Increased tumorigenicity of cells carrying recombinant human herpesvirus 8.

Human herpesvirus 8 (HHV-8) infection is associated with the development of Kaposi's sarcoma and primary effusion lymphoma. The cloning of the HHV-8 genome into a bacterial artificial chromosome (BAC) allows researchers to mutate and identify the relative importance of HHV-8 genes essential for growth and replication in tissue culture systems. However, in vivo models to study the impact of such mutations are very limited. Consequently, the objective of this study was to determine whether cells carrying the HHV-8 BAC would form tumors when injected into mice, enabling the use of this model to assess the influence of viral gene mutation on tumorigenesis. To do so, 293T and 293T-E1 cells carrying recombinant HHV-8 were injected into SCID mice and tumor growth was analyzed. Our results clearly show that mice injected with 293T-E1 cells had a significantly higher tumor incidence level as well as increased tumor volumes and weights compared to mice injected with 293T control cells. Cells carrying the HHV-8 genome grew faster and more aggressively in SCID mice than control 293T cells, highlighting the oncogenic properties of HHV-8. The model presented could therefore be used for the identification of HHV-8 genes contributing to tumorigenesis in the context of the entire viral genome.

[Early phase of HHV6 infection: role of IE1 and IE2 proteins]. / La phase très précoce de l'infection par le sixième herpèsvirus humain: rôle des protéines IE1 et IE2.

Human herpesvirus 6 (HHV6) is an opportunistic pathogen whose infection or reactivation is associated with diseases such as roseola, central nervous system disorders and organ transplant anomalies. Following its entry into the host cell, the virus utilizes the cellular machinery in order to transcribe its genes and insure the replicative cycle progression. HHV-6 can also latently persist in its host. Immediate-early proteins are rapidly expressed upon cell infection. In particular, IE1 and IE2 proteins play an important role in the establishment of infection. IE1 inhibits interferon-b transcription and may participate in the PML nuclear body aggregation induced by the viral infection. IE2 is a strong transactivator of multiple cell and viral promoters, and contributes to the initiation of the replicative cycle. In this review we have synthesized the current body of knowledge pertaining to the immediate early phase of HHV6 infection, including the role of immediate-early proteins in the replicative cycle and during latency, as well as that of the promoter who regulates their expression.

Phenotypic alterations and survival of monocytes following infection by human herpesvirus-6.

Freshly isolated monocytes rapidly undergo physiological changes in vitro, resulting in programmed cell death (apoptosis). Activation of monocytes, which promotes differentiation into macrophages, is known to inhibit apoptotic processes. In the present study, we report that human herpesvirus-6 (HHV-6) prevents monocytes from undergoing spontaneous apoptosis during the first 72 hours of culture. Furthermore, significant alterations in cell-surface phenotype were observed after 72 hours of infection with HHV-6. HHV-6-infected monocyte cultures have considerably reduced levels of CD14, CD64 (FcgammaRI) and HLA-DR antigen on their surface, while CD32 (FcgammaRII) expression is unaffected. On the basis of these results, we hypothesize that HHV-6 promotes monocytes survival and causes phenotypic modifications that could favor immune evasion and ensure its persistence within the infected host.

Epstein-Barr virus primes human polymorphonuclear leucocytes for the biosynthesis of leukotriene B4.

In the present study, we have investigated the effect of the short-term incubation of polymorphonuclear leucocytes (PMN) with infectious Epstein-Barr virus (EBV) on leukotriene B(4) (LTB(4)) biosynthesis. Pre-exposure of PMN to EBV led to an increased production of LTB(4) upon stimulation with either the ionophore A23187, the chemotactic peptide fMLP, or phagocytic particles (zymosan). Experiments performed with viral particles pretreated with a neutralizing antibody raised against the gp350 of the viral envelope revealed that a specific interaction between the PMN surface and the viral glycoprotein gp350 is required for the priming effect of EBV. Preincubation of PMN with EBV resulted in an increased release of arachidonic acid upon stimulation with a second agonist. Moreover, LTB(4) biosynthesis in EBV/A23187-treated PMN was greatly diminished in the presence of an inhibitor of the cytosolic phospholipase A2 (cPLA(2)), suggesting that cPLA(2) plays a critical role in the priming effect of EBV. Accordingly, EBV by itself promoted Ser-505 phosphorylation of cPLA(2) and strongly enhanced fMLP-induced phosphorylation of p38 MAP kinase, an enzyme known to phosphorylate cPLA(2) in human PMN. Furthermore, fMLP-induced translocation of cPLA(2) was strongly enhanced when PMN were previously exposed to EBV. These data indicate that binding of EBV to human PMN results in the activation of intracellular events involved in the release of pro-inflammatory lipid mediators.

Human herpesvirus 8 viral FLICE-inhibitory protein inhibits Fas-mediated apoptosis through binding and prevention of procaspase-8 maturation.

Viral FLICE-inhibitory proteins (v-FLIPs) encoded by several herpesviruses and poxviruses share the ability to inhibit apoptosis after engagement of death receptors. In the current article, we provide insights into the mechanisms by which the v-FLIP of human herpesvirus 8 (HHV-8) (also referred to as Kaposi's sarcoma-associated virus) protects cells from apoptosis after Fas-induced signaling. Using v-FLIP expression vectors, our results clearly show that HHV-8 v-FLIP reduces the cleavage of procaspase-8 into its active p18 and p10 protease subunits upon Fas-induced cell death. These results were confirmed by lower caspase-8 and caspase-3 protease activities in extracts of HeLa cells expressing HHV-8 v-FLIP. Coimmunoprecipitation studies further indicate that HHV-8 v-FLIP physically interacts with procaspase-8, but not with Fas-associated protein with death domain in the cellular cytoplasm. These results suggest that binding of HHV-8 v-FLIP to procaspase-8 affects the recruitment and the activation of the latter at the death-induced signaling complex, resulting in diminished apoptotic cascade initiation. Because cellular FLIP was recently reported to modulate promoter containing NF-kappaB motifs and that both HHV-8 and human immunodeficiency virus type 1 (HWV-1) can infect monocytes, we studied the effects of v-FLIP on HIV-1 gene expression. Cotransfection experiments indicated that v-FLIP expression is associated with activation of HIV long terminal repeats: events that were strictly dependent on the presence of NF-kappaB consensus elements. In conclusion, HHV-8 v-FLIP can possibly contribute to the pathogenesis of both HHV-8 and HIV-1 through impaired Fas-dependent killing of infected cells by cytotoxic T cells and through activation of HIV gene expression.

EBV suppresses prostaglandin E2 biosynthesis in human monocytes.

It is well known that EBV has developed strategies to evade immune surveillance. Previously, EBV was shown to bind specifically to monocytes and regulate expression of proinflammatory mediators such as IL-1, IL-6, TNF-alpha, and leukotrienes. EBV was also found to affect phagocytosis of monocytes. In this study, we show that in addition to these effects, EBV suppresses the biosynthesis of PGE2, a pleiotropic immunomodulatory molecule that is synthesized by the dioxygenation of arachidonic acid via the cyclooxygenase (COX) pathway. This down-regulation of PGE2 formation involved the inhibition of the inducible COX-2 isoform expression both at the transcriptional and translational levels, whereas expression of the constitutive COX-1 isoform was unaltered. Furthermore, exposure of monocytes to EBV was found to impact on the NF-kappaB activation pathway, which plays an essential role in the induction of COX-2 in monocytes. The inhibition of PGE2 biosynthesis was relieved when the experiments were conducted in presence of phosphonoacetic acid, an inhibitor of herpesviruses DNA polymerase, indicating that viral replication and/or neosynthesized viral proteins were involved in this process. Thus, inhibition of PGE2 biosynthesis in monocytes may represent an additional mechanism underlying EBV pathogenicity.

Infection of primary human monocytes by Epstein-Barr virus.

Previous studies have reported that infection of monocytes by viruses such as cytomegalovirus and human immunodeficiency virus weakens host natural immunity. In the present study, we demonstrated the capability of Epstein-Barr virus (EBV) to infect and replicate in freshly isolated human monocytes. Using electron microscopy analysis, we observed the presence of EBV virions in the cytoplasm and nuclei of approximately 20% of monocytes. This was confirmed by Southern blot analysis of EBV genomic DNA sequences in isolated nuclei from monocytes. Infection of monocytes by EBV leads to the activation of the replicative cycle. This was supported by the detection of immediate-early lytic mRNA BZLF-1 transcripts, and by the presence of two early lytic transcripts (BALF-2, which appears to function in DNA replication, and BHRF-1, also associated with the replicative cycle). The late lytic BcLF-1 transcripts, which code for the major nucleocapsid protein, were also detected, as well as EBNA-1 transcripts. However, attempts to detect EBNA-2 transcripts have yielded negative results. Viral replication was also confirmed by the release of newly synthesized infectious viral particles in supernatants of EBV-infected monocytes. EBV-infected monocytes were found to have significantly reduced phagocytic activity, as evaluated by the quantification of ingested carboxylated fluoresceinated latex beads. Taken together, our results suggest that EBV infection of monocytes and alteration of their biological functions might represent a new mechanism to disrupt the immune response and promote viral propagation during the early stages of infection.

Interleukin-15 as an activator of natural killer cell-mediated antiviral response.

Natural killer (NK) cells are large granular lymphocytes capable of efficient killing of virus-infected and tumor cells in a major histocompatibility complex-independent manner. The cytotoxic killing potential of NK cells can be modulated by a variety of factors, including cytokines such as interleukin-12 (IL-12), IL-15, and interferon (IFN). IL-15 also plays an important role in NK cell development and survival. Killing of virally infected cells by NK cells is likely to represent an important antiviral defense mechanism, especially during the early phase of infection when antigen-specific immunity has yet to be generated. In the present work, we studied the potential of IL-15 to act as a modulator of NK cell-mediated antiviral defense. Our results clearly indicate that IL-15 can curtail infections by 3 human herpesviruses: Herpes simplex virus type 1, Epstein-Barr virus, and human herpesvirus 6. The antiviral activity of IL-15 is dose-, time-, and NK cell-dependent. IL-15-treated NK cells showed an increased killing potential against a variety of cells, including virus-infected target cells. Lastly, using highly purified cell population, we report that IL-15 triggers the synthesis of IFN-gamma from both CD4(+) and NK cells, which can act in both autocrine and paracrine fashion to modulate NK cells cytotoxic potential. In conclusion, IL-15 is a cytokine that can contribute to the establishment of an antiviral state in 2 ways: first by increasing the killing ability of NK cells and second by stimulating the synthesis and secretion of IFN.

CD4 promoter transactivation by human herpesvirus 6.

The observation that human herpesvirus 6 (HHV-6) can induce CD4 gene transcription and expression in CD4(-) cells was reported several years ago (P. Lusso, A. De Maria, M. Malnati, F. Lori, S. E. DeRocco, M. Baseler, and R. C. Gallo, Nature 349:533-535, 1991) and subsequently confirmed (P. Lusso, M. S. Malnati, A. Garzino-Demo, R. W. Crowley, E. O. Long, and R. C. Gallo, Nature 362:458-462, 1993; G. Furlini, M. Vignoli, E. Ramazzotti, M. C. Re, G. Visani, and M. LaPlaca, Blood 87:4737-4745, 1996). Our objective was to identify the mechanisms underlying such phenomena. Using reporter gene constructs driven by the CD4 promoter, we report that HHV-6 can efficiently transactivate such genetic elements. Activation of the CD4 promoter occurs in the presence of the viral DNA polymerase inhibitor phosphonoformic acid, which limits expression to the immediate-early and early classes of viral genes. Using deletion mutants and specific CD4 promoter mutants, we identified an ATF/CRE binding site located at nucleotides -67 to -60 upstream of the CD4 gene transcription start site that is important for HHV-6 transactivation. The ATF/CRE site is also essential for CD4 promoter activation by forskolin, an activator of adenylate cyclase. Using electrophoretic mobility shift assays and specific antibodies, we showed that CREB-1 binds specifically to the -79 to -52 region of the CD4 promoter. Last, we have identified two open reading frames (ORFs) of HHV-6, U86 and U89 from the immediate-early locus A, that can transactivate the CD4 promoter in HeLa cells. However, transactivation of the CD4 promoter by ORFs U86 and U89 is independent of the CRE element, suggesting that additional HHV-6 ORFs are likely to contribute to CD4 gene activation. Taken together, our results will help to understand the complex interactions occurring between HHV-6 and the CD4 promoter and provide additional information regarding the class of transcription factors involved in the control of CD4 gene expression.

Epstein-Barr virus infects and induces apoptosis in human neutrophils.

The role of neutrophils during Epstein-Barr virus (EBV) infection is not known. Disruption of the initial and nonspecific immune response may favor the spread of EBV infection. We have previously shown that EBV interacts with human neutrophils and modulates protein expression. In this study we have investigated the ability of EBV to infect neutrophils. Electron microscopy studies showed penetration of virus and its subsequent localization to the nucleus. The presence of viral genomes in isolated nuclei from neutrophils was also shown by polymerase chain reaction (PCR). Expression of viral transcripts like EBNA-2 (Epstein-Barr nuclear antigen-2) and ZEBRA (BamHI Z EBV replication activator) was not detected by reverse transcriptase (RT)-PCR, suggesting that EBV does not seem to establish a latent or a lytic infection in neutrophils. However, at 20 hours post-EBV infection, 77% of cells were apoptotic as compared to 22% in uninfected cell cultures, as evaluated by flow cytometry. This EBV-induced apoptosis was prevented by the addition of granulocyte-macrophage colony-stimulating factor to the cell cultures. Apoptotic cell death seems to implicate the Fas/Fas ligand (L) pathway, as reflected by an increase of Fas/Fas L expression on neutrophils treated with EBV and an increase of soluble Fas L, which may function in an autocrine/paracrine pathway to mediate cell death. Lastly, EBV genome was detected from neutrophils of infectious mononucleosis (IM) patients in contrast to neutrophils obtained from healthy EBV-seropositive donors. Our findings on the interactions of EBV with neutrophils will then provide new insights on the immunosuppressive effects associated with EBV infection.

Activation of CD8+ T lymphocytes through the T cell receptor turns on CD4 gene expression: implications for HIV pathogenesis.

T cell activation through the T cell receptor is necessary to achieve a specific and effective immune response. We report here that stimulation of CD8+ T cells through the T cell receptor complex leads to de novo expression of the CD4 antigen on the cell surface that results in susceptibility of CD8+ T cells to HIV infection. In addition, activation of peripheral blood mononuclear cells from HIV-infected individuals results in the appearance of double-positive CD4+/CD8+ T cells, which become infected by endogenous HIV. HIV DNA sequences could be detected in uncultured and sorted mature CD3+CD8+ T cells from HIV+ individuals. These results suggest a new mechanism by which HIV could attack the immune system and may help to explain the CD8+ T cell defects in AIDS patients.

Effects of a urinary factor from women in early pregnancy on HIV-1, SIV and associated disease.

The effects of clinical grade crude preparations of human chorionic gonadotropin (hCG) on Kaposi's sarcoma, HIV, SIV and hematopoiesis were examined in vitro and in vivo. In contrast to previous studies, we report that the antiviral activity of hCG associated factors is not due to the native hCG heterodimer, including its purified subunits or its major degradation product, the beta-core. Using gel permeation chromatography of the clinical grade hCG and urine concentrates from pregnant women, we demonstrate that an as yet unidentified hCG associated factor (HAF) with anti-HIV, anti-SIV, anti-KS and pro-hematopoietic activities elutes as two peaks corresponding to 15-30 kDa and 2-4 kDa.

Association of human herpes virus 6 (HHV-6) with multiple sclerosis: increased IgM response to HHV-6 early antigen and detection of serum HHV-6 DNA.

Viruses have long been suggested to be involved in the etiology of multiple sclerosis (MS). This suggestion is based on (1) epidemiological evidence of childhood exposure to infectious agents and increase in disease exacerbations with viral infection; (2) geographic association of disease susceptibility with evidence of MS clustering; (3) evidence that migration to and from high-risk areas influences the likelihood of developing MS; (4) abnormal immune responses to a variety of viruses; and (5) analogy with animal models and other human diseases in which viruses can cause diseases with long incubation periods, a relapsing-remitting course, and demyelination. Many of these studies involve the demonstration of increased antibody titers to a particular virus, whereas some describe isolation of virus from MS material. However, no virus to date has been definitively associated with this disease. Recently, human herpesvirus 6 (HHV-6), a newly described beta-herpes virus that shares homology with cytomegalovirus (CMV), has been reported to be present in active MS plaques. In order to extend these observations, we have demonstrated increased IgM serum antibody responses to HHV-6 early antigen (p41/38) in patients with relapsing-remitting MS (RRMS), compared with patients with chronic progressive MS (CPMS), patients with other neurologic disease (OND), patients with other autoimmune disease (OID), and normal controls. Given the ubiquitous nature of this virus and the challenging precedent of correlating antiviral antibodies with disease association, these antibody studies have been supported by the detection of HHV-6 DNA from samples of MS serum as a marker of active viral infection.

Human Herpesvirus 7 induces CD4(+) T-cell death by two distinct mechanisms: necrotic lysis in productively infected cells and apoptosis in uninfected or nonproductively infected cells.

We have investigated the cytopathic effects induced by the T-lymphotropic human herpesvirus 7 (HHV-7) on the CD4(+) T-lymphoblastoid SupT1 cell line and primary CD4(+) T lymphocytes. Acute in vitro HHV-7 infection induced (1) the formation of giant multinucleated syncytia, which eventually underwent necrotic lysis, and (2) single-cell apoptosis. Both cytopathic effects increased with the progression of infection and were blocked by phosphonoformic acid, a specific inhibitor of herpetic DNA polymerase. Using electron microscopy analysis of various samples, we found that all syncytia contained large amounts of virions and that most of them exhibited clear evidence of necrosis, whereas apoptosis was predominantly observed in single cells. Although empty viral capsids could be identified in the cytoplasm of approximately 25% of single cells exhibiting an apoptotic morphology, mature virions were hardly observed in these cells. In both coculture and cell-free HHV-7 infection experiments, a significant correlation was observed between the degree of single-cell apoptosis, evaluated by quantitative flow cytometry after propidium iodide staining, and the decrease in the total number of viable cells. Moreover, in cell-free infection experiments, apoptosis showed a positive correlation also with the viral load, monitored by quantitative HHV-7 DNA polymerase chain reaction. Thus, it appears that apoptosis occurred predominantly in uninfected bystander cells but not in productively HHV-7-infected cells.

Human herpesvirus 7 induces the down-regulation of CD4 antigen in lymphoid T cells without affecting p56lck levels.

In this study, we investigated the fate of the CD4 Ag during infection of CD4+ T cells with the T lymphotrophic human herpesvirus 7 (HHV-7), using the SupT1 lymphoblastoid T cell line as a model system. The following points were established: 1) productive infection with HHV-7 was required to obtain persistent down-modulation of surface CD4 (CD4SURF); 2) at 6 to 9 days postinfection, when approximately 50 to 60% of SupT1 cells still showed a CD4SURF dim positivity, a drastic loss of total CD4 protein was found by either Western blot or immunoprecipitation experiments; 3) a block in CD4 protein production was demonstrated by a radioimmunoprecipitation assay; 4) analysis of the mRNA steady-state levels and transfection studies performed with a plasmid containing the CD4 promoter/enhancer regions in front of the luciferase gene indicated that HHV-7 infection has a suppressive effect on CD4 transcription; 5) both CD4SURF and intracellular CD4 (CD4INTRA) were reduced in HHV-7-infected cells with respect to uninfected controls, but the loss of CD4SURF was more dramatic than that of CD4INTRA; 6) immunogold labeling and electron microscopy demonstrated that CD4INTRA co-localized with HHV-7 Ags within the same subcellular compartments of infected cells; and 7) the total amount of the tyrosine kinase p56lck and tyrosine phosphorylated p56lck levels were unchanged in HHV-7-infected versus uninfected cells.

Absence of human herpesvirus 8 DNA sequences in neoplastic Kaposi's sarcoma cell lines.

The recent detection of herpesvirus-like DNA sequences in Kaposi's sarcoma (KS) lesions has led to numerous speculations regarding the role of this new agent in KS pathogenesis. However, recent studies indicate a far wider distribution of such viral sequences, shadowing the potential etiologic role of this agent in KS. In this report we show that malignant KS cell lines do not harbor such viral sequences while B cells, CD14+ and CD34+ cells do, suggesting that if a KS malignancy originates from infection with HHV-8, the virus can be lost and is not necessary for maintenance of the neoplastic state. Alternatively, HHV-8 may be a "passenger" in KS.

Cyclic AMP-responsive element-dependent activation of Epstein-Barr virus zebra promoter by human herpesvirus 6.

We have recently shown that infection of Epstein-Barr virus (EBV) genome-positive B cells by human herpesvirus 6 (HHV-6) results in the expression of the immediate-early EBV Zebra gene, followed by virus replication (L. Flamand, I. Stefanescu, D. V. Ablashi, and J. Menezes, J. Virol. 67:6768-6777, 1993). Here we show that HHV-6 upregulates Zebra gene transcription through a cyclic AMP-responsive element (CRE) located within the Zebra promoter (Zp). Using human B- or T-cell lines transfected with ZpCat reporter gene constructs, we demonstrate that a region designated the ZII domain of Zp is the target of HHV-6 transactivation. Mutation of the consensus AP-1/CRE site within ZII abolished the inducibility of Zp by HHV-6, whereas positioning of the ZII domain upstream of the beta-globin minimal promoter conferred responsiveness following HHV-6 infection. Binding of these factors to ZII was prevented by oligonucleotides containing CRE but not by AP-1 consensus sequences. Antibodies against CRE-binding (CREB) protein but not against c-Fos or c-Jun were able to supershift the DNA-protein complex, identifying the nature of the transcription factor which binds to ZII as a member of the CREB family of proteins. Finally, transfection of CREB protein and protein kinase A expression vectors were found to activate Zp in Jurkat cells, suggesting that phosphorylated form of CREB protein can play a determining role in the EBV reactivation process.

Human herpesvirus-6 enhances natural killer cell cytotoxicity via IL-15.

The marked tropism of human herpesvirus-6 (HHV-6) for natural killer (NK) cells and T lymphocytes has led us to investigate the effect of HHV-6 on cellular cytotoxicity. We describe here how HHV-6 infection of peripheral blood mononuclear cells (PBMC) leads to upregulation of their NK cell cytotoxicity. The induction of NK cell activity by HHV-6 was abrogated by monoclonal antibodies (mAbs) to IL-15 but not by mAbs to other cytokines (IFN-alpha, IFN-gamma, TNF-alpha, TNF-beta, IL-2, IL-12) suggesting that IL-15 secreted in response to viral infection was responsible for the observed effect. Furthermore, NK activation by HHV-6 was blocked with mAb to CD122, as well as by human anti-HHV-6 neutralizing antibodies. Using RT-PCR, we were able to detect IL-15 mRNA upregulation in purified monocyte and NK cell preparations. IL-15 protein synthesis was increased in response to HHV-6. Finally, addition of IL-15 to PBMC cultures was found to severely curtail HHV-6 expression. Taken together, our data suggest that enhanced NK activity in response to viral infection represent a natural anti-viral defense mechanism aimed at rapidly eliminating virus-infected cells.

Immunosuppressive effect of human herpesvirus 6 on T-cell functions: suppression of interleukin-2 synthesis and cell proliferation.

Human herpesvirus-6 (HHV-6), the etiologic agent of roseola, is ubiquitous, establishes latency in the host, and can infect a variety of immunocompetent cells, with CD4+ T lymphocytes being the targets in which it replicates most efficiently. The present study was undertaken to learn more about specific immunobiologic effects of HHV-6 infection on T-lymphocyte functions. Our data demonstrate that infection of peripheral blood mononuclear cells (PBMC) by HHV-6 results in suppression of T-lymphocyte functions, as evidenced by reduced interleukin-2 (IL-2) synthesis and cellular proliferation. In fact, HHV-6-infected PBMC secreted 50% less IL-2 than mock-infected cells after mitogenic stimulation with OKT3 antibody or phytohemmaglutinin (PHA). The inhibition of IL-2 by HHV-6 was also observed in enriched T-cell cultures, suggesting a direct effect of this virus on this cell type. Messenger RNA (mRNA) analysis by reverse-transcriptase polymerase chain reaction (PCR) indicated that HHV-6 diminishes IL-2 mRNA levels in mitogen-stimulated peripheral blood T cells. These results were also confirmed by Northern blot using the leukemic T-cell line Jurkat. This inhibitory effect of HHV-6 did not require infectious virus, as the use of UV-irradiated HHV-6 produced similar results. Moreover, HHV-6-infected PBMC showed up to an 85% reduction in their mitogen-driven proliferative response, as compared with sham-infected cells. Proliferation of both CD4+ and CD8+ T cells was affected by HHV-6. Taken together, our data show that infection of T cells by HHV-6 results in immune suppression characterized by a downregulation of IL-2 mRNA and protein synthesis accompanied by diminished cellular proliferation.