Pentoxifylline Promotes Replication of Human Cytomegalovirus In Vivo and In Vitro

Inhibition of human cytomegalovirus replication by overexpression of CREB1

Expression of the human cytomegalovirus (HCMV) major immediate-early (MIE) genes is regulated by a strong enhancer-containing promoter with multiple binding sites for various transcription factors, including cyclic AMP response element binding protein 1 (CREB1). Here we show that overexpression of CREB1 potently blocked MIE transcription and HCMV replication. Surprisingly, CREB1 still exhibited strong inhibition of the MIE promoter when all five CREB binding sites within the enhancer were mutated, suggesting that CREB1 regulated the MIE gene expression indirectly. Promoter deletion analysis and site-directed mutagenesis identified the region between -130 and -50 upstream of the transcription start site of the MIE gene as the "CREB1 responsive region". Mutations of SP1/3 and NF-κB binding sites within this region interrupted the inhibitory effect induced by CREB1 overexpression. Our findings suggest that overexpression of CREB1 can cause repression of HCMV replication and may contribute to the development of new anti-HCMV strategies.

Schizophrenia susceptibility genes directly implicated in the life cycles of pathogens: cytomegalovirus, influenza, herpes simplex, rubella, and Toxoplasma gondii

Many genes implicated in schizophrenia can be related to glutamatergic transmission and neuroplasticity, oligodendrocyte function, and other families clearly related to neurobiology and schizophrenia phenotypes. Others appear rather to be involved in the life cycles of the pathogens implicated in the disease. For example, aspartylglucosaminidase (AGA), PLA2, SIAT8B, GALNT7, or B3GAT1 metabolize chemical ligands to which the influenza virus, herpes simplex, cytomegalovirus (CMV), rubella, or Toxoplasma gondii bind. The epidermal growth factor receptor (EGR/EGFR) is used by the CMV to gain entry to cells, and a CMV gene codes for an interleukin (IL-10) mimic that binds the host cognate receptor, IL10R. The fibroblast growth factor receptor (FGFR1) is used by herpes simplex. KPNA3 and RANBP5 control the nuclear import of the influenza virus. Disrupted in schizophrenia 1 (DISC1) controls the microtubule network that is used by viruses as a route to the nucleus, while DTNBP1, MUTED, and BLOC1S3 regulate endosomal to lysosomal routing that is also important in viral traffic. Neuregulin 1 activates ERBB receptors releasing a factor, EBP1, known to inhibit the influenza virus transcriptase. Other viral or bacterial components bind to genes or proteins encoded by CALR, FEZ1, FYN, HSPA1B, IL2, HTR2A, KPNA3, MED12, MED15, MICB, NQO2, PAX6, PIK3C3, RANBP5, or TP53, while the cerebral infectivity of the herpes simplex virus is modified by Apolipoprotein E (APOE). Genes encoding for proteins related to the innate immune response, including cytokine related (CCR5, CSF2RA, CSF2RB, IL1B, IL1RN, IL2, IL3, IL3RA, IL4, IL10, IL10RA, IL18RAP, lymphotoxin-alpha, tumor necrosis factor alpha [TNF]), human leukocyte antigen (HLA) antigens (HLA-A10, HLA-B, HLA-DRB1), and genes involved in antigen processing (angiotensin-converting enzyme and tripeptidyl peptidase 2) are all concerned with defense against invading pathogens. Human microRNAs (Hsa-mir-198 and Hsa-mir-206) are predicted to bind to influenza, rubella, or poliovirus genes. Certain genes associated with schizophrenia, including those also concerned with neurophysiology, are intimately related to the life cycles of the pathogens implicated in the disease. Several genes may affect pathogen virulence, while the pathogens in turn may affect genes and processes relevant to the neurophysiology of schizophrenia. For such genes, the strength of association in genetic studies is likely to be conditioned by the presence of the pathogen, which varies in different populations at different times, a factor that may explain the heterogeneity that plagues such studies. This scenario also suggests that drugs or vaccines designed to eliminate the pathogens that so clearly interact with schizophrenia susceptibility genes could have a dramatic effect on the incidence of the disease.

Pentoxifylline down modulate in vitro T cell responses and attenuate pathology in Leishmania and HTLV-I infections

Tumor necrosis factor-alpha (TNF-alpha) is known to have numerous biological properties relating to inflammation. This cytokine participates in the tissue damage of chronic inflammatory, autoimmune and infectious diseases. Pentoxifylline is a methylxanthine that inhibits phosphodiesterase IV, which inhibits the degradation of the cAMP and prostanoids. The increased intracellular concentration of the cAMP leads to a negative regulation of NF-kappaB and NF-AT transcription factors and suppresses TNF-alpha production. This review describes studies that support evidences that TNF-alpha is involved in the pathogenesis of HTLV-1 associated myelopathy and of cutaneous and mucosal leishmaniasis. Additionally, it demonstrates the effect of pentoxifylline in vitro in inhibiting TNF-alpha and IFN-gamma spontaneous production in PBMC from HTLV-1-infected patients, as well as its in vivo effect in inhibiting TNF-alpha in sera from mucosal leishmaniasis patients. Moreover, we review the results of clinical studies from the last 10 years using pentoxifylline to treat HTLV-1 associated myelopathy and cutaneous and mucosal leishmaniasis.

Viral infection in the renal transplant recipient

Viruses are among the most common causes of opportunistic infection after transplantation and the most important. The risk for viral infection is a function of the specific virus encountered, the intensity of immune suppression used to prevent graft rejection, and other host factors governing susceptibility. Viral infection, both symptomatic and asymptomatic, causes the "direct effects" of invasive disease and "indirect effects," including immune suppression predisposing to other opportunistic infections and oncogenesis. Rapid and sensitive microbiologic assays for many of the common viruses after transplantation have replaced, for the most part, serologic testing and in vitro cultures for the diagnosis of infection. Furthermore, quantitative molecular tests allow the individualization of antiviral therapies for prevention and treatment of infection. This advance is most prominent in the management of cytomegalovirus, Epstein-Barr, hepatitis B, and hepatitis C viruses. Diagnostic advances have not been accompanied by the development of specific and nontoxic anti-viral agents or effective antiviral vaccines. Vaccines, where available, should be given to patients as early as possible and well in advance of transplantation to optimize the immune response. Studies of viral latency, reactivation, and the cellular effects of viral infection will provide clues for future strategies in prevention and treatment of viral infections.

Subclinical activation of latent cytomegalovirus (CMV) infection and anti-CMV immune response in patients with atopic dermatitis

BACKGROUND

Microbiological infections are considered to be of pathophysiological importance in atopic dermatitis (AD). As yet, no information is available regarding cytomegalovirus (CMV) infection in this disease. This, however, is of interest because of the high prevalence of latent infections in the general population, the frequent reactivation in inflammatory diseases, and the immunomodulating capacity of CMV.

OBJECTIVES

To investigate the prevalence of latent CMV infection, the frequency of active CMV infection, and the immune response to CMV in patients with moderate to severe AD. Methods To detect active infection we analysed CMV antigen expression by peripheral blood mononuclear cells (PBMC) from 27 patients with moderate to severe AD in comparison with 53 healthy volunteers. We used three monoclonal antibodies recognizing different CMV-encoded antigens and immunocytological staining (alkaline phosphatase-antialkaline phosphatase technique).

RESULTS

Patients with AD had a higher mean frequency of CMV-positive PBMC: 2.25 per 10 000 vs. 0.74 per 10 000 in controls (P = 0.001) as well as a higher incidence of CMV antigenaemia: 29.6% vs. 7.5% (P < 0.01). Seropositivity for anti-CMV IgG antibodies indicated subclinical activation of latent infection. Remarkably, a clearance of CMV antigenaemia was observed during anti-eczematous treatment. Significantly higher plasma levels of tumour necrosis factor-alpha, which is involved in CMV reactivation, and interleukin-12, which is crucial for an antiviral cellular immune response, were observed in AD patients in comparison with healthy volunteers. Furthermore, a significantly enhanced frequency of circulating activated HLA-DR+ T cells especially in CMV-seropositive AD patients (19.3% vs. 13.5% in seronegative AD patients vs. 10.2% in controls) suggested that the active CMV infection triggers a cellular immune response. This was also supported by a high frequency of CMV-specific interferon-gamma-producing T cells in CMV-seropositive patients with AD.

CONCLUSIONS

Our data suggest that active, subclinical CMV infection is more frequent in patients with moderate to severe AD and may have immunopathophysiological relevance.

NF-kappaB--a potential therapeutic target for inhibition of human cytomegalovirus (re)activation?

From clinical studies the proinflammatory cytokine TNFalpha was proposed to play a key role in human cytomegalovirus (HCMV) reactivation from latency. In vitro experiments confirmed that TNFalpha stimulates the activity of the HCMV IE1/2 enhancer/promoter, which controls immediate early protein IE1 and IE2 gene expression via activation of the transcription factor NF-kappaB and its binding to putative binding sites in the IE1/2 enhancer. NF-kappaB was also proposed to be involved in IE1-mediated autostimulation of this promoter. The IE1/2 enhancer of HCMV contains four putative NF-kappaB binding sites which differ in their distance to the transcription start site as well as in their sequence. Construction and testing of a series of promoter mutants demonstrated that NF-kappaB is essential for both TNFalpha and IE1 stimulation. Furthermore, we were able to show that although all four NF-kappaB sites bind NF-kappaB with similar affinity in vitro, the contribution to TNFalpha and IE1 stimulation differs in correlation with the distance to the transcription start site and the sequence. Site 1 and 3 play the most dominant role and site 2 an intermediate, while site 4, which is conserved in sequence but far distant from the transcription start site, had no influence on NF-kappaB-mediated regulation of the IE1/2 promoter. Specific inhibition of NF-kappaB signalling by co-expression of a dominant-negative IkappaB variant reduced TNFalpha stimulation of the IE1/2 enhancer/promoter by up to 80%. From this data, inhibitors of NF-kappaB activation are suggested to be an alternative therapeutical strategy to interfere with HCMV (re)activation in undifferentiated monocyte/granulocyte progenitor cells in patients with a high risk of inflammation-related HCMV (re)activation.

Timing of pentoxifylline treatment determines its protective effect on diabetes development in the Bio Breeding rat

Diabetes-prone Bio Breeding (DP-BB) rats spontaneously develop diabetes between 60 and 120 days of age. Diabetes-resistant (DR)-BB rats can be induced to develop diabetes by poly(I:C) and anti-RT6. Here, we studied the effect of pentoxifylline, a potent anti-inflammatory agent, on diabetes development in both BB rat models of insulin-dependent diabetes mellitus and investigated whether these effects were related to differential modulation of tumour necrosis factor (TNF)-alpha and interleukin-10. When DP-BB rats received pentoxifylline from day 60 onwards, diabetes development was delayed and reduced. The other treatment protocols had no effect. In DR-BB rats, pentoxifylline treatment resulted only in a delay of diabetes development. In both BB rat models, in vivo pentoxifylline treatment potently suppressed TNF-alpha, but only moderately affected interleukin-10 production in vitro. These results show that timing of pentoxifylline treatment determines its protective effect on diabetes development in DP-BB rats. The observed pentoxifylline-induced increase of the interleukin-10/TNF-alpha ratio might be a mechanism for protection or delay of the diabetes development.

Pattern and persistence of the epitope-specific IgM response against human cytomegalovirus in renal transplant patients

The humoral immune response against human cytomegalovirus (HCMV) was evaluated in immunocompromised patients by Western blotting (WB) based on recombinant viral envelope (gB and gH) and tegument (pp150 and pp65) proteins. Three groups of patients were investigated: (a) 74 renal transplant recipients; (b) 24 hemodialysis patients, both groups without clinical evidence of viral infections; and (c) 19 renal transplant patients with manifest HCMV infections. The results obtained suggest that (i) the WB is considerably more sensitive, recognizing the HCMV-specific IgM response rather than the enzyme-linked immunosorbent assays. An IgM response was detected in one-third of all clinically asymptomatic renal patients. (ii) The virus-specific IgM response is primarily directed against the pp150 epitope. (iii) In patients with clinically manifest HCMV disease, additional IgM reactivities are most frequently directed against the glycoprotein B epitope. (iv) The severity of HCMV infections correlates with the extent of the IgM antibody response, i.e. with the number of specific epitopes involved. (v) After transplantation, IgM reactivity and its epitope-specific pattern persist for years.

A novel link between stress and human cytomegalovirus (HCMV) infection: sympathetic hyperactivity stimulates HCMV activation

Recently, inflammatory mediators such as TNFalpha were identified as triggering active human cytomegalovirus (HCMV) infection. Here, we demonstrate that a highly stressful event in the absence of systemic inflammation, as observed in patients with acute myocardial infarction, leads to the development of an active HCMV infection in latently infected patients. Elucidating the molecular mechanism of virus activation, we could show that catecholamines directly stimulate the HCMV immediate-early (IE) enhancer/promoter in monocytic cells via beta-2 adrenergic receptors. Subsequent activation of the cAMP/PK-A-signaling pathway results in enhanced synthesis and binding of the transcription factor CREB-1/ATF-1 to the cAMP-responsive elements within the IE enhancer. Epinephrine also enhanced HCMV gene expression in infected THP-1 cells by about 50% in three of four experiments. These data suggest that HCMV, like HSV-1 and VZV, can be (re)activated under stress conditions.

Catecholamines trigger IL-10 release in acute systemic stress reaction by direct stimulation of its promoter/enhancer activity in monocytic cells

Acute stress reactions (e.g. linked with trauma, major surgery, psychic stress and myocardial infarction) are accompanied with temporary systemic release of the anti-inflammatory cytokine IL-10 followed by immunodepression. Since an association between activation of the sympathetic system and IL-10 release has been described, we studied the influence of catecholamines on its promoter activity in vitro. Using reporter gene assays we demonstrated that catecholamines in monocytic cells directly stimulate the IL-10 promoter/enhancer via a cAMP/protein kinase A-dependent pathway. A cAMP responsive element was identified as major target. Thus, catecholamines are directly involved in the regulation of immunoresponsiveness under stressful conditions.

Immunomodulatory effect of pentoxifylline during human allograft rejection: involvement of tumor necrosis factor-alpha and adhesion molecules

BACKGROUND

Pentoxifylline (PTX), a methylxanthine phosphodiesterase inhibitor, is poorly active as an immunosuppressant but prevents the synthesis of proinflammatory cytokines. In a randomized double-blind study comparing PTX versus placebo in 140 patients receiving cadaveric kidney grafts under cyclosporine and prednisone, we have shown that PTX weakened the consequences of rejection on graft survival. To assess the mechanism underlying the beneficial effect recorded during this trial, we analyzed the impact of PTX on tumor necrosis factor (TNF-alpha) production and expression of cell adhesion molecules.

METHODS

Plasma levels of TNF-alpha and its soluble receptors (sTNF-RI, sTNF-RII) and of soluble vascular cell adhesion molecule 1 (sVCAM-1) were monitored over the 6 months postgraft period when PTX or placebo were administered. Expression of VCAM-1 and intercellular cell adhesion molecule 1 was scored by immunohistochemical staining of biopsy specimens from patients who underwent rejection crisis. Lymphocyte subset composition was analyzed longitudinally during cytomegalovirus (CMV) infections.

RESULTS

Plasma TNF-alpha levels were significantly reduced in the PTX-treated group over the 6 months of administration, and specifically during isolated rejection episodes and during CMV infections. Plasma levels of sTNFR-I, sTNFR-II, and sVCAM-1 did not differ between the two groups of patients, but a decrease in renal tubular VCAM-1 expression was observed in the PTX group. During CMV infections, CD8 lymphocytosis and expansion of CD57+ (CD28-) CD8+ T cells were similar in the two groups.

CONCLUSION

The data collected during this double-blind study point to an immunomodulatory role of PTX, the beneficial effect on graft survival resulting from a restraining effect of the drug on the inflammatory conditions involved in acute graft rejection.

Cyclic adenosine monophosphate-responsive elements are involved in the transcriptional activation of the human IL-10 gene in monocytic cells

IL-10 plays an important role in the regulation of immune responses. We and others have demonstrated recently that cyclic adenosine monophosphate (cAMP)-elevating substances up-regulate monocytic IL-10 expression in vitro and in vivo. Computer analysis of the IL-10 promoter/enhancer region localized four putative cAMP-responsive elements (CRE1- 4) with homology to the CRE consensus motif. In electrophoretic mobility shift assays CRE1 and CRE4 bound protein complexes consisting of transcription factors CREB-1 and ATF-1, while CRE3 bound only marginal amounts of CREB-1/ATF-1 in combination with unknown protein(s). CRE2 showed no protein binding activity. In vitro mutation of CRE1 and CRE4 reduced the level of cAMP-stimulated transactivation in reporter gene assays in comparison to the wild-type promoter by 20 % and 50 %, respectively, while mutation of CRE3 had no effect. The main action of CRE4 on cAMP-dependent stimulation is probably based on its adjacent localization to the TATA box and its sequence comprising a perfect half site. Experiments with double and triple mutants and with deleted promoter fragments indicated the participation of additional elements beside the CRE motifs in the cAMP-dependent stimulation. Our data suggest that intracellular cAMP may directly affect expression of the immunoregulatory cytokine IL-10 in monocytic cells via activation of the eukaryotic transcription factors CREB-1 and ATF-1 and their binding to CRE1 and CRE4 in the upstream enhancer of the IL-10 promoter.

Mechanisms of human cytomegalovirus (HCMV) (re)activation and its impact on organ transplant patients

Human cytomegalovirus (HCMV) infection plays an important role in transplant patients. Its impact is both direct and indirect. This review focuses on new aspects of HCMV (re)activation and HCMV related pathology, particularly HCMV-associated renal allograft injury. During the last two years we have learned that HCMV is more frequently (re)activated, even in healthy people, than previously expected. Inflammatory as well as stress mediators and some drugs may (re)activate the virus by using distinct intracellular pathways. Commonly, HCMV (re)activation is accompanied by HCMV antigenemia/DNAemia, suggesting that precursor cells in the bone marrow play an important role as a reservoir of latent virus. However, local HCMV (re)activation (colon, lung) without detection of active HCMV infection in the peripheral blood is possible. In healthy people a sufficient type 1 T-cell response controls the active HCMV infection, while in patients with severe immune deficiency (AIDS, high-dose immunosuppression) the virus can spread in an uncontrolled fashion and induce 'classic' HCMV disease. In patients with moderate immune deficiency (e.g. long-term transplant patients on low-dose immunosuppression) virus spreading is controlled but the elimination of cells harboring the active virus may be insufficient. The resulting persistent HCMV antigenemia may induce chronic inflammatory processes leading to tissue injury, particularly in the allograft. Therefore, antiviral therapy may be useful in patients suffering from graft deterioration with otherwise clinically symptomless HCMV infection. HCMV-related immune deficiency with an increased risk of developing bacterial/fungal superinfections is frequently seen in patients with symptomatic HCMV disease but not in asymptomatic CMV antigenemia. The risk of developing superinfections can be predicted by flow-cytometric monitoring of peripheral blood monocytes.

A high prevalence of cytomegalovirus antigenaemia in patients with moderate to severe chronic plaque psoriasis: an association with systemic tumour necrosis factor alpha overexpression

Microbiological aspects are considered to be of pathophysiological importance in psoriasis, but there has so far been no information regarding cytomegalovirus (CMV) infection. This is of interest due to the high prevalence of latent infection in the general population, the frequent reactivation in inflammatory diseases, and the immunomodulating capacity of CMV. To detect active infection we analysed CMV antigen expression of peripheral blood mononuclear cells (PBMC) from psoriatic patients (n = 30) in comparison with healthy volunteers (n = 65). Using three monoclonal antibodies and immunocytological staining (alkaline phosphatase-antialkaline phosphatase technique), we frequently found CMV antigenaemia in psoriasis (43%) compared with healthy laboratory staff (12%, P < 0. 01) and blood donors (6%, P < 0.001). Clearance of CMV antigenaemia was observed with antipsoriatic treatment. CMV antigenaemia was symptomless, and was associated with seropositivity for anti-CMV IgG but not IgM antibodies, indicating subclinical activation of latent infection. Serological investigations in 85 psoriatic patients gave no evidence for a higher prevalence of latent CMV infection. In psoriatic lesions, CMV DNA was only rarely detected by polymerase chain reaction. As it has been shown that tumour necrosis factor (TNF)-alpha can induce CMV reactivation, we determined TNF-alpha plasma concentrations and mRNA expression in PBMC from psoriatic patients. Elevated TNF-alpha levels were found and correlated with the frequency of CMV antigen-expressing PBMC, suggesting a critical role of TNF-alpha in CMV activation. We speculate that active, subclinical CMV infection may be of pathophysiological importance in psoriasis.

Human cytomegalovirus infection of human hematopoietic progenitor cells

For a number of years it has been well established that human cytomegalovirus (HCMV) can be transmitted by the cellular components of blood. HCMV is also associated with a number of hematologic disorders. Although HCMV was thought to be present in blood cells in a latent or persistent form, it was not known how the virus was maintained and which cells were the carriers of HCMV. In addition to peripheral blood cells, there has been clinical evidence that HCMV may be associated with specific disorders of the hematopoietic system. Recently, a number of advances in cell and molecular biology have helped to develop a better understanding of the relationship between HCMV and the hematopoietic system. The application of the polymerase chain reaction (PCR) to the study of HCMV infection has revealed that the virus was present in mononuclear cells with only limited transcription of its genome. Studies conducted in our laboratory have demonstrated that both CD34+ progenitor cells and monocytes could be infected with HCMV and virus recovered when the cells were allowed to terminally differentiate. Subsequently, these results have been confirmed in vivo: HCMV DNA and limited RNA transcripts could be detected in in vivo infected hematopoietic progenitor cells and HCMV has been rescued from macrophages derived through in vitro differentiation of monocytes from normal seropositive blood donors. Although our understanding of the relationship between HCMV and the hematopoietic system has been advanced, the mechanisms by which the virus can be maintained in a latent state and how it is reactivated is still unclear. Furthermore, it remains to be determined what HCMV-mediated effect is responsible for the inhibition of hematopoiesis following an in vitro infection and its significance in vivo.

Improvement in the outcome of rejection with pentoxifylline in renal transplantation: a randomized controlled trial

BACKGROUND

Pentoxifylline (PTX), a methylxantine phosphodiesterase inhibitor commonly used to treat peripheral vascular disease, has been shown to decrease the production of proinflammatory cytokines and reactive oxygen species and to reduce the toxic effects of cyclosporine. Thus, administration of PTX to transplant patients, as an adjunct to immunosuppressive therapy, could prevent numerous posttransplantation complications.

METHODS

One hundred forty consecutive patients receiving cadaveric kidney grafts were registered in a randomized double-blind study comparing PTX at a dose of 800 mg/day, then 1200 mg/day, versus placebo during the first 6 months after transplantation. All patients were followed up for 1 year.

RESULTS

Rejection episodes were validated as the only independent risk factor for graft loss in this study. We compared graft survival rates in each group according to the presence or absence of acute rejection. Acute rejection reduced graft survival in the control group (graft survival rate at 1 year, 59% vs. 97%, P < 0.001), but this adverse effect was blunted in the PTX group (72% vs. 89%, NS). This improvement was confirmed by multivariate analysis for risk factors, with graft survival rates being described at best as the interaction between rejection and treatment (PTX vs. placebo, P = 0.045).

CONCLUSION

Although PTX does not modify the incidence of any posttransplant complications, it weakens the consequences of rejection on graft survival.