This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Münch, J. Articles by Kirchhoff, F. Search for Related Content PubMed PubMed Citation Articles by Münch, J. Articles by Kirchhoff, F.

 Previous Article  |  Next Article 

Journal of Virology, November 2001, p. 10532-10536, Vol. 75, No. 21
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.21.10532-10536.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Efficient Class I Major Histocompatibility Complex Down-Regulation by Simian Immunodeficiency Virus Nef Is Associated with a Strong Selective Advantage in Infected Rhesus Macaques

Jan Münch,^1, Nicole Stolte,² Dietmar Fuchs,³ Christiane Stahl-Hennig,² and Frank Kirchhoff^1,*

Institute for Clinical and Molecular Virology, University of Erlangen-Nürnberg, 91054 Erlangen,¹ and German Primate Center, 37077 Göttingen,² Germany, and Institute of Medicinal Chemistry and Biochemistry, University of Innsbruck and Ludwig Bolzmann Institute of AIDS Research, A-6020 Innsbruck, Austria³

Received 16 May 2001/Accepted 30 July 2001

	ABSTRACT

Top Abstract Text References

Substitution of Y223F disrupts the ability of simian immunodeficiency virus (SIV) Nef to down-modulate major histocompatibility complex (MHC) class I from the cell surface but has no effect on other Nef functions, such as down-regulation of CD4, CD28, and CD3 cell surface expression or stimulation of viral replication and enhancement of virion infectivity. Inoculation of three rhesus macaques with the SIVmac239 Y223F-Nef variant revealed that this point mutation consistently reverts and that Nef activity in MHC class I down-modulation is fully restored within 4 weeks after infection. Our results demonstrate a strong selective pressure for a tyrosine at amino acid position 223 in SIV Nef, and they constitute evidence that Nef-mediated MHC class I down-regulation provides a selective advantage for viral replication in vivo.

	TEXT

Top Abstract Text References

The Nef protein is a regulatory factor of human and simian immunodeficiency viruses (HIV and SIV, respectively) that is important for efficient viral replication and persistence in vivo (11, 20, 21). Several in vitro activities of HIV and SIV Nef which may be relevant for viral pathogenicity have been described. Nef down-regulates cell surface expression of CD4 (1, 4, 14, 38), CD28 (39), and major histocompatibility complex class I (MHC-I) molecules (25, 26, 34). It also alters the normal function of the T-cell-receptor (TCR)-CD3 signaling complex in T lymphocytes and modulates cellular activation pathways (3, 5, 18, 33, 35). Furthermore, Nef induces Fas ligand expression and might promote the killing of bystander cells (15, 41). Finally, Nef increases the infectivity of viral particles and enhances viral replication in primary lymphocytes and in human lymphoid tissue ex vivo (8, 12, 16, 24, 30, 36). Recent findings suggest that several conserved in vitro functions of Nef are independently selected in HIV type 1 (HIV-1)-infected individuals and contribute to AIDS pathogenesis (7). However, the exact role of Nef in AIDS pathogenesis still remains unclear.

Several lines of evidence suggest that MHC-I down-regulation might contribute to efficient viral replication and disease induction in vivo. Both HIV-1 and SIV proteins down-regulate steady-state expression of MHC-I complexes assembled with A and B, but not C, heavy chains from the surfaces of T lymphocytes and macrophages (9, 26). Selective down-regulation of HLA-A and HLA-B antigens protects HIV-infected cells from killing by cytotoxic T cells and by natural killer cells in vitro (9, 10). Such protection likely helps HIV-1 to evade the host immune response in vivo (for reviews, see references 13 and 31). Recently, it has been demonstrated that only nef alleles obtained during the asymptomatic phase of HIV-1 infection efficiently down-modulate MHC-I (7). Thus, a selective pressure for this particular Nef function apparently exists only in immunocompetent hosts.

These results are highly suggestive. However, the physiological relevance of MHC-I down-regulation has been called into question, particularly since this effect requires relatively high Nef expression levels (25, 26, 34). To date no direct evidence that MHC-I down-regulation contributes to viral spread in vivo has been provided. To address this point, we analyzed a Nef variant of the pathogenic SIVmac239 clone, containing a Y223F substitution in the unique C-terminal region of Nef (38), both in vitro and in vivo in rhesus macaques. Flow cytometry analysis of Jurkat T cells, transfected with a bicistronic vector coexpressing Nef and green fluorescent protein (GFP) (28), confirmed previous reports (38, 39), showing that this alteration disrupts MHC-I down-regulation but does not affect down-regulation of cell surface expression of CD4, CD28, and CD3 molecules (Fig. 1). Furthermore, the Y223F-Nef increased SIV infectivity and replication, with an efficiency undistinguishable from that of 239wt Nef (reference 38 and data not shown). Thus, the Y223F substitution in SIV Nef selectively disrupts MHC-I down-regulation.

View larger version (89K): [in this window] [in a new window]   FIG. 1.   Substitution of Y223F in 239-Nef selectively disrupts down-regulation of MHC-I. Jurkat T cells were transiently transfected with a control vector expressing GFP alone or with plasmids coexpressing GFP and the truncated 239nef*, 239wt, or 239Y223F nef genes. CD4, MHC-I, CD28, and CD3 expression was analyzed by two-color flow cytometry.

Three juvenile rhesus macaques, Mm10029, Mm10030, and Mm10031, were infected by intravenous inoculation of SIVmac239 Y223F-Nef, containing 5 ng of p27 produced by transfected 293T cells. The animals were healthy and seronegative for SIV, D-type retroviruses, and simian T-lymphotropic virus type 1 at the time of infection. Sera and cells were collected at regular intervals, and serological, virological, and immunological analyses of all samples were performed as described previously (6, 19, 24, 40). The same methods were used to quantitate viral replication in animals infected with the Y223F variant and in historical controls that received similar doses of virus. During acute infection, the levels of p27 gag antigenemia and of viral RNA in cell-free plasma for Mm10030 and Mm10031 were similar to those of some 239wt-infected animals (Fig. 2A and B). In the remaining animal, Mm10029, the amount of detectable p27 (226 pg/ml) was intermediate between SIVmac239wt (3,612 ± 2,741 pg/ml; n = 15) and NU infection (68 ± 45 pg/ml; n = 4) (Fig. 2A). Thus, the Y223F-Nef variant was capable of enhancing SIVmac replication during acute infection.

View larger version (23K): [in this window] [in a new window]   FIG. 2.   Replication of the SIVmac239 Y223F variant in acutely infected rhesus macaques. (A) Peak levels of p27 plasma antigenemia observed at 2 weeks p.i. For comparison, values obtained from four macaques infected with NU and from 15 animals infected with 239wt are indicated. (B) Viral RNA load. The detection limit for viral RNA is approximately 40 copies/ml (40). (C) Number of infectious cells per 1 million PBMC. For comparison, average values obtained from rhesus macaques infected with SIVmac239 NU () or wild-type SIVmac239 () are shown in panels B and C.

The three macaques that received the Y223F-Nef variant became chronically infected and survived the 1st year of infection. In contrast, about 60 to 70% of 239wt-infected animals die of AIDS within this period (20). Cell-associated viral loads were comparable or only slightly reduced compared to 239wt infection in Mm10029 and Mm10030 (Fig. 2C). Mm10031 showed about 100-fold-reduced frequencies of infectious peripheral blood mononuclear cells (PBMC) by week 20 after infection and very low levels of viral plasma RNA (Fig. 2B and C). The SIVmac239 Y223F-Nef-infected animals remained clinically healthy throughout the 56-week observation period. All three animals exhibited transient anemia to varying degrees from week 4 to 8 postinfection (p.i.). However, blood counts recovered thereafter. Mm10030 developed a moderate persistent lymphadenopathy by week 4 after infection. In Mm10030 and Mm10031 the percentage of CD4⁺ T cells declined slowly during the investigation period (Fig. 3A). Mm10029 also showed declining CD4⁺ lymphocyte counts until 28 weeks p.i., followed by partial recovery. The percentage of CD4⁺ CD29⁺ memory T cells decreased transiently at 2 weeks p.i. (Fig. 3B), when maximum levels of viral replication were observed (Fig. 2). Overall, the characteristics of infection with the Y223F-Nef variant were more similar to those of 239wt than nef-deleted infection. However, it is remarkable that the three macaques that received the Y223F variant are clinically healthy at 56 weeks p.i., whereas the majority of 239wt-infected macaques develop simian AIDS and die within the 1st year. Our results suggest that the Y223F variant might be more effectively controlled by the antiviral immune response than 239wt.

View larger version (22K): [in this window] [in a new window]   FIG. 3.   CD4+ T-cell counts in macaques infected with the SIVmac239 Y223F-Nef variant. Shown are percentages of total CD4+ T cells (A) and of CD4+CD29+ memory T cells (B) in peripheral blood of the three animals inoculated with the SIVmac239 Y223F-Nef variant.

Point mutations in nef that disrupt important functions revert rapidly in infected animals (6, 20). Therefore, we analyzed the stability of the Y223F substitution in vivo. As shown in Fig. 4, Nef activity in MHC-I down-regulation was efficiently restored by 4 weeks p.i. Next, we investigated whether the phenotypic reversions correlated with the selection of revertants. SIV sequences spanning the entire nef gene were amplified from recombinant PBMC DNA or from viral plasma RNA as described previously (19, 24). Sequence analysis revealed that most nef alleles obtained after the acute phase of infection predicted reversion of Y223FY (data not shown). Reversions were consistently observed in all three animals, and forms containing a tyrosine at position 223 in Nef predominated throughout the course of infection.

View larger version (48K): [in this window] [in a new window]   FIG. 4.   Phenotypic reversions of the Y223F-Nef mutant in vivo. Viral RNA was isolated from plasma obtained from Mm10029 at the indicated number of weeks p.i. (wpi), reverse transcribed, and subjected to nested PCR. Amplified PCR fragments were cloned as a pool into a vector coexpressing Nef and GFP from a single bicistronic RNA. Subsequently, the effects of these nef alleles on CD4 and MHC-I expression were determined as described in Materials and Methods. Similar results were obtained with plasma samples obtained from Mm10030 and Mm10031.

Our results demonstrate that a point mutation of Y223F in SIVmac239 Nef reverts efficiently in infected macaques. The Y223F change selectively disrupts MHC-I down-regulation, having no detectable effect on functional Nef activity in down-modulation of CD3, CD28, and CD4 cell surface expression. Furthermore, it did not reduce the ability of Nef to increase the infectivity of viral particles or to stimulate SIV replication in PBMC or in 221 cells. Therefore, our results are evidence that Nef-mediated MHC-I down-regulation is associated with a selective advantage for SIVmac replication in vivo. Our findings are in agreement with those of a recent study suggesting an important role of the C-terminal domain of SIVmac Nef in viral pathogenesis (23).

Mutation of Y223F consistently reverted between 2 and 4 weeks after infection. The efficiency of reversion indicates a strong selective pressure for a tyrosine at position 223 in SIV Nef. However, stop codons in Nef usually revert even faster, within 1 to 2 weeks p.i. (20). The slightly delayed selection of revertants might be explained by the fact that the specific nucleotide change required to restore Y223 simply takes more time to occur than the changes required for reversion of a premature stop codon. However, we have previously observed that even three point mutations in Nef can revert within 2 weeks p.i. (6). Notably, in SIV-infected macaques the virus-specific cytotoxic T-lymphocyte (CTL) response usually peaks after about 2 weeks (22). Thus, the efficient selection of revertants between weeks 2 and 4 p.i. likely reflects the selective pressure to restore the ability of Nef to down-regulate MHC-I due to an efficient antiviral CTL response.

The Y223F mutation that disrupted MHC-I down-regulation predominated only very early after infection. The forms that evolved thereafter expressed wild-type Nef and replicated relatively efficiently compared to SIV with nef deleted. Notably, however, all three animals showed a nonprogressor or slow-progressor phenotype. These findings suggest that the inability of the virus to down-modulate MHC-I during the acute phase of infection might have long-term beneficial effects on the clinical outcome of infection. It has been shown that the levels of HIV-1 replication during acute infection are an important prognostic marker for disease progression and that long-lasting effects can be obtained by short-term antiviral therapy during primary HIV-1 and SIV infection (27, 32, 37). Down-regulation of MHC-I by Nef likely protects infected T cells from recognition and destruction by the host immune system (10). The Y223F mutation should enhance viral propagation and provide a selective advantage for SIV replication only after the onset of the antiviral immune response. It was beyond the scope of this study to quantitate the CTL responses in both Y223F-Nef- and 239wt-infected animals. It is conceivable, however, that impaired MHC-I down-regulation early after infection results in enhanced presentation of viral antigens and enables the infected host to mount stronger CTL responses, resulting in more-efficient immune control than in 239wt infected-macaques.

SIV and HIV-1 Nef proteins use different surfaces to down-regulate MHC-I cell surface expression (2, 17, 25, 29, 38). Therefore, our results with the SIV macaque model cannot be directly applied to HIV-1-infected humans. Nonetheless, we believe that MHC-I down-regulation likely plays a similar role in efficient viral persistence of both HIV-1 and SIVmac infection. First, both HIV-1 and SIV Nef proteins use a similar mechanism to down-regulate MHC-I expression, which requires the conserved tyrosine residue Y320 in class I heavy chains and involves the accelerated endocytosis of the MHC-I complex from the cell surface (38). Second, we have recently demonstrated that nef alleles obtained from asymptomatic HIV-1-infected individuals, but not those derived from AIDS patients, effectively down-modulate MHC-I (7). Concordant with the results of the present study, these findings strongly suggest that MHC-I down-regulation by both SIV and HIV-1 Nef contributes to viral spread in vivo.

Much remains to be done to fully elucidate the relative contributions of the different in vitro Nef activities to viral pathogenesis. However, accumulating evidence suggests that multiple Nef functions, including CD4 down-regulation, contribute to efficient replication in vivo (7, 19). Furthermore, independent Nef functions are modulated during disease progression to optimize viral spread at different clinical stages of HIV-1 infection (7). Thus, HIV-1 and SIV have evolved complex mechanisms for efficient viral persistence in vivo. We utilized the Y223F mutation because it was highly selective for MHC-I down-regulation and because a single homologous substitution minimizes the risk that additional Nef functions or interactions are affected. While this possibility cannot be entirely dismissed, it is highly likely that the reversion of the Y223F substitution indeed reflects a selective pressure for Nef-mediated MHC-I down-regulation in vivo. However, because of the efficient and rapid selection of revertant viruses, our study does not provide information on the consequences of inefficient class I down-modulation for viral persistence and disease progression. Therefore, studies with SIVmac239 mutants containing difficult-to-revert deletions in the C-terminal domain of Nef are required to further clarify the importance of MHC-I down-regulation for SIV replication and AIDS pathogenesis in infected rhesus macaques.

	ACKNOWLEDGMENTS

We thank Mandy Krumbiegel and Nathaly Finze for excellent technical assistance; Ronald C. Desrosiers, Jacek Skowronski, and John Iafrate for helpful discussions and for sharing unpublished results; and Ingrid Bennett for critical reading of the manuscript. We also thank Bernhard Fleckenstein for constant support and encouragement and Peter Ten Haaft and Jonathan L. Heeney for quantitation of viral RNA loads.

This work was supported by the Wilhelm-Sander Foundation, BMBF grant 01Ki9478, and the Deutsche Forschungsgemeinschaft.

	FOOTNOTES

^* Corresponding author. Present address: Abteilung VirologieUniversitätsklinikum, Albert-Einstein-Allee 11, 89081 Ulm, Germany. Phone: 49-731-50023344. Fax: 49-731-50023337. E-mail: frank.kirchhoff{at}medizin.uni-ulm.de.

Present address: Abteilung VirologieUniversitätsklinikum, 89081 Ulm, Germany.

	REFERENCES

Top Abstract Text References

1.	Aiken, C., J. Konner, N. R. Landau, M. E. Lenburg, and D. Trono. 1994. Nef induces CD4 endocytosis: requirement for a critical dileucine motif in the membrane-proximal CD4 cytoplasmic domain. Cell 76:853-864[CrossRef][Medline].
2.	Akari, H., S. Arold, T. Fukumori, T. Okazaki, K. Strebel, and A. Adachi. 2000. Nef-induced major histocompatibility complex class I down-regulation is functionally dissociated from its virion incorporation, enhancement of viral infectivity, and CD4 down-regulation. J. Virol. 74:2907-2912[Abstract/Free Full Text].
3.	Alexander, L., Z. Du, M. Rosenzweig, J. U. Jung, and R. C. Desrosiers. 1997. A role for natural simian immunodeficiency virus and human immunodeficiency virus type 1 nef alleles in lymphocyte activation. J. Virol. 71:6094-6099[Abstract].
4.	Anderson, S., D. C. Shugars, R. Swanstrom, and J. V. Garcia. 1993. Nef from primary isolates of human immunodeficiency virus type 1 suppresses surface CD4 expression in human and mouse T cells. J. Virol. 67:4923-4931[Abstract/Free Full Text].
5.	Bell, I., C. Ashman, J. Maughan, E. Hooker, F. Cook, and T. A. Reinhart. 1998. Association of simian immunodeficiency virus Nef with the T-cell receptor (TCR)  chain leads to TCR down-modulation. J. Gen. Virol. 79:2717-2727[Abstract].
6.	Carl, S., A. J. Iafrate, S. M. Lang, C. Stahl-Hennig, E. M. Kuhn, D. Fuchs, K. Mätz-Rensing, P. ten Haaft, J. L. Heeney, J. Skowronski, and F. Kirchhoff. 1999. The acidic region and conserved putative protein kinase C phosphorylation site in Nef are important for SIV replication in rhesus macaques. Virology 257:138-155[CrossRef][Medline].
7.	Carl, S., T. C. Greenough, M. Krumbiegel, M. Greenberg, J. Skowronski, J. L. Sullivan, and F. Kirchhoff. 2001. Modulation of different human immunodeficiency virus type 1 Nef functions during progression to AIDS. J. Virol. 75:3657-3665[Abstract/Free Full Text].
8.	Chowers, M. Y., C. A. Spina, T. J. Kwoh, N. J. Fitch, D. D. Richman, and J. C. Guatelli. 1994. Optimal infectivity in vitro of human immunodeficiency virus type 1 requires an intact nef gene. J. Virol. 68:2906-2914[Abstract/Free Full Text].
9.	Cohen, G. B., R. T. Gandhi, D. M. Davis, O. Mandelboim, B. K. Chen, J. L. Strominger, and D. Baltimore. 1999. The selective dowregulation of class I major histocompatibility complex proteins by HIV-1 protects HIV-infected cells from NK cells. Immunity 10:661-671[CrossRef][Medline].
10.	Collins, K. L., B. K. Chen, S. A. Kalams, B. D. Walker, and D. Baltimore. 1998. HIV-1 Nef protein protects infected primary cells against killing by cytotoxic T lymphocytes. Nature 391:397-401[CrossRef][Medline].
11.	Deacon, N. J., A. Tsykin, A. Solomon, K. Smith, M. Ludford-Menting, D. J. Hooker, D. A. McPhee, A. L. Greenway, A. Ellett, and C. Chatfield. 1995. Genomic structure of an attenuated quasispecies of HIV-1 from a blood transfusion donor and recipients. Science 270:988-991[Abstract/Free Full Text].
12.	deRonde, A., B. Klaver, W. Keulen, L. Smit, and J. Goudsmit. 1992. Natural HIV-1 NEF accelerates virus replication in primary human lymphocytes. Virology 188:391-395[CrossRef][Medline].
13.	Desrosiers, R. C. 1999. Strategies used by human immunodeficiency virus that allow persistent viral replication. Nat. Med. 5:723-725[CrossRef][Medline].
14.	Garcia, J. V., and A. D. Miller. 1991. Serine phosphorylation-independent down-regulation of cell-surface CD4 by nef. Nature 350:508-511[CrossRef][Medline].
15.	Geleziunas, R., W. Xu, K. Takeda, H. Ichijo, and W. C. Greene. 2001. HIV-1 Nef inhibits ASK1-dependent death signalling, providing a potential mechanism for protecting the infected host cell. Nature 410:834-838[CrossRef][Medline].
16.	Glushakova, S., J. C. Grivel, K. Suryanarayana, P. Meylan, J. D. Lifson, R. C. Desrosiers, and L. Margolis. 1999. Nef enhances human immunodeficiency virus replication and responsiveness to interleukin-2 in human lymphoid tissue ex vivo. J. Virol. 73:3968-3974[Abstract/Free Full Text].
17.	Greenberg, M. E., A. J. Iafrate, and J. Skowronski. 1998. The SH3 domain-binding surface and an acidic motif in HIV-1 Nef regulate trafficking of class I MHC complexes. EMBO J. 17:2777-2789[CrossRef][Medline].
18.	Iafrate, A. J., S. Bronson, and J. Skowronski. 1997. Separable functions of Nef disrupt two aspects of T cell receptor machinery: CD4 expression and CD3 signaling. EMBO J. 16:673-684[CrossRef][Medline].
19.	Iafrate, A. J., S. Carl, S. Bronson, C. Stahl-Hennig, T. Swigut, J. Skowronski, and F. Kirchhoff. 2000. Disrupting surfaces of Nef required for down-regulation of CD4 and for enhancement of virion infectivity attenuates simian immunodeficiency virus replication in vivo. J. Virol. 74:9836-9844[Abstract/Free Full Text].
20.	Kestler, H. W., D. J. Ringler, K. Mori, D. L. Panicali, P. K. Sehgal, M. D. Daniel, and R. C. Desrosiers. 1991. Importance of the nef gene for maintenance of high virus loads and for development of AIDS. Cell 65:651-662[CrossRef][Medline].
21.	Kirchhoff, F., T. C. Greenough, D. B. Brettler, J. L. Sullivan, and R. C. Desrosiers. 1995. Absence of intact nef sequences in a long-term, nonprogressing survivor of HIV-1 infection. N. Engl. J. Med. 332:228-232[Free Full Text].
22.	Kuroda, M. J., J. E. Schmitz, W. A. Charini, C. E. Nickerson, M. A. Lifton, C. I. Lord, M. A. Forman, and N. L. Letvin. 1999. Emergence of CTL coincides with clearance of virus during primary simian immunodeficiency virus infection in rhesus monkeys. J. Immunol. 162:5127-5133[Abstract/Free Full Text].
23.	Lafont, B. A., Y. Riviere, L. Gloecker, C. Beyer, B. Hurtrel, M. P. Kieny, A. Kirn, and A. M. Aubertin. 2000. Implication of the C-terminal domain of Nef in the reversion to pathogenicity of attenuated SIV macBK28-41 in macaques. Virology 266:286-298[CrossRef][Medline].
24.	Lang, S. M., A. J. Iafrate, C. Stahl-Hennig, E. M. Kuhn, T. Nißlein, M. Haupt, G. Hunsmann, J. Skowronski, and F. Kirchhoff. 1997. Association of simian immunodeficiency virus Nef with cellular serine/threonine kinases is dispensable for the development of AIDS in rhesus macaques. Nat. Med. 3:860-865[CrossRef][Medline].
25.	Le Gall, S., M. C. Prevost, J. M. Heard, and O. Schwartz. 1997. Human immunodeficiency virus type 1 Nef independently affects virion incorporation of major histocompatibility complex class I molecules and virus infectivity. Virology 229:295-301[CrossRef][Medline].
26.	Le Gall, S., L. Erdtmann, S. Benichou, C. Berlioz-Torrent, L. Liu, R. Benarous, J. M. Heard, and O. Schwarz. 1998. Nef interacts with the mu subunit of clathrin adapter complexes and reveals a cryptic sorting signal in MHC-I molecules. Immunity 8:483-495[CrossRef][Medline].
27.	Lisziewicz, J., E. Rosenberg, J. Lieberman, H. Jessen, L. Lopalco, R. Siliciano, B. Walker, and F. Lori. 1999. HIV control following discontinuation of antiretroviral therapy. N. Engl. J. Med. 340:1683-1684[Free Full Text].
28.	Lock, M., M. E. Greenberg, A. J. Iafrate, T. Swigut, J. Münch, F. Kirchhoff, N. Shohdy, and J. Skowronski. 1999. Two elements target SIV Nef to the AP-2 clathrin adaptor complex, but only one is required for the induction of CD4 endocytosis. EMBO J. 18:2722-2733[CrossRef][Medline].
29.	Mangasarian, A., V. Piguet, J. K. Wang, Y. L. Chen, and D. Trono. 1999. Nef-induced CD4 and major histocompatibility complex class I (MHC-I) down-regulation are governed by distinct determinants: N-terminal  helix and proline repeat of Nef selectively regulate MHC-I trafficking. J. Virol. 73:1964-1973[Abstract/Free Full Text].
30.	Miller, M. D., M. T. Warmerdam, I. Gaston, W. C. Greene, and M. B. Feinberg. 1994. The human immunodeficiency virus-1 nef gene product: a positive factor for viral infection and replication in primary lymphocytes and macrophages. J. Exp. Med. 179:101-114[Abstract/Free Full Text].
31.	Ploegh, H. L. 1998. Viral strategies of immune evasion. Science 280:248-253[Abstract/Free Full Text].
32.	Rosenwirth, B., P. ten Haaft, W. M. J. M. Bogers, I. G. Nieuwenhuis, H. Niphuis, E.-M. Kuhn, N. Bischofberger, J. L. Heeney, and K. Überla. 2000. Antiretroviral therapy during primary immunodeficiency virus infection can induce persistent suppression of virus load and protection from heterologous challenge in rhesus macaques. J. Virol. 74:1704-1711[Abstract/Free Full Text].
33.	Schrager, J. A., and J. W. Marsh. 1999. HIV-1 Nef increases T cell activation in a stimulus-dependent manner. Proc. Natl. Acad. Sci. USA 96:8167-8172[Abstract/Free Full Text].
34.	Schwartz, O., V. Marechal, S. Le Gall, F. Lemonnier, and J. M. Heard. 1996. Endocytosis of major histocompatibility complex class I molecules is induced by the HIV-1 Nef protein. Nat. Med. 2:338-342[CrossRef][Medline].
35.	Skowronski, J., D. Parks, and R. Mariani. 1993. Altered T cell activation and development in transgenic mice expressing the HIV-1 nef gene. EMBO J. 12:703-713[Medline].
36.	Spina, C. A., T. J. Kwoh, M. Y. Chowers, J. C. Guatelli, and D. D. Richman. 1994. The importance of nef in the induction of human immunodeficiency virus type 1 replication from primary quiescent CD4 lymphocytes. J. Exp. Med. 179:115-123[Abstract/Free Full Text].
37.	Spring, M., C. Stahl-Hennig, N. Stolte, N. Bischofberger, J. L. Heeney, P. ten Haaft, K. Tenner-Racz, P. Racz, D. Lorenzen, G. Hunsmann, and U. Dittmer. 2001. Enhanced cellular immune response and reduced CD8+ lymphocyte apoptosis in acutely SIV-infected rhesus macaques after short-term antiretroviral treatment. Virology 279:221-232[CrossRef][Medline].
38.	Swigut, T., A. J. Iafrate, J. Münch, F. Kirchhoff, and J. Skowronski. 2000. Simian and human immunodeficiency virus Nef proteins use different surfaces to down-regulate class I major histocompatibility antigen expression. J. Virol. 74:5691-5701[Abstract/Free Full Text].
39.	Swigut, T., N. Shody, and J. Skowronski. 2001. Mechanism for down-regulation of CD28 by Nef. EMBO J. 20:1593-1604[CrossRef][Medline].
40.	ten Haaft, P., B. Verstrepen, K. Überla, B. Rosenwirth, and J. Heeney. 1998. A pathogenic threshold of virus load defined in simian immunodeficiency virus- or simian-human immunodeficiency virus-infected macaques. J. Virol. 72:10281-10285[Abstract/Free Full Text].
41.	Xu, X. N., B. Laffert, G. R. Screaton, M. Kraft, D. Wolf, W. Kolanus, J. Mongkolsapay, A. J. McMichael, and A. S. Baur. 1999. Induction of Fas ligand expression by HIV involves the interaction of Nef with the T cell receptor  chain. J. Exp. Med. 189:1489-1496[Abstract/Free Full Text].

This article has been cited by other articles:

• DeGottardi, M. Q., Specht, A., Metcalf, B., Kaur, A., Kirchhoff, F., Evans, D. T. (2008). Selective Downregulation of Rhesus Macaque and Sooty Mangabey Major Histocompatibility Complex Class I Molecules by Nef Alleles of Simian Immunodeficiency Virus and Human Immunodeficiency Virus Type 2. J. Virol. 82: 3139-3146 [Abstract] [Full Text]  
• Munch, J., Rajan, D., Schindler, M., Specht, A., Rucker, E., Novembre, F. J., Nerrienet, E., Muller-Trutwin, M. C., Peeters, M., Hahn, B. H., Kirchhoff, F. (2007). Nef-Mediated Enhancement of Virion Infectivity and Stimulation of Viral Replication Are Fundamental Properties of Primate Lentiviruses. J. Virol. 81: 13852-13864 [Abstract] [Full Text]  
• Schindler, M., Rajan, D., Specht, A., Ritter, C., Pulkkinen, K., Saksela, K., Kirchhoff, F. (2007). Association of Nef with p21-Activated Kinase 2 Is Dispensable for Efficient Human Immunodeficiency Virus Type 1 Replication and Cytopathicity in Ex Vivo-Infected Human Lymphoid Tissue. J. Virol. 81: 13005-13014 [Abstract] [Full Text]  
• Sacha, J. B., Chung, C., Reed, J., Jonas, A. K., Bean, A. T., Spencer, S. P., Lee, W., Vojnov, L., Rudersdorf, R., Friedrich, T. C., Wilson, N. A., Lifson, J. D., Watkins, D. I. (2007). Pol-Specific CD8+ T Cells Recognize Simian Immunodeficiency Virus-Infected Cells Prior to Nef-Mediated Major Histocompatibility Complex Class I Downregulation. J. Virol. 81: 11703-11712 [Abstract] [Full Text]  
• Roeth, J. F., Collins, K. L. (2006). Human Immunodeficiency Virus Type 1 Nef: Adapting to Intracellular Trafficking Pathways. Microbiol. Mol. Biol. Rev. 70: 548-563 [Abstract] [Full Text]  
• Brenner, M., Munch, J., Schindler, M., Wildum, S., Stolte, N., Stahl-Hennig, C., Fuchs, D., Matz-Rensing, K., Franz, M., Heeney, J., Ten Haaft, P., Swigut, T., Hrecka, K., Skowronski, J., Kirchhoff, F. (2006). Importance of the N-Distal AP-2 Binding Element in Nef for Simian Immunodeficiency Virus Replication and Pathogenicity in Rhesus Macaques. J. Virol. 80: 4469-4481 [Abstract] [Full Text]  
• Brown, A., Gartner, S., Kawano, T., Benoit, N., Cheng-Mayer, C. (2005). HLA-A2 down-regulation on primary human macrophages infected with an M-tropic EGFP-tagged HIV-1 reporter virus. J. Leukoc. Biol. 78: 675-685 [Abstract] [Full Text]  
• Munch, J., Schindler, M., Wildum, S., Rucker, E., Bailer, N., Knoop, V., Novembre, F. J., Kirchhoff, F. (2005). Primary Sooty Mangabey Simian Immunodeficiency Virus and Human Immunodeficiency Virus Type 2 nef Alleles Modulate Cell Surface Expression of Various Human Receptors and Enhance Viral Infectivity and Replication. J. Virol. 79: 10547-10560 [Abstract] [Full Text]  
• Schindler, M., Munch, J., Kirchhoff, F. (2005). Human Immunodeficiency Virus Type 1 Inhibits DNA Damage-Triggered Apoptosis by a Nef-Independent Mechanism. J. Virol. 79: 5489-5498 [Abstract] [Full Text]  
• Kasper, M. R., Roeth, J. F., Williams, M., Filzen, T. M., Fleis, R. I., Collins, K. L. (2005). HIV-1 Nef Disrupts Antigen Presentation Early in the Secretory Pathway. J. Biol. Chem. 280: 12840-12848 [Abstract] [Full Text]  
• Swigut, T., Alexander, L., Morgan, J., Lifson, J., Mansfield, K. G., Lang, S., Johnson, R. P., Skowronski, J., Desrosiers, R. (2004). Impact of Nef-Mediated Downregulation of Major Histocompatibility Complex Class I on Immune Response to Simian Immunodeficiency Virus. J. Virol. 78: 13335-13344 [Abstract] [Full Text]  
• Schindler, M., Munch, J., Brenner, M., Stahl-Hennig, C., Skowronski, J., Kirchhoff, F. (2004). Comprehensive Analysis of Nef Functions Selected in Simian Immunodeficiency Virus-Infected Macaques. J. Virol. 78: 10588-10597 [Abstract] [Full Text]  
• Kirchhoff, F., Schindler, M., Bailer, N., Renkema, G. H., Saksela, K., Knoop, V., Muller-Trutwin, M. C., Santiago, M. L., Bibollet-Ruche, F., Dittmar, M. T., Heeney, J. L., Hahn, B. H., Munch, J. (2004). Nef Proteins from Simian Immunodeficiency Virus-Infected Chimpanzees Interact with p21-Activated Kinase 2 and Modulate Cell Surface Expression of Various Human Receptors. J. Virol. 78: 6864-6874 [Abstract] [Full Text]  
• Lundquist, C. A., Zhou, J., Aiken, C. (2004). Nef Stimulates Human Immunodeficiency Virus Type 1 Replication in Primary T Cells by Enhancing Virion-Associated gp120 Levels: Coreceptor-Dependent Requirement for Nef in Viral Replication. J. Virol. 78: 6287-6296 [Abstract] [Full Text]  
• Stumptner-Cuvelette, P., Jouve, M., Helft, J., Dugast, M., Glouzman, A.-S., Jooss, K., Raposo, G., Benaroch, P. (2003). Human Immunodeficiency Virus-1 Nef Expression Induces Intracellular Accumulation of Multivesicular Bodies and Major Histocompatibility Complex Class II Complexes: Potential Role of Phosphatidylinositol 3-Kinase. Mol. Biol. Cell 14: 4857-4870 [Abstract] [Full Text]  
• Casartelli, N., Di Matteo, G., Potesta, M., Rossi, P., Doria, M. (2003). CD4 and Major Histocompatibility Complex Class I Downregulation by the Human Immunodeficiency Virus Type 1 Nef Protein in Pediatric AIDS Progression. J. Virol. 77: 11536-11545 [Abstract] [Full Text]  
• Schindler, M., Wurfl, S., Benaroch, P., Greenough, T. C., Daniels, R., Easterbrook, P., Brenner, M., Munch, J., Kirchhoff, F. (2003). Down-Modulation of Mature Major Histocompatibility Complex Class II and Up-Regulation of Invariant Chain Cell Surface Expression Are Well-Conserved Functions of Human and Simian Immunodeficiency Virus nef Alleles. J. Virol. 77: 10548-10556 [Abstract] [Full Text]  
• Sugimoto, C., Tadakuma, K., Otani, I., Moritoyo, T., Akari, H., Ono, F., Yoshikawa, Y., Sata, T., Izumo, S., Mori, K. (2003). nef Gene Is Required for Robust Productive Infection by Simian Immunodeficiency Virus of T-Cell-Rich Paracortex in Lymph Nodes. J. Virol. 77: 4169-4180 [Abstract] [Full Text]  
• Kasper, M. R., Collins, K. L. (2003). Nef-Mediated Disruption of HLA-A2 Transport to the Cell Surface in T Cells. J. Virol. 77: 3041-3049 [Abstract] [Full Text]  
• Williams, M., Roeth, J. F., Kasper, M. R., Fleis, R. I., Przybycin, C. G., Collins, K. L. (2002). Direct Binding of Human Immunodeficiency Virus Type 1 Nef to the Major Histocompatibility Complex Class I (MHC-I) Cytoplasmic Tail Disrupts MHC-I Trafficking. J. Virol. 76: 12173-12184 [Abstract] [Full Text]  
• Munch, J., Janardhan, A., Stolte, N., Stahl-Hennig, C., ten Haaft, P., Heeney, J. L., Swigut, T., Kirchhoff, F., Skowronski, J. (2002). T-Cell Receptor:CD3 Down-Regulation Is a Selected In Vivo Function of Simian Immunodeficiency Virus Nef but Is Not Sufficient for Effective Viral Replication in Rhesus Macaques. J. Virol. 76: 12360-12364 [Abstract] [Full Text]  
• Patel, P. G., Yu Kimata, M. T., Biggins, J. E., Wilson, J. M., Kimata, J. T. (2002). Highly Pathogenic Simian Immunodeficiency Virus mne Variants That Emerge during the Course of Infection Evolve Enhanced Infectivity and the Ability To Downregulate CD4 but Not Class I Major Histocompatibility Complex Antigens. J. Virol. 76: 6425-6434 [Abstract] [Full Text]  
• Lundquist, C. A., Tobiume, M., Zhou, J., Unutmaz, D., Aiken, C. (2002). Nef-Mediated Downregulation of CD4 Enhances Human Immunodeficiency Virus Type 1 Replication in Primary T Lymphocytes. J. Virol. 76: 4625-4633 [Abstract] [Full Text]  

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Münch, J. Articles by Kirchhoff, F. Search for Related Content PubMed PubMed Citation Articles by Münch, J. Articles by Kirchhoff, F.