustrates the importance of understanding the mechanisms at work in this early stage of pathogenesis. That immunodeficiency-inducing lentiviruses are remarkably efficient in transferring infection to CD4+ T cells after DC capture reinforces a focus on mucosal vaccination and microbicide strategies to contain and/or prevent these infections.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Blom, J., Nielsen, C. & Rhodes, J. M. (1993). An ultrastructural study of HIV-infected human dendritic cells and monocytes/macrophages. APMIS 101, 672–680.[Medline]
Cameron, P. U., Freudenthal, P. S., Barker, J. M., Gezelter, S., Inaba, K. & Steinman, R. M. (1992). Dendritic cells exposed to human immunodeficiency virus type-1 transmit a vigorous cytopathic infection to CD4+ T cells. Science 257, 383–387.
Cameron, P. U., Lowe, M. G., Crowe, S. M., O'Doherty, U., Pope, M., Gezelter, S. & Steinman, R. M. (1994). Susceptibility of dendritic cells to HIV-1 infection in vitro. J Leukoc Biol 56, 257–265.[Abstract]
Chiu, Y. L., Soros, V. B., Kreisberg, J. F., Stopak, K., Yonemoto, W. & Greene, W. C. (2005). Cellular APOBEC3G restricts HIV-1 infection in resting CD4+ T cells. Nature 435, 108–114.[CrossRef][Medline]
Dreitz, M. J., Dow, S. W., Fiscus, S. A. & Hoover, E. A. (1995). Development of monoclonal antibodies and capture immunoassays for feline immunodeficiency virus. Am J Vet Res 56, 764–768.[Medline]
Frank, I. & Pope, M. (2002). The enigma of dendritic cell-immunodeficiency virus interplay. Curr Mol Med 2, 229–248.[CrossRef][Medline]
Frank, I., Piatak, M., Jr, Stoessel, H., Romani, N., Bonnyay, D., Lifson, J. D. & Pope, M. (2002). Infectious and whole inactivated simian immunodeficiency viruses interact similarly with primate dendritic cells (DCs): differential intracellular fate of virions in mature and immature DCs. J Virol 76, 2936–2951.
Frankel, S. S., Wenig, B. M., Burke, A. P., Mannan, P., Thompson, L. D., Abbondanzo, S. L., Nelson, A. M., Pope, M. & Steinman, R. M. (1996). Replication of HIV-1 in dendritic cell-derived syncytia at the mucosal surface of the adenoid. Science 272, 115–117.[Abstract]
Frankel, S. S., Tenner-Racz, K., Racz, P., Wenig, B. M., Hansen, C. H., Heffner, D., Nelson, A. M., Pope, M. & Steinman, R. M. (1997). Active replication of HIV-1 at the lymphoepithelial surface of the tonsil. Am J Pathol 151, 89–96.[Abstract]
Ganesh, L., Burstein, E., Guha-Niyogi, A., Louder, M. K., Mascola, J. R., Klomp, L. W., Wijmenga, C., Duckett, C. S. & Nabel, G. J. (2003). The gene product Murr1 restricts HIV-1 replication in resting CD4+ lymphocytes. Nature 426, 853–857.[CrossRef][Medline]
Granelli-Piperno, A., Delgado, E., Finkel, V., Paxton, W. & Steinman, R. M. (1998). Immature dendritic cells selectively replicate macrophagetropic (M-tropic) human immunodeficiency virus type 1, while mature cells efficiently transmit both M- and T-tropic virus to T cells. J Virol 72, 2733–2737.
Hu, J., Gardner, M. B. & Miller, C. J. (2000). Simian immunodeficiency virus rapidly penetrates the cervicovaginal mucosa after intravaginal inoculation and infects intraepithelial dendritic cells. J Virol 74, 6087–6095.
Ignatius, R., Isdell, F., O'Doherty, U. & Pope, M. (1998). Dendritic cells from skin and blood of macaques both promote SIV replication with T cells from different anatomical sites. J Med Primatol 27, 121–128.[Medline]
Leong, A. S. & Sormunen, R. T. (1998). Microwave procedures for electron microscopy and resin-embedded sections. Micron 29, 397–409.[CrossRef][Medline]
Lore, K., Smed-Sorensen, A., Vasudevan, J., Mascola, J. R. & Koup, R. A. (2005). Myeloid and plasmacytoid dendritic cells transfer HIV-1 preferentially to antigen-specific CD4+ T cells. J Exp Med 201, 2023–2033.
McDonald, D., Wu, L., Bohks, S. M., KewalRamani, V. N., Unutmaz, D. & Hope, T. J. (2003). Recruitment of HIV and its receptors to dendritic cell-T cell junctions. Science 300, 1295–1297.
Messmer, D., Ignatius, R., Santisteban, C., Steinman, R. M. & Pope, M. (2000). The decreased replicative capacity of simian immunodeficiency virus SIVmac239
nef is manifest in cultures of immature dendritic cells and T cells. J Virol 74, 2406–2413.
Milush, J. M., Kosub, D., Marthas, M., Schmidt, K., Scott, F., Wozniakowski, A., Brown, C., Westmoreland, S. & Sodora, D. L. (2004). Rapid dissemination of SIV following oral inoculation. AIDS 18, 2371–2380.[Medline]
Oswald-Richter, K., Grill, S. M., Leelawong, M. & Unutmaz, D. (2004). HIV infection of primary human T cells is determined by tunable thresholds of T cell activation. Eur J Immunol 34, 1705–1714.[CrossRef][Medline]
Patterson, S. & Knight, S. C. (1987). Susceptibility of human peripheral blood dendritic cells to infection by human immunodeficiency virus. J Gen Virol 68, 1177–1181.
Pedersen, N. C., Leutenegger, C. M., Woo, J. & Higgins, J. (2001). Virulence differences between two field isolates of feline immunodeficiency virus (FIV-A Petaluma and FIV-C PGammar) in young adult specific pathogen free cats. Vet Immunol Immunopathol 79, 53–67.[CrossRef][Medline]
Pion, M., Granelli-Piperno, A., Mangeat, B., Stalder, R., Correa, R., Steinman, R. M. & Piguet, V. (2006). APOBEC3G/3F mediates intrinsic resistance of monocyte-derived dendritic cells to HIV-1 infection. J Exp Med 203, 2887–2893.
Pope, M., Betjes, M. G., Romani, N., Hirmand, H., Cameron, P. U., Hoffman, L., Gezelter, S., Schuler, G. & Steinman, R. M. (1994). Conjugates of dendritic cells and memory T lymphocytes from skin facilitate productive infection with HIV-1. Cell 78, 389–398.[CrossRef][Medline]
Pope, M., Gezelter, S., Gallo, N., Hoffman, L. & Steinman, R. M. (1995). Low levels of HIV-1 infection in cutaneous dendritic cells promote extensive viral replication upon binding to memory CD4+ T cells. J Exp Med 182, 2045–2056.
Pope, M., Elmore, D., Ho, D. & Marx, P. (1997). Dendritic cell-T cell mixtures, isolated from the skin and mucosae of macaques, support the replication of SIV. AIDS Res Hum Retroviruses 13, 819–827.[Medline]
Sodora, D. L., Shpaer, E. G., Kitchell, B. E., Dow, S. W., Hoover, E. A. & Mullins, J. I. (1994). Identification of three feline immunodeficiency virus (FIV) env gene subtypes and comparison of the FIV and human immunodeficiency virus type 1 evolutionary patterns. J Virol 68, 2230–2238.
Sprague, W. S., Pope, M. & Hoover, E. A. (2005). Culture and comparison of feline myeloid dendritic cells vs macrophages. J Comp Pathol 133, 136–145.[CrossRef][Medline]
Stahl-Hennig, C., Steinman, R. M., Tenner-Racz, K., Pope, M., Stolte, N., Matz-Rensing, K., Grobschupff, G., Raschdorff, B., Hunsmann, G. & Racz, P. (1999). Rapid infection of oral mucosal-associated lymphoid tissue with simian immunodeficiency virus. Science 285, 1261–1265.
Stevenson, M., Stanwick, T. L., Dempsey, M. P. & Lamonica, C. A. (1990). HIV-1 replication is controlled at the level of T cell activation and proviral integration. EMBO J 9, 1551–1560.[Medline]
Turville, S. G., Santos, J. J., Frank, I., Cameron, P. U., Wilkinson, J., Miranda-Saksena, M., Dable, J., Stossel, H., Romani, N. & other authors (2004). Immunodeficiency virus uptake, turnover, and 2-phase transfer in human dendritic cells. Blood 103, 2170–2179.
Turville, S. G., Vermeire, K., Balzarini, J. & Schols, D. (2005). Sugar-binding proteins potently inhibit dendritic cell human immunodeficiency virus type 1 (HIV-1) infection and dendritic-cell-directed HIV-1 transfer. J Virol 79, 13519–13527.
Unutmaz, D., KewalRamani, V. N., Marmon, S. & Littman, D. R. (1999). Cytokine signals are sufficient for HIV-1 infection of resting human T lymphocytes. J Exp Med 189, 1735–1746.
van der Meer, F. J., Schuurman, N. M. & Egberink, H. F. (2007). Feline immunodeficiency virus infection is enhanced by feline bone marrow-derived dendritic cells. J Gen Virol 88, 251–258.
Weissman, D., Daucher, J., Barker, T., Adelsberger, J., Baseler, M. & Fauci, A. S. (1996). Cytokine regulation of HIV replication induced by dendritic cell–CD4-positive T cell interactions. AIDS Res Hum Retroviruses 12, 759–767.[Medline]
Wiley, R. D. & Gummuluru, S. (2006). Immature dendritic cell-derived exosomes can mediate HIV-1 trans infection. Proc Natl Acad Sci U S A 103, 738–743.
Zack, J. A., Haislip, A. M., Krogstad, P. & Chen, I. S. (1992). Incompletely reverse-transcribed human immunodeficiency virus type 1 genomes in quiescent cells can function as intermediates in the retroviral life cycle. J Virol 66, 1717–1725.
Zhang, Z., Schuler, T., Zupancic, M., Wietgrefe, S., Staskus, K. A., Reimann, K. A., Reinhart, T. A., Rogan, M., Cavert, W. & other authors (1999). Sexual transmission and propagation of SIV and HIV in resting and activated CD4+ T cells. Science 286, 1353–1357.
Received 6 April 2007;
accepted 17 November 2007.
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), with unstimulated CD4+ T cells (
) or with activated CD4+ T cells (
) for 7 days at 37 °C. Data are presented as the means±SD compiled from at least seven experiments using at least five different animals. *, Denote significant differences between DC and DC+T cells versus DC+T blasts.
