PERSPECTIVE
Cytomegalovirus Infection
Regulation of Inflammation

Gary W. Hunninghake, Martha M. Monick, and Lois J. Geist

University of Iowa College of Medicine, Iowa City, Iowa

Cytomegalovirus (CMV) is an important cause of infection in immunocompromised patients (1). The two groups that most frequently have clinical infections with CMV are patients infected with the human immunodeficiency virus (HIV) and patients with transplanted organs. CMV can infect many different organ systems, and it is a significant cause of morbidity for patients with HIV infection. CMV infections in patients who have undergone organ transplantation may be an important cause of life-threatening pneumonia and other infections. In addition, CMV has a tendency to infect transplanted organs and trigger rejection. In this regard, CMV infection in a previously seronegative lung transplant recipient is associated with a greater likelihood for the development of severe obliterative bronchiolitis.

There appears to be a greater incidence of CMV infection in patients who have received a transplanted organ compared with patients who are equally immunosuppressed but have not undergone organ transplantation. This clinical observation could be explained by observations that suggest that CMV replicates best in cells that are activated. One by-product of organ transplantation is an intense activation of the immune system in an attempt to reject the transplanted organ. Other cells, like endothelial cells, fibroblasts, and epithelial cells may also be activated by cytokines released by activated inflammatory cells. This cell activation is most intense in the transplanted organ. Thus, the setting of organ transplantation creates an ideal environment for replication of CMV.

Although the control of CMV replication is not entirely understood, it is known that replication is under control of the CMV major immediate early promoter, which controls expression of viral immediate early genes. Expression of the immediate early genes is important for viral replication because the products of these genes are transcription factors necessary for expression of other viral genes. Cell activation is crucial for viral replication because the virus does not express the genes that encode some of the critical transcription factors necessary to activate the major immediate early promoter. Two of the most important of these transcription factors are nuclear factor (NF)B and cyclic adenosine monophosphate (cAMP)-dependent transcription factors. These transcription factors are expressed at high levels in cells that are activated. Thus, the virus is highly dependent on activation of the infected cell for replication of its genome (Figure 1).

View larger version (16K): [in this window] [in a new window]   Figure 1.   Cell activation is critical for viral replication. Activation of the cell provides critical cell-derived transcription factors (like NFB and cAMP-derived transcription factors), which are necessary for enhanced expression of the CMV major immediate early promoter. The major immediate early promoter controls viral replication. One function of the virally encoded US28 gene product might be to enhance viral replication because prior studies have shown that it is a signaling receptor that results in cell activation after exposure to chemokines.

The mechanisms by which CMV regulates inflammation are very complex (6). There are at least two general ways that CMV can stimulate cells. One mechanism involves attachment of CMV to the cell surface, which results in stimulation of the cell via viral surface glycoproteins. A number of viral coat proteins that mediate attachment to and activation of various types of cells have been identified. This means of cell stimulation probably occurs during active infection. It has also been demonstrated that expression of the viral immediate early genes, in the absence of viral replication, also results in cell activation. Expression of the immediate early genes of CMV occurs during active infection, but it can also occur during latency in the absence of viral replication. The latter observation suggests that latent CMV infection can alter inflammatory responses by cells that contain the viral genome. These observations are also consistent with clinical observations that drugs that inhibit viral replication do not inhibit all of the observed effects of CMV.

There are a number of specific ways that CMV may activate cells (6). CMV infection may increase or decrease expression of classes I or II human leukocyte antigen (HLA) antigens. Inhibition of expression of class I antigens by CMV has been proposed as a mechanism used by the virus to escape immune surveillance. By contrast, upregulation of class II antigens has been proposed as mechanisms by which CMV triggers enhanced graft rejection. CMV has also been shown to increase expression of adherence proteins, like intracellular adhesion molecule-1 (ICAM-1) (CD54) and lymphocyte function-associated antigen (LFA)-3 (CD58), and expression of a variety of cytokine genes by monocytes, lymphocytes, epithelial cells, endothelial cells, and fibroblasts. Others studies have shown that epitopes on the CMV IE2 gene product mimic peptides on HLA DR3 antigens (24). This observation suggests that CMV infection might, in some instances, trigger an autoimmune-type disease. Overall, these observations strongly suggest that CMV can augment inflammatory processes. That this can occur in the lung is suggested by an observation that the combination of graft-versus-host disease (GVHD) and CMV can result in interstitial lung disease in animal models. Neither GVHD alone nor CMV alone resulted in lung disease. Although these observations do not eliminate the possibility that GVHD alone can cause lung disease, they do suggest that CMV may increase the expression of this type of lung disorder.

An interesting observation from a number of studies is that the viral genome encodes a number of receptors, including HLA-like antigens that can bind to -2-microglobulin, Fc receptors, and receptors for various cytokines and chemokines (25). In this issue of the Journal, Billstrom and colleagues (41) show that the CMV-encoded chemokine receptor, US28, depletes extracellular regulated upon activation, normal T-cells expressed and secreted (RANTES) during CMV infection. A number of investigators have previously shown that the CMV genome contains four genes (US27, US28, UL33, and UL78) that encode putative homologues of cellular G protein-coupled receptors (25). Of these, the US28 gene product has been shown to be a functional receptor for the -chemokine class of immune modulators. It has also previously been demonstrated that the US28 gene product is a signaling receptor that activates cells and can deplete the extracellular medium of RANTES. The present study by Billstrom and associates extends these observations by providing a mechanism for the depletion of this cytokine. The authors suggest that this may be one mechanism through which CMV might regulate inflammation. Since HIV also utilizes chemokine receptors for infection, the authors also speculate that this might alter the ability of HIV to infect cells. Although these observations are probably the case, the question is why the virus might have evolved to express this receptor. It is unlikely that uptake of RANTES is a protective mechanism for the virus because high levels of RANTES are usually present at sites of infection in spite of this uptake by the cells. More likely, expression of this receptor is important for viral replication, since an interaction of this receptor with its ligand results in cell activation. As noted previously, this is a critical process for viral replication. These observations as a whole are important because they may lead to new, more specific therapies for this important infection.

	Footnotes

Address correspondence to: Gary W. Hunninghake, M.D., Pulmonary Division, Room C33G-GH, University of Iowa College of Medicine, 200 Hawkins Dr., Iowa City, IA 52242. E-mail: gary-hunninghake{at}uiowa.edu

(Received in original form May 29, 1999).

	References

1. Girgis, R. E., I. Tu, G. J. Berry, H. Reichenspurner, V. G. Valentine, J. V. Conte, A. Ting, I. Johnstone, J. Miller, R. C. Robbins, B. A. Reitz, and J. Theodore. 1996. Risk factors for the development of obliterative bronchiolitis after lung transplantation. J. Heart Lung Transplant. 15: 1200-1208 [Medline].

2. Hertz, M. I., C. Jordan, S. K. Savik, J. M. Fox, S. Park, R. M. Bolman III, and B. M. Dosland-Mullan. 1998. Randomized trial of daily versus three-times-weekly prophylactic ganciclovir after lung and heart-lung transplantation. J. Heart Lung Transplant. 17: 913-920 [Medline].

3. Lemstrom, K., E. Kallio, R. Krebs, C. Bruggeman, P. Hayry, and P. Koskinen. 1996. Cytomegalovirus infection accelerates obliterative bronchiolitis of rat tracheal allografts. Transpl. Int. 9: S221-S222 .

4. Reichenspurner, H., V. Soni, M. Nitschke, G. J. Berry, T. Brazelton, R. Shorthouse, X. Huang, J. Boname, R. Girgis, B. A. Raitz, E. Mocarski, G. Sandford, and R. E. Morris. 1998. Enhancement of obliterative airway disease in rat tracheal allografts infected with recombinant rat cytomegalovirus. J. Heart Lung Transplant. 17: 439-451 [Medline].

5. Smith, M. A., S. Sundaresan, T. Mohanakumar, E. P. Trulock, J. P. Lynch, D. L. Phelan, J. D. Cooper, and G. A. Patterson. 1998. Effect of development of antibodies to HLA and cytomegalovirus mismatch on lung transplantation survival and development of bronchiolitis obliterans syndrome. J. Thorac. Cardiovasc. Surg. 116: 812-820 [Abstract/Free Full Text].

6. Burns, L. J., J. C. Pooley, D. J. Walsh, G. M. Vercellotti, M. L. Weber, and A. Kovacs. 1999. Intercellular adhesion molecule-1 expression in endothelial cells is activated by cytomegalovirus immediate early proteins [see comments]. Transplantation 67: 137-144 [Medline].

7. Craigen, J. L., and J. E. Grundy. 1996. Cytomegalovirus induced up-regulation of LFA-3 (CD58) and ICAM-1 (CD54) is a direct viral effect that is not prevented by ganciclovir or foscarnet treatment. Transplantation 62: 1102-1108 [Medline].

8. Fletcher, J. M., H. G. Prentice, and J. E. Grundy. 1998. Natural killer cell lysis of cytomegalovirus (CMV)-infected cells correlates with virally induced changes in cell surface lymphocyte function-associated antigen-3 (LFA-3) expression and not with the CMV-induced down-regulation of cell surface class I HLA. J. Immunol. 161: 2365-2374 [Abstract/Free Full Text].

9. Geist, L. J., M. M. Monick, M. F. Stinski, and G. W. Hunninghake. 1991. The immediate early genes of human cytomegalovirus upregulate expression of the interleukin-2 and interleukin-2 receptor genes. Am. J. Respir. Cell Mol. Biol. 5: 292-296 .

10. Geist, L. J., M. M. Monick, M. F. Stinski, and G. W. Hunninghake. 1992. Cytomegalovirus immediate early genes prevent the inhibitory effect of cyclosporin A on interleukin 2 gene transcription. J. Clin. Invest. 90: 2136-240 .

11. Hahn, G., R. Jores, and E. S. Mocarski. 1998. Cytomegalovirus remains latent in a common precursor of dendritic and myeloid cells. Proc. Natl. Acad. Sci. USA 95: 3937-3942 [Abstract/Free Full Text].

12. Hirsch, A. J., and T. Shenk. 1999. Human cytomegalovirus inhibits transcription of the CC chemokine MCP-1 gene. J. Virol. 73: 404-410 [Abstract/Free Full Text].

13. Hopkins, H. A., M. M. Monick, and G. W. Hunninghake. 1996. Cytomegalovirus inhibits CD14 expression on human alveolar macrophages. J. Infect. Dis. 174: 69-74 [Medline].

14. Hunninghake, G. W., M. M. Monick, B. Liu, and M. F. Stinski. 1989. The promoter-regulatory region of the major immediate-early gene of human cytomegalovirus responds to T-lymphocyte stimulation and contains functional cyclic AMP-response elements. J. Virol. 63: 3026-3033 [Abstract/Free Full Text].

15. Iwamoto, G. K., M. M. Monick, B. D. Clark, P. E. Auron, M. F. Stinski, and G. W. Hunninghake. 1990. Modulation of interleukin 1 beta gene expression by the immediate early genes of human cytomegalovirus. J. Clin. Invest. 85: 1853-1857 .

16. Michelson, S., P. Dal, Monte, D. Zipeto, B. Bodaghi, L. Laurent, E. Oberlin, F. Arenzana-Seisdedos, J. L. Virelizier, and M. P. Landini. 1997. Modulation of RANTES production by human cytomegalovirus infection of fibroblasts. J. Virol. 71: 6495-6500 [Abstract].

17. Miller, D. M., B. M. Rahill, J. M. Boss, M. D. Lairmore, J. E. Durbin, J. W. Waldman, and D. D. Sedmak. 1998. Human cytomegalovirus inhibits major histocompatibility complex class II expression by disruption of the Jak/ Stat pathway. J. Exp. Med. 187: 675-683 [Abstract/Free Full Text].

18. Monti, G., A. Magnan, M. Fattal, B. Rain, M. Humbert, J. L. Mege, M. Noirclerc, P. Dartevelle, J. Cerrina, G. Simonneau, P. Galanaud, and D. Emilie. 1996. Intrapulmonary production of RANTES during rejection and CMV pneumonitis after lung transplantation. Transplantation 61: 1757-1762 [Medline].

19. Murayama, T., K. Kuno, F. Jisaki, M. Obuchi, D. Sakamuro, T. Furukawa, N. Mukaida, and K. Matsushima. 1994. Enhancement of human cytomegalovirus replication in a human lung fibroblast cell line by interleukin-8. J. Virol. 68: 7582-7585 [Abstract/Free Full Text].

20. Sparrelid, E., D. Emanuel, T. Fehniger, U. Andersson, and J. Andersson. 1997. Interstitial pneumonitis in bone marrow transplant recipients is associated with local production of Th2-type cytokines and lack of T cell-mediated cytotoxicity. Transplantation 63: 1782-1789 [Medline].

21. Taichman, R. S., M. R. Nassiri, M. J. Reilly, R. G. Ptak, S. G. Emerson, and J. C. Drach. 1997. Infection and replication of human cytomegalovirus in bone marrow stromal cells: effects on the production of IL-6, MIP-1, and TGF- 1. Bone Marrow Transplant 19: 471-480 [Medline].

22. You, X. M., C. Steinmuller, T. O. Wagner, C. A. Bruggeman, A. Haverich, and G. Steinhoff. 1996. Enhancement of cytomegalovirus infection and acute rejection after allogeneic lung transplantation in the rat: virus-induced expression of major histocompatibility complex class II antigens. J. Heart Lung Transplant. 15: 1108-1119 [Medline].

23. Yurochko, A. D., E. S. Hwang, L. Rasmussen, S. Keay, L. Pereira, and E. S. Huang. 1997. The human cytomegalovirus UL55 (gB) and UL75 (gH) glycoprotein ligands initiate the rapid activation of Sp1 and NF-kappaB during infection. J. Virol. 71: 5051-5059 [Abstract].

24. Fujinami, R. S., J. A. Nelson, L. Walker, and M. B. Oldstone. 1988. Sequence homology and immunologic cross-reactivity of human cytomegalovirus with HLA-DR beta chain: a means for graft rejection and immunosuppression. J. Virol. 62: 100-105 [Abstract/Free Full Text].

25. Beck, S., and B. G. Barrell. 1988. Human cytomegalovirus encodes a glycoprotein homologous to MHC class-I antigens. Nature 331: 269-272 [Medline].

26. Boyle, K. A., and T. Compton. 1998. Receptor-binding properties of a soluble form of human cytomegalovirus glycoprotein B.  J. Virol. 72: 1826-1833 [Abstract/Free Full Text].

27. Grundy, J. E., J. A. McKeating, and P. D. Griffiths. 1987. Cytomegalovirus strain AD169 binds beta 2 microglobulin in vitro after release from cells. J. Gen. Virol. 68: 777-784 [Abstract/Free Full Text].

28. Grundy, J. E., J. A. McKeating, P. J. Ward, A. R. Sanderson, and P. D. Griffiths. 1987. Beta 2 microglobulin enhances the infectivity of cytomegalovirus and when bound to the virus enables class I HLA molecules to be used as a virus receptor. J. Gen. Virol. 68: 793-803 [Abstract/Free Full Text].

29. MacCormac, L. P., and J. E. Grundy. 1996. Human cytomegalovirus induces an Fc gamma receptor (FcgammaR) in endothelial cells and fibroblasts that is distinct from the human cellular FcgammaRs. J. Infect. Dis. 174: 1151-1161 [Medline].

30. Stannard, L. M., and D. R. Hardie. 1991. An Fc receptor for human immunoglobulin G is located within the tegument of human cytomegalovirus. J. Virol. 65: 3411-3415 [Abstract/Free Full Text].

31. Billstrom, M. A., G. L. Johnson, N. J. Avdi, and G. S. Worthen. 1998. Intracellular signaling by the chemokine receptor US28 during human cytomegalovirus infection. J. Virol. 72: 5535-5544 [Abstract/Free Full Text].

32. Bodaghi, B., T. R. Jones, D. Zipeto, C. Vita, L. Sun, L. Laurent, F. Arenzana-Seisdedos, J. L. Virelizier, and S. Michelson. 1998. Chemokine sequestration by viral chemoreceptors as a novel viral escape strategy: withdrawal of chemokines from the environment of cytomegalovirus-infected cells. J. Exp. Med. 188: 855-866 [Abstract/Free Full Text].

33. Gao, J. L., D. B. Kuhns, H. L. Tiffany, D. McDermott, X. Li, U. Francke, and P. M. Murphy. 1993. Structure and functional expression of the human macrophage inflammatory protein 1 alpha/RANTES receptor. J. Exp. Med. 177: 1421-1427 [Abstract/Free Full Text].

34. Gao, J. L., and P. M. Murphy. 1994. Human cytomegalovirus open reading frame US28 encodes a functional beta chemokine receptor. J. Biol. Chem. 269: 28539-28542 [Abstract/Free Full Text].

35. Kledal, T. N., M. M. Rosenkilde, and T. W. Schwartz. 1998. Selective recognition of the membrane-bound CX3C chemokine, fractalkine, by the human cytomegalovirus-encoded broad-spectrum receptor US28. FEBS Lett. 441: 209-214 [Medline].

36. Kuhn, D. E., C. J. Beall, and P. E. Kolattukudy. 1995. The cytomegalovirus US28 protein binds multiple CC chemokines with high affinity. Biochem. Biophys. Res. Commun. 211: 325-330 [Medline].

37. Neote, K., D. DiGregorio, J. Y. Mak, R. Horuk, and T. J. Schall. 1993. Molecular cloning, functional expression, and signaling characteristics of a C-C chemokine receptor. Cell 72: 415-425 [Medline].

38. Pleskoff, O., C. Treboute, and M. Alizon. 1998. The cytomegalovirus-encoded chemokine receptor US28 can enhance cell-cell fusion mediated by different viral proteins. J. Virol. 72: 6389-6397 [Abstract/Free Full Text].

39. Vieira, J., T. J. Schall, L. Corey, and A. P. Geballe. 1998. Functional analysis of the human cytomegalovirus US28 gene by insertion mutagenesis with the green fluorescent protein gene. J. Virol. 72: 8158-8165 [Abstract/Free Full Text].

40. Welch, A. R., L. M. McGregor, and W. Gibson. 1991. Cytomegalovirus homologs of cellular G protein-coupled receptor genes are transcribed. J. Virol. 65: 3915-3918 [Abstract/Free Full Text].

41. Billstrom, M., L. Lehman, and G. Worthen. 1999. Depletion of extracellular RANTES during human cytomegalovirus infection of endothelial cells. Am. J. Respir. Cell Mol. Biol. 21: 163-167 [Abstract/Free Full Text].