Herpesvirus Saimiri encodes a new cytokine, IL-17, which binds to a novel cytokine receptor

Enhancing Effect of IL-17 on IL-1-Induced IL-6 and Leukemia Inhibitory Factor Production by Rheumatoid Arthritis Synoviocytes and Its Regulation by Th2 Cytokines

IL-17 is a cytokine produced by CD4 T cells that activates the production of inflammatory mediators by synoviocytes. To study the contribution of soluble factors in the interaction between T cells and synoviocytes in rheumatoid arthritis (RA), we looked at the effect of IL-17 on these cells in the presence of cytokines classified as pro (IL-1)- and anti-inflammatory (IL-4, IL-13, IL-10). Both human rIL-1β and rIL-17 induced IL-6 and leukemia inhibitory factor (LIF) production by synovial fibroblasts in a dose-dependent manner. After 7 days of culture, optimal concentrations of IL-1β increased IL-6 (33-fold) and LIF (10-fold) production by synoviocytes, while IL-17 showed a lesser effect on IL-6 (17-fold) and LIF (4-fold) production. Using low concentrations of IL-17 and IL-1β in combination, a synergistic effect was observed on the production of IL-6, whereas an additive effect was observed for LIF production. Production of biologically active IL-17 was demonstrated in RA synovium supernatants with the use of a blocking anti-IL-17 Ab. Both IL-4 and IL-13 had a modest stimulatory effect on IL-1- and IL-17-induced production of IL-6, but inhibited that of LIF. In contrast, IL-10 had a limited inhibitory effect on IL-6 production and no effect on that of LIF. These findings indicate that low levels of cytokines produced by monocytes (IL-1) and T cells (IL-17) can act together on synoviocytes. Thus, some RA synovium T cells producing IL-17 can activate mesenchymal cells leading to an increased proinflammatory pattern sensitive to Th2 cytokine regulation.

A functional fibroblast growth factor-1 immunoglobulin fusion protein

Proteins of the fibroblast growth factor (FGF) family play diverse roles in embryonic development, angiogenesis, and wound healing. The most well studied targets of FGF activity typically are cells of mesodermal and neuroectodermal origin; in addition, expression of FGF-1 (acidic FGF) is increased at several sites of chronic immunologic injury, and recent studies show that FGF-1 also may interact with cells of the immune system. In some human T cells, FGF-1 can induce signals necessary for production of interleukin-2, a key cytokine required for T cell proliferation. To better characterize the interaction of FGF-1 with FGF receptors on T cells, a fusion protein was constructed containing a portion of the constant region of human IgG1 (Fc) at the amino terminus of FGF-1. The Fc-FGF-1 fusion protein retained FGF function as determined by stimulation of tyrosine phosphorylation and DNA synthesis in NIH 3T3 cells. Binding of the intact fusion protein to FGF receptor 1 (FGFR1) on T cells was demonstrated by immunoprecipitation of the receptor bound to Fc-FGF-1 and by flow cytometry showing binding of fusion protein to T cells expressing FGFR1. This functional Fc-FGF-1 protein should prove useful in identifying FGFR-expressing cells.

Pathogen interactions with cytokines and host defence: an overview

This review summarises some of the immune evasion tactics adopted by pathogens. They include the antagonism of immune function through the use of homologues of cytokine receptors, expression of viral proteins which interact with cytokine signal transduction and expression of cytokine mimics and host proteins that influence the Type I or II cytokine responses. Some of the viral defense molecules that interfere with the functions of cytokines include the EBV protein BCRF1 (viral IL-10) which blocks synthesis of cytokines such as IFN-gamma, viral IL-17 and IL-8 receptor encoded by the herpesvirus saimiri genome and chemokine receptor homologues of Epstein-Barr virus, herpesvirus saimiri and cytomegalovirus. These immunomodulatory tactics function to protect the host from the lethal inflammatory effects as well as inhibit the local inflammatory response elicited to kill the foreign pathogen. Other strategies include the alterations in cytokine expression such as demonstrated with the hepatitis B virus (HBV) core protein and terminal protein which can inhibit interferon-beta gene expression, the interactions of the hepatitis C virus core protein to lymphotoxin-beta receptor and the effects of the interferon signal transduction pathway by adenovirus EIA oncogene and HBV by reducing levels or activity of the cytosolic latent transcriptional factors (STATS). Immune evasive strategies of helminth parasites related to cytokine activities will also be briefly discussed.

Regulation of granulocyte colony-stimulating factor gene expression by interleukin-17

Interleukin-17 (IL-17) has been previously reported to induce stromal cells to produce a number of hematopoietic and proinflammatory cytokines, including granulocyte colony-stimulating factor (G-CSF). Here, we have evaluated the mechanisms responsible for the augmentation of G-CSF gene expression by IL-17, using the murine 3T3 fibroblast cell line. Treatment of 3T3 cells, but not primary bone marrow-derived macrophages or murine monocyte/macrophage cell lines, resulted in increased steady-state G-CSF mRNA levels within 2-4 h and augmented G-CSF protein production. The combination of IL-17 and LPS enhanced G-CSF expression in an additive fashion. Stability studies revealed that IL-17 stabilized G-CSF mRNA levels, with a t1/2 of 4 h, compared to a t1/2 of less than 2 h in medium or LPS-treated cells. Induction of G-CSF expression in 3T3 cells by IL-17 did not appear to require tyrosine kinase activation or de novo protein synthesis. These studies indicate that post-transcriptional mechanisms play an important role in IL-17-induced G-CSF expression in fibroblasts and suggest that IL-17 may be useful for further delineating mechanisms of G-CSF gene regulation.

Gammadelta+ T cells preferentially respond to live rather than killed malaria parasites

We have compared the in vitro responses of peripheral blood T cells from malaria-unexposed donors to live Plasmodium falciparum schizonts, freeze-thawed schizont extracts (P. falciparum schizont extracts [PfSE]), and parasite culture supernatants. We show that the cells responding to PfSE and parasite culture supernatants are predominantly CD4+ TCR alphabeta+ while in the presence of live schizonts there is an additional activation of TCR gammadelta+ cells. Activation of TCR gammadelta+ cells in response to PfSE was seen only when irradiated autologous feeder cells or recombinant interleukin-2 (IL-2) was added to the cultures. Live schizonts but not PfSE induced significant IL-2 production in vitro in the first 5 days after stimulation, suggesting that induction of early IL-2 by live parasites may contribute to the marked activation of the TCR gammadelta+ population.

A poxvirus-encoded semaphorin induces cytokine production from monocytes and binds to a novel cellular semaphorin receptor, VESPR

The vaccinia virus A39R protein is a member of the semaphorin family. A39R.Fc protein was used to affinity purify an A39R receptor from a human B cell line. Tandem mass spectrometry of receptor peptides yielded partial amino acid sequences that allowed the identification of corresponding cDNA clones. Sequence analysis of this receptor indicated that it is a novel member of the plexin family and identified a semaphorin-like domain within this family, thus suggesting an evolutionary relationship between receptor and ligand. A39R up-regulated ICAM-1 on, and induced cytokine production from, human monocytes. These data, then, describe a receptor for an immunologically active semaphorin and suggest that it may serve as a prototype for other plexin-semaphorin binding pairs.

IL-17 Stimulates the Production and Expression of Proinflammatory Cytokines, IL-β and TNF-α, by Human Macrophages

IL-17 is a newly described, T cell-derived cytokine with ill-defined physiologic properties. As such, we examined the release of proinflammatory mediators by human macrophages in response to recombinant human (rh) IL-17. IL-1β and TNF-α expression and synthesis were up-regulated by rhIL-17 in a dose (ED50 was 50 ± 9 ng/ml)- and time-dependent fashion, with cytokine accumulation reaching a zenith after 9 h. Release of IL-6, PGE2, IL-10, IL-12, IL-1R antagonist, and stromelysin was also stimulated by rhIL-17. IL-1β and TNF-α mRNA expression levels were controlled by rhIL-17 in a complex manner with an initial 30-min inhibitory phase, and then up-regulation beginning at 1 h and reaching a plateau at about 3 h. The latter expression pattern closely mirrored the nuclear accumulation of the transcription factor nuclear factor-κB. cAMP mimetics isobutyl-1-methylxanthine (IBMX), forskolin, PGE2, and cholera toxin reversed rhIL-17-induced release of TNF-α, but had no consistent effect on induced IL-1β synthesis. Induced release of TNF-α was also inhibited by serine/threonine protein kinase inhibitors KT-5720 (protein kinase A) and Calphostin C (protein kinase C), mitogen-activated protein kinase kinase inhibitor PD098059, and a nonspecific tyrosine kinase inhibitor, genistein. Calphostin C alone abrogated the rhIL-17-induced release of IL-1β. The antiinflammatory cytokines IL-4 (p < 0.01) and IL-10 (p < 0.02) completely reversed rhIL-17-stimulated IL-1β release, while IL-13 and TGF-β2 were partially effective (59 and 43% diminution, respectively). IL-10 exerted a significant suppressive effect on IL-17-induced TNF-α release (99%, p < 0.02), while the inhibitory effects of IL-4, IL-13, and TGF-β2 on TNF-α secretion were partial (48, 10, and 23%, respectively). The data suggest a pivotal role for IL-17 in initiating and/or sustaining an inflammatory response.

The novel receptor TRAIL-R4 induces NF-kappaB and protects against TRAIL-mediated apoptosis, yet retains an incomplete death domain

A fourth member of the emerging TRAIL receptor family, TRAIL-R4, has been cloned and characterized. TRAIL-R4 encodes a 386-amino acid protein with an extracellular domain showing 58%-70% identity to those of TRAIL-R1, TRAIL-R2, and TRAIL-R3. The signaling capacity of TRAIL-R4 is similar to that of TRAIL-R1 and TRAIL-R2 with respect to NF-kappaB activation, but differs in its inability to induce apoptosis. Yet TRAIL-R4 retains a C-terminal element containing one third of a consensus death domain motif. Transient overexpression of TRAIL-R4 in cells normally sensitive to TRAIL-mediated killing confers complete protection, suggesting that one function of TRAIL-R4 may be inhibition of TRAIL cytotoxicity. Like TRAIL-R1 and TRAIL-R2, this receptor shows widespread tissue expression. The human TRAIL-R4 gene has been mapped to chromosome 8p22-21, clustered with three other TRAIL receptors.

The superantigen-homologous viral immediate-early gene ie14/vsag in herpesvirus saimiri-transformed human T cells

Herpesvirus saimiri C488 transforms human T lymphocytes to stable growth in culture. The growth-transformed human T cells harbor the viral genome in a nonintegrated episomal form without production of virus particles. In these cells, virus gene expression was previously found to be confined to the transforming genes stpC and tip. In order to analyze virus gene expression in more detail, we applied a subtractive hybridization technique and compared stimulated virus-transformed cells with uninfected parental T cells of the same donor. A number of known T-cell activation genes were isolated. Viral stpC/tip cDNAs were enriched after subtraction. In addition, the viral immediate-early, superantigen-homologous gene ie14/vsag was represented by numerous cDNA clones that comprised the entire spliced transcript. Whereas a weak basal expression of ie14/vsag was detected by reverse transcription-PCR only, the phorbol ester-induced transcripts were readily shown by Northern blotting. ie14/vsag, which before had been classified as a major immediate-early gene of herpesvirus saimiri, is localized within a highly conserved region with extensive homologies to the cellular genome. Mutant viruses without the ie14/vsag gene are replication competent and fully capable of transforming human and marmoset T cells. Since ie14/vsag is transiently expressed after stimulation, it may increase T-cell proliferation in an activation-dependent and superantigen-like but apparently Vbeta-independent way.

A homologue of the TNF receptor and its ligand enhance T-cell growth and dendritic-cell function

Dendritic cells are rare haematopoietic cells that reside in a number of organs and tissues. By capturing, processing and presenting antigens to T cells, dendritic cells are essential for immune surveillance and the regulation of specific immunity. Several members of the tumour necrosis factor receptor (TNFR) superfamily are integral to the regulation of the immune response. These structurally related proteins modulate cellular functions ranging from proliferation and differentiation to inflammation and cell survival or deaths. The functional activity of dendritic cells is greatly increased by signalling through the TNFR family member CD40. Here we report the characterization of RANK (for receptor activator of NF-kappaB), a new member of the TNFR family derived from dendritic cells, and the isolation of a RANK ligand (RANKL) by direct expression screening. RANKL augments the ability of dendritic cells to stimulate naive T-cell proliferation in a mixed lymphocyte reaction, and increases the survival of RANK+ T cells generated with interleukin-4 and transforming growth factor (TGF)-beta. Thus RANK and RANKL seem to be important regulators of interactions between T cells and dendritic cells.

A primer on cytokines: sources, receptors, effects, and inducers

Protection against pathogens is a prerequisite for survival of most organisms. To cope with this continuous challenge, complex defense mechanisms have evolved. The construction, adaptation, and maintenance of these mechanisms are under control of an extensive network of regulatory proteins called cytokines. A great number of cytokines have been described over the last 2 decades. This review consists of an overview of cytokines that are involved in immune responses and describes some historical and general aspects as well as prospective clinical applications. Major biological effects together with information on cytokine receptors, producers, inducers, and biochemical and molecular characteristics are listed in tables. In addition, some basic information is given on cytokine receptor signal transduction. Finally, the recent discoveries of cytokine receptors functioning as coreceptors in the pathogenesis of human immunodeficiency virus are summarized.

Enhanced downregulation of Lck-mediated signal transduction by a Y114 mutation of herpesvirus Saimiri tip

Tip of herpesvirus saimiri associates with Lck and downregulates Lck function in cellular signal transduction. In this report, we demonstrate that mutation of tyrosine 114 of Tip significantly increases Lck-binding activity. This mutant exhibits a dramatic increase in the suppression of cellular tyrosine phosphorylation and surface expression of lymphocyte antigens in comparison with wild-type Tip. In addition, the expression of TipY114 converted the transforming morphology of fibroblasts induced by oncogenic F505 Lck to a normal cellular morphology. These results further support a mechanism by which the association of Tip with Lck negatively regulates Lck-mediated signal transduction.

Role of the extracellular domain of human herpesvirus 7 glycoprotein B in virus binding to cell surface heparan sulfate proteoglycans

In an attempt to identify the human herpesvirus 7 (HHV-7) envelope protein(s) involved in cell surface binding, the extracellular domain of the HHV-7 glycoprotein B (gB) homolog protein was cloned and expressed as a fusion product with the Fc domain of human immunoglobulin G heavy chain gamma1 (gB-Fc) in an eukaryotic cell system. Indirect immunofluorescence followed by flow cytometric analysis revealed specific binding of gB-Fc to the membrane of SupT1 cells but not to other CD4+ T-lymphoblastoid cell lines, such as Jurkat or PM1, clearly indicating that gB-Fc did not bind to the CD4 molecule. This was also suggested by the ability of gB-Fc to bind to CD4-negative fibroblastoid Chinese hamster ovary (CHO) cells. The binding was abrogated by enzymatic removal of cell surface heparan sulfate proteoglycans by heparinase and heparitinase but not by treatment with condroitinase ABC. In addition, binding of the gB-Fc fusion protein to CHO cells was severely impaired in the presence of soluble heparin, as well as when heparan sulfate-deficient mutant CHO cells were used. Consistent with these findings, soluble heparin was found to block HHV-7 infection and syncytium formation in the SupT1 cell line. Although the CD4 antigen is a critical component of the receptor for the T-lymphotropic HHV-7, these findings suggest that heparin-like molecules also play an important role in HHV-7-cell surface interactions required for infection and that gB represents one of the HHV-7 envelope proteins involved in the adsorption of virus-to-cell surface proteoglycans.

Pathological changes in the spleens of gamma interferon receptor-deficient mice infected with murine gammaherpesvirus: a role for CD8 T cells

Murine gammaherpesvirus is a natural rodent pathogen which causes a primary infection in the lungs and establishes a persistent infection in B lymphocytes. During the primary infection, large amounts of gamma interferon (IFN-gamma) are produced by spleen, mediastinal, and cervical lymph node cells. To investigate the role of IFN-gamma in control of the virus infection, mice lacking the cellular receptor for IFN-gamma (IFN-gamma R-/- mice) were infected with murine gammaherpesvirus 68 (MHV68). IFN-gamma R-/- mice showed no difference from wild-type mice in the titers of infectious virus in the lungs or in the rate of clearance of the lung infection. In the spleen, however, clear differences were observed. By 14 days postinfection, spleens from IFN-gamma R-/- mice were pale, shrunken, and fibrous. Histological examination showed that there was an early (day 10) infiltration of granulocytes followed by widespread destruction of splenic architecture (days 14 to 17). A marked decrease in the number of splenic B cells and CD4+ and CD8+ T cells occurred. These changes were accompanied by a 10- to 100-fold greater load of latently infected cells in IFN-gamma R-/- mice than in wild-type mice at 14 to 17 days postinfection, but this was reduced to the levels found in wild-type mice by 21 days postinfection. Treatment of the mice with the antiviral drug 2'-deoxyl-5-ethyl-beta-4'-thiouridine from 6 days postinfection did not prevent the occurrence of these changes. The changes were, however, completely reversed by depletion of CD8+ T cells prior to and during the primary infection. Depletion of CD4+ T cells also reversed the major pathological and virological changes, although in this case there was evidence of some histological changes. Thus, the lack of IFN-gamma receptor had profound consequences in spleens of MHV68-infected mice. The possible mechanisms involved in these changes are discussed.

Epstein-Barr virus uses HLA class II as a cofactor for infection of B lymphocytes

Infection of B lymphocytes by Epstein-Barr virus (EBV) requires attachment of virus via binding of viral glycoprotein gp350 to CD21 on the cell surface. Penetration of the cell membrane additionally involves a complex of three glycoproteins, gH, gL, and gp42. Glycoprotein gp42 binds to HLA-DR. Interference with this interaction with a soluble form of gp42, with a monoclonal antibody (MAb) to gp42, or with a MAb to HLA-DR inhibited virus infection. It was not possible to superinfect cells that failed to express HLA-DR unless expression was restored by transfection or creation of hybrid cell lines with complementing deficiencies in expression of HLA class II. HLA class II molecules thus serve as cofactors for infection of human B cells.

Interleukin-17 up-regulation of nitric oxide production in human osteoarthritis cartilage

OBJECTIVE

To examine the effect of human interleukin-17 (IL-17) on nitric oxide (NO) production in human osteoarthritis (OA) cartilage under ex vivo conditions.

METHODS

OA cartilage from patients undergoing knee replacement surgery was used in explant assays to assess the effect of IL-17. NO production was measured by estimating the stable NO metabolite, nitrite, in conditioned medium.

RESULTS

IL-17 augmented the spontaneous production of nitric oxide. This augmentation was sensitive to cycloheximide and pyrrolidine dithiocarbamate, but not to dexamethasone or soluble IL-1 receptor.

CONCLUSION

IL-17 augments nitric oxide production in OA cartilage via nuclear factor kappaB activation, but independently of IL-1beta signaling.

Tap: a novel cellular protein that interacts with tip of herpesvirus saimiri and induces lymphocyte aggregation

Tip of herpesvirus saimiri associates with Lck and down-regulates Lck-mediated activation. We identified a novel cellular Tip-associated protein (Tap) by a yeast two-hybrid screen. Tap associated with Tip following transient expression in COS-1 cells and stable expression in human Jurkat-T cells. Expression of Tip and Tap in Jurkat-T cells induced dramatic cell aggregation. Aggregation was likely caused by the up-regulated surface expression of adhesion molecules including integrin alpha, L-selectin, ICAM-3, and H-CAM. Furthermore, NF-kappaB transcriptional factor of aggregated cells had approximately 40-fold higher activity than that of parental cells. Thus, Tap is likely to be an important cellular mediator of Tip function in T cell transformation by herpesvirus saimiri.

Masters of deception: a review of herpesvirus immune evasion strategies

Herpesviruses have acquired a variety of different mechanisms to avoid the damaging effects of host immunity. Frequently, these viruses subvert normal immune regulatory functions utilized by the host. The focus of this review is upon herpesvirus genes encoding known or potential immunomodulatory proteins. Areas covered include inhibition of complement and antibody function, herpesvirus-encoded homologues of cytokines and chemokine receptors, and potential disruption of cellular recognition of virally infected targets.

Use of virion DNA as a cloning vector for the construction of mutant and recombinant herpesviruses

We have developed improved procedures for the isolation of deletion mutant, point mutant, and recombinant herpesvirus saimiri. These procedures take advantage of the absence of NotI and AscI restriction enzyme sites within the viral genome and use reporter genes for the identification of recombinant viruses. Genes for secreted engineered alkaline phosphatase and green fluorescent protein were placed under simian virus 40 early promoter control and flanked by NotI and AscI restriction sites. When permissive cells were cotransfected with herpesvirus saimiri virion DNA and one of the engineered reporter genes cloned within herpesvirus saimiri sequences, recombinant viruses were readily identified and purified on the basis of expression of the reporter gene. Digestion of recombinant virion DNA with NotI or AscI was used to delete the reporter gene from the recombinant herpesvirus saimiri. Replacement of the reporter gene can be achieved by NotI or AscI digestion of virion DNA and ligation with a terminally matched fragment or, alternatively, by homologous recombination in cotransfected cells. Any gene can, in theory, be cloned directly into the virion DNA when flanked by the appropriate NotI or AscI sites. These procedures should be widely applicable in their general form to most or all herpesviruses that replicate permissively in cultured cells.

Regulation of the herpesvirus saimiri oncogene stpC, similar to that of T-cell activation genes, in growth-transformed human T lymphocytes

Herpesvirus saimiri strain C488, a T-cell tumor virus of New World primates, transforms human T lymphocytes to stable interleukin-2-dependent growth without need for further stimulation by antigen or mitogen. The transformed cell lines show the phenotype of activated mature T cells and retain many essential features of the primary parental cells, e.g., antigen specificity. In contrast to transformed New World monkey T cells, the human lines do not support lytic growth of the virus, even after chemical stimulation. Here we show that many viral genes remain silent during episomal persistence. However, the viral oncogene stpC is predominantly transcribed and translated to a stable cytoplasmic protein of 20 kDa that is heterogeneously expressed in individual cells. This 1.7-kb mRNA is bicistronic, encoding also Tip, a viral protein interacting with the T-cell-specific tyrosine kinase Lck. stpC/tip transcripts are heavily induced upon stimulation by mitogen or phorbol ester. Block of protein synthesis does not abolish transcription: treatment with cycloheximide greatly induces stpC/tip mRNA levels. Thus, this gene complex is regulated similarly to early T-cell activation genes. Constitutive and induced expression engage different transcription start sites. The T-cell regulation of the viral genes stpC and tip may contribute to the T-cell tropism of growth transformation by herpesvirus saimiri.

Mouse IL-17: a cytokine preferentially expressed by alpha beta TCR + CD4-CD8-T cells

A novel cytokine originally designated murine CTLA-8 was described as a cDNA isolated from an activated T cell hybridoma produced by fusing a mouse cytotoxic T cell clone and a rat T lymphoma. This cDNA, which contains mRNA instability sequences characteristic of many cytokines, encoded a putative secreted protein that was homologous to the ORF13 gene of Herpesvirus saimiri. The human homolog to this molecule has recently been identified as the proinflammatory cytokine IL-17. We describe the isolation of a cDNA encoding mouse IL-17 from a cDNA library generated from alpha beta TCR + CD4-CD8- thymocytes using a subtraction technique that enriched for activation specific genes. This cDNA shares 87.3% amino acid identity to the previously described murine CTLA-8. Comparison of murine CTLA-8 to a cDNA we isolated from activated rat splenocytes revealed that murine CTLA-8 is, in fact, the rat homolog of IL-17. Mouse IL-17 mRNA is specifically expressed by activated alpha beta TCR + CD4-CD8- T cells, a small subset with a potentially important role in immune regulation. Mouse, rat, and human IL-17 can induce IL-6 secretion in mouse stromal cells, indicating that all homologs can recognize the mouse receptor.

One step ahead of the game: viral immunomodulatory molecules

For decades cell biologists have relied on viruses to facilitate the study of complex cellular function. More recently, the tragedy of the AIDS epidemic has focused considerable human and financial resources on both virology and immunology, resulting in the generation of new information relating these disciplines. As the miracle of the mammalian immune system unfolds in the laboratory, the elegance of the mechanisms used by co-evolving viruses to circumvent detection and destruction by the host becomes inescapably obvious. Although many observation of virus-induced phenomena that likely contribute to the virus's escape of immune surveillance are still empirical, many other such phenomena have now been defined at the molecular level and confirmed in in vivo models. Immune modulators encoded within viral genomes include proteins that regulate antigen presentation, function as cytokines or cytokine antagonists, inhibit apoptosis, and interrupt the complement cascade. The identification of such gene products and the elucidation of their function have substantially strengthened our understanding of specific virus-host interactions and, unexpectedly, have contributed to the recognition of potent synergy between viruses, which can result in an unpredictable exacerbation of disease in co-infected individuals. Because many viral immune modulators clearly have host counterparts, viruses provide a valuable method for studying normal immune mechanisms. It is conceivable that an improved understanding of virus-encoded immunomodulators will enhance our ability to design reagents for use in therapeutic intervention in disease and in vaccine development.

Complete nucleotide sequence of the mouse CTLA8 gene

The gene encoding the mouse cytotoxic T-lymphocyte-associated antigen 8 (CTLA8) has been cloned and its complete nucleotide (nt) sequence determined. Sequence and polymerase chain reaction (PCR) analysis indicated that the published CTLA8 sequence[Rouvier et al., J. Immunol. 150 (1993), 5445-5456] was of rat rather than mouse origin. The mouse CTLA8 gene contains two exons and one intron. The 5'flanking region contains several consensus motifs for binding to transcription factors and the 3' untranslated region (UTR) has AU-rich motifs associated with RNA instability. The putative exon sequences predict that the full-length mouse CTLA8 molecule contains 147 amino acids (aa) and shares 88% aa identity with rat CTLA8 and 57% aa identity to HSV13, an open reading frame (ORF) from herpesvirus saimiri (HVS).